How Space Works The Facts Visually Explained - Dorling Kindersley

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• The passage discusses how astronomers visualize all celestial objects such as stars, planets, and the moon as points on an imaginary sphere surrounding Earth called the celestial sphere.

• It explains how Earth’s rotation on its axis and orbit around the sun cause the apparent motions of objects in the night sky, including the rising and setting of stars and seasonal changes in visibility.

• Key terms introduced include the celestial poles, celestial equator, and how the night sky shifts position slightly each night as Earth rotates.

• Distances provided include the average distance from Earth to the sun being about 151 million km.

So in summary, the passage explains the concept of the celestial sphere and how Earth’s motions create the illusion of movement among celestial objects as viewed from our planet.

• The passage describes various celestial objects that can be seen from Earth, either with the naked eye or with additional equipment like binoculars or telescopes.

• Objects visible to the naked eye include stars, planets like Jupiter and Venus (among the brightest objects), the Moon and its phases, constellations, and the Milky Way band.

• Binoculars allow viewing objects like the Crab Nebula, planetary rings around Saturn, and provide more detail of stars and constellations.

• A telescope opens up even more of the night sky, allowing observation of nebulae, galaxies, and meteors.

• About 9,000 stars are theoretically visible to the naked eye under perfect conditions, though only around half of those can be seen from a given location at once due to light limits.

• Additional magnification tools like binoculars and telescopes reveal greater details and more celestial objects beyond what the naked eye alone can see.

Stars twinkle because of changes in the density and temperature of Earth’s atmosphere that cause starlight to change direction slightly as it passes through the atmosphere. This effect is more noticeable for stars than planets because stars appear as point sources of light from far away. Twinkling is also more prominent for stars lower on the horizon because their light has to pass through more of the atmosphere to reach our eyes. The farther away and higher in the sky a star appears, the less it will seem to twinkle.

• The passage discusses different types of telescopes used to observe objects in space, including optical, radio, submillimeter, infrared, and ultraviolet telescopes.

• Optical telescopes, the most common, use mirrors or lenses to collect and focus visible light. Very large optical telescopes are built in high, dry places to reduce atmospheric interference. Adaptive optics can help compensate for atmospheric distortions.

• Radio telescopes are designed specifically for long-wavelength radio waves. They typically have a large parabolic dish to reflect radio signals to a subreflector and receiver. The large dish is needed to gather weak radio signals from space.

• Submillimeter, infrared, and ultraviolet telescopes observe different parts of the electromagnetic spectrum beyond what the human eye can see naturally. Looking at objects across multiple spectra provides more information.

• Examples of large optical telescopes discussed are those at the Keck Observatory in Hawaii, which use advanced technologies like segmented and adaptive primary mirrors.

The signal travels through the feed horn which increases the signal strength. Then the signal is either processed on the receiver located at the center of the dish or sent to a computer for analysis using sophisticated software. Astronomical interferometry combines light or radio signals from multiple telescopes to examine celestial objects at higher detail, as if observed by larger mirrors or antennas. The signals are processed by a digital correlator which accounts for time delays between telescopes.

• Meteoroids that enter Earth’s atmosphere are divided into two groups: pallasites and mesosiderites. Pallasites form through mixing between metallic nickel-iron cores and silicate mantles, while mesosiderites form through collisions between asteroids.

• Meteor showers occur when Earth passes through the trail of dust and particles left behind by comets as they orbit the Sun. This can result in seeing hundreds of meteors per hour radiating from a common point.

• The largest intact meteorite found on Earth is the Hoba meteorite in Namibia, weighing around 60 tons.

• Particles from space like the solar wind and cosmic rays enter Earth’s atmosphere and interact with gas molecules, sometimes causing auroras. The color of the aurora depends on the gas particles being excited at different atmospheric heights.

• Fast radio bursts are powerful but very short radio pulses from distant galaxies. Their origin is unknown. The FAST radio telescope in China can be used to listen for signals from space, like potential radio transmissions from exoplanets.

Here is a summary of the key points about the Drake equation and intelligent life in the universe:

• The Drake equation was proposed by radio astronomer Frank Drake in 1961 to estimate the number of civilizations in the universe capable of communicating.

• It calculates this number by multiplying together factors like the rate of star formation, the fraction of stars with planetary systems, the number of planets that could support life, the fraction of life-forming planets that develop intelligent life, etc.

• By accounting for all the different variables that could affect the emergence of intelligent civilizations, it provides a framework for thinking about the prevalence of life elsewhere in the universe.

• The exact values used for each factor are uncertain, so the Drake equation produces a range of potential results rather than a single number. But it shows how even small changes to probabilities can have a large impact on the estimated number of civilizations.

• Since Drake first proposed it, astronomers have refined some factors as our understanding of exoplanets, astrobiology and other fields has advanced. But it remains an important tool for considering the probability of extraterrestrial intelligent life.

Here is a summary of the key points about the internal structure, elements, and energy transfer within the Sun:

• The Sun is made up of hydrogen (75%) and helium (24%), along with smaller amounts of oxygen, carbon, nitrogen, silicon, magnesium, neon, iron, and sulfur.

• Energy is generated at the Sun’s core through nuclear fusion, which takes millions of years to travel through the radiative and convective zones to the solar surface.

• The photosphere is the visible surface layer. Above it are the chromosphere and corona, which have temperatures far higher than layers below despite being higher in the sun.

• Convection currents in the convective zone act like giant conveyor belts that circulate plasma and magnetic fields towards the surface and poles, causing sunspots to form.

• Sunspots appear in the 11-year solar cycle and can be identified using spectroscopy to analyze the sun’s spectrum and identify its chemical elements.

• During periods of high solar activity like solar maximum, more sunspots, solar flares, and coronal mass ejections occur, with consequences for space weather near Earth.

• The Moon is Earth’s natural satellite and formed from debris ejected during a giant impact between Earth and a Mars-sized planet called Theia.

• It has a solid crust made mostly of oxygen and nitrogen and is larger object visible in Earth’s night sky.

• Features include dark basalt plains called maria and light mountainous highlands. There have been 12 astronauts who have walked on the Moon.

• The Moon’s phases are caused by the changing angle of illumination by the Sun as it orbits Earth monthly. This also influences Earth’s tides.

• The Moon is slowly moving away from Earth by around 3.8 cm per year due to tidal effects. Lunar eclipses occur when the Moon passes through Earth’s shadow.

Here is a summary of the key points about Venus in the passage:

• Venus has a dense atmosphere composed mainly of carbon dioxide, which creates a powerful greenhouse effect that raises the planet’s average temperature to over 460°C.

• The greenhouse effect is exacerbated by a phenomenon known as the “runaway greenhouse effect” where volcanic activity released carbon dioxide and water vapor which warmed the planet further, causing more carbon dioxide to form in a self-perpetuating cycle.

• Venus lacks wind and weathering so its surface preserves evidence of ancient lava flows and intense volcanic activity. It has more volcanoes than any other planet, including giant pancake-shaped domes unique to Venus.

• The dense atmosphere slows volcanic eruptions compared to Earth but without wind or rain, features remain fresh-looking for a long time. Over 500 million years of active volcanism has resurfaced the planet.

• Venus has features like mountains, coronas, impact craters and many volcanoes including the largest, Maat Mons. Its surface is estimated to be less than 500 million years old.

• Venus’s atmosphere circulates in the opposite direction to its rotation via a phenomenon called “super-rotation” where atmospheric winds move faster than the planetary rotation.

• The solar day on Venus is 117 Earth days, but the equatorial atmosphere super-rotates, circulating in just 4 days due to atmospheric pressure variations caused by solar heating. The exact causes of the super-rotation are not fully understood.

• Despite Venus’s slow rotation, high-speed winds whip around the equatorial region very quickly in just four days. This super-rotation is partly due to heat from the Sun causing variations in the atmospheric pressure, but the full causes are not understood.

• Standing on the surface of Venus would feel like having 15 elephants on your shoulders due to the extreme atmospheric pressure and temperature conditions.

Here is a summary of key points about the asteroid:

• Asteroids are small rocky or metallic objects that orbit the Sun, leftover from the formation of the Solar System. They predate the planets.

• Most asteroids are found in the Main Asteroid Belt between Mars and Jupiter. Some asteroids have orbits that cross Earth’s orbit and could potentially collide with our planet.

• The largest asteroid is Ceres at 950 km across. But most are much smaller, down to a few meters. The asteroid that likely caused the extinction of the dinosaurs was over 10 km wide.

• Asteroids come in different types depending on their composition - types include carbon-rich C-type, silicate-rich S-type, and metallic M-type asteroids.

• Meteorites that reach Earth’s surface come from asteroids and provide clues about the early Solar System when analyzed.

• Space probes like Dawn have orbited and studied large asteroids Ceres and Vesta, revealing differences in their structures and compositions that hint at how they formed.

• Jupiter has the moon Io, which has intense volcanic activity due to tidal heating from Jupiter’s strong gravity. Io’s surface stretches up to 100 m every 1.5 days as it orbits Jupiter. This causes magma to churn underneath and erupt through Io’s thin crust, creating lava lakes and volcanoes up to 250 km wide.

• Another of Jupiter’s moons is Europa, which also experiences tidal heating but is further from Jupiter. This is enough to create a subsurface ocean of liquid water under Europa’s icy crust. Cracks in the ice allow liquid water to well up and sometimes erupt at the surface in the form of water plumes. The ocean may be over 100 km deep. Europa has a very smooth surface and the ice crust can move at long cracks called lineae.

Here is a summary of the key points about Europa:

• Europa has a thick icy crust atop a subsurface ocean of liquid water containing more water than all of Earth’s oceans. This subsurface ocean makes Europa a potential site to explore for signs of life.

• Beneath the ocean is believed to be a layer of rocky material and then a metallic core.

• Dark streaks called lineae on Europa’s surface are thought to be caused by movement of water underneath the icy crust.

• The thickness of Europa’s icy crust is debated, with estimates ranging from a few kilometers to over 100 km.

• Europa’s ocean is heated by tidal forces from Jupiter, keeping the ocean liquid despite being frozen on the surface.

• The subsurface ocean and potential habitability make Europa an intriguing target in the search for life elsewhere in the solar system. However, penetrating the thick icy crust to sample the ocean remains a major technological challenge.

• Saturn has a prominent ring system made up of countless chunks of almost pure water ice orbiting the planet. The rings include the bright A ring and B ring, as well as fainter outer rings like the E ring.

• The outermost ring, called the Phoebe ring, stretches all the way out to Saturn’s moon Phoebe and is very faint as it is made of extremely small particles.

• The rings are composed of around 99.9% water ice with some rocky materials from asteroids and comet impacts. Particle sizes range from dust to kilometers wide.

• Uranus and Neptune are classified as “ice giants” with mantles composed mostly of icy materials like water, ammonia and methane rather than rocky material. They have dense atmospheres dominated by hydrogen and helium.

• Both planets appear blue due to methane in their atmospheres absorbing red light. Neptune has an extra unknown chemical that makes it darker blue.

• Titan, Saturn’s largest moon, has a dense nitrogen-methane atmosphere and is the only moon known to have stable liquid on its surface, in the form of methane and ethane lakes and seas.

• Neptune is slightly smaller than Uranus, with 14 known moons and at least five rings. Storms frequently appear on its surface. Inside, it likely has an ocean of super-hot water under clouds of gas.

• Neptune has supersonic winds that swirl around the planet at speeds 1.5 times the speed of sound. Gravitation studies show these high winds are concentrated in the upper atmosphere.

• Like Uranus, Neptune’s interior is made of rocky core surrounded by ice, water, ammonia and methane ice. There may be an ocean of super-hot water below the clouds.

• Originally classified as a planet, Pluto was reclassified as a dwarf planet when similar bodies were discovered in the Kuiper Belt. It has a complex terrain with mountains and ice plains.

• The Kuiper Belt is a ring beyond Neptune’s orbit containing icy objects. It formed from debris after the giant planets migrated outwards. It contains dwarf planets like Pluto and potentially millions of icy bodies.

Here is a summary of the key points about stars from the provided information:

• Stars shine due to nuclear fusion reactions in their cores, where hydrogen is fused into helium and releases energy. This fusion is powered by the intense heat and pressure from gravity.

• Stars are classified based on their properties like temperature, luminosity and composition using the Hertzsprung-Russell diagram which plots these factors.

• Main sequence stars on the diagonal band of the diagram are fusing hydrogen and include spectral types O, B, A, F, G, K, M from hottest to coolest.

• Stars have layered structures with nuclei, radiative and convective zones, photosphere, chromosphere and corona. Energy generated in the core moves outward through these layers.

• Nuclear fusion in stars occurs in step-wise processes, eventually producing heavier elements up to iron. These elements were formed over billions of years.

• The Sun will take about 10 billion years to use up all its hydrogen fuel through nuclear fusion, powering it for most of its lifetime on the main sequence.

Here is a summary of key points about nebulae:

• Nebulae are giant clouds of dust and gas in space. They form when sparse material in space clumps together through mutual gravitational attraction.

• Diffuse nebulae are categorized into emission nebulae, reflection nebulae, and dark nebulae based on how we see them from Earth.

• Emission nebulae emit radiation from ionized gas. Reflection nebulae reflect light from nearby stars. Dark nebulae contain darker groupings of dust that absorb light.

• Many nebulae are stellar nurseries where new stars are born inside dense clouds of material. The Eagle Nebula contains famous pillars of gas and dust where star formation is occurring.

• Planetary nebulae and supernova remnants are types of nebulae associated with dying and exploding stars. Planetary nebulae are formed from material expelled by aging stars, while supernova remnants are debris from exploded stars.

• The largest nebula on record is the Tarantula Nebula, which stretches over 1,800 light years in the Magellanic Cloud. Nebulae come in all different shapes and sizes.

Here is a summary of key points about nebulae and star clusters:

• A nebula is a large cloud of dust and gas in space. Reflection nebulae glow because dust reflects the light of nearby stars. Emission nebulae glow because the gas they contain is ionized by ultraviolet radiation from hot, young stars.

• Supernova remnants form when a massive star explodes violently in a supernova, sending a vast cloud of ionized dust and gas out into space. The Crab Nebula is the remnant of a massive star that exploded in 1054 CE.

• Star clusters are groups of stars that were formed from the same giant cloud of gas and dust. Open clusters are loosely bound groups of young stars, while globular clusters are giant balls of ancient stars tightly bound by gravity.

• The Pleiades is a famous open cluster visible to the naked eye consisting of around 3000 stars that are less than 100 million years old.

• Blue stragglers are unusually young, blue stars found in ancient globular clusters. They are thought to form when two old red stars collide and merge.

Here is a summary of the key points about n from Earth, sextenary systems:

• A sextenary system is a star system with six components (stars or planets).

• Earth is part of a sextenary system with the Sun and five other planets (Mercury, Venus, Mars, Jupiter, Saturn).

• The planets orbit the Sun in roughly circular orbits, with Earth’s orbit being approximately 150 million km from the Sun.

• Studies of sextenary systems can provide insights into how planetary systems form and evolve over long periods of time. Understanding our own solar system’s configuration and history as a sextenary system helps inform models of exoplanetary system formation.

• The six-body problem in celestial mechanics seeks to calculate the motions of objects within a sextenary system under the combined effects of their mutual gravitational attractions. Exact solutions are not possible so numerical methods are used.

• Our solar system’s status as a stable sextenary system over billions of years suggests the presence of five or six similarly-sized objects can lead to a long-lived planetary architecture, something exoplanet scientists are exploring.

• The four key ingredients for life are water, organic molecules, energy, and time. Water is essential for chemical reactions and life processes. Organic molecules like carbon are needed to form the building blocks of life.

• Life requires an energy source like sunlight. The Miller-Urey experiment in 1952 showed that lightning could provide energy for simple organic molecules to form from inorganic materials.

• Astrobilogists search for conditions that could support life on other worlds, like Saturn’s moon Enceladus which has subsurface oceans heated by tidal forces. Water plumes erupting from its icy surface contain organic molecules.

• With sufficient time, simple single-celled life can evolve into complex multicellular organisms. Life on Earth may have begun over 4 billion years ago.

• Organic molecules are abundant in space and found in meteorites, indicating they are common throughout the universe. So with the right ingredients and conditions, life could exist beyond Earth. The universe is vast so it is possible similar conditions that created life here also exist elsewhere.

• When low- and medium-mass stars like the Sun run out of hydrogen in their cores, they enter the red giant phase late in their lives.

• The core contracts and heats up, while hydrogen fusion begins in a shell surrounding the core. This dumps helium into the core and causes the star to expand greatly, becoming 100-1000 times the size of the Sun.

• The rising surface temperature makes the star glow red. Helium fusion then begins violently in the core through the triple-alpha process, producing carbon and oxygen.

• Eventually all the core’s fuel is exhausted. For the Sun, it will become a red giant in about 5 billion years, potentially engulfing Mercury, Venus, and maybe Earth before shrinking again.

• Medium-mass stars like the Sun end their lives as faint planetary nebulae that gradually fade, leaving behind white dwarf stars.

• White dwarfs are very dense, about the size of Earth but containing the same mass as the Sun. Their interiors are crystallized carbon and oxygen while their atmospheres are hydrogen or helium.

• Enormous gravitational pressure squeezes the electrons and atomic nuclei extremely close together in a state called “degenerate matter.” This pressure balances gravity and prevents further collapse.

• There is a limit to how much mass a white dwarf can have before exceeding the Chandrasekhar limit and causing gravitational collapse. Beyond about 1.4 solar masses, it will explode as a supernova.

• White dwarfs slowly cool over billions of years as they radiate away their thermal energy into space. Some have been observed destroying orbiting planets via their intense gravity over timescales of days to weeks.

• Stars with approximately 1.4 times the mass of the Sun or greater will eventually collapse and explode as a supernova after they have exhausted their nuclear fuel.

• This leaves behind either a neutron star or black hole. Neutron stars are the collapsed core that remains after the supernova explosion. Black holes would form if the core was even more massive.

• During the explosion, elements heavier than iron are produced through nuclear fusion and scattered across space. This includes many elements important for life like carbon and oxygen. Supernovae are therefore important in distributing metals throughout the universe.

• The explosion is triggered by the core collapsing in on itself very rapidly once nuclear fusion can no longer generate enough outward pressure to balance the inward force of gravity. This causes a massive shockwave that ejects the outer layers of the star.

Here is a summary of the key points about ole or a neutron star depending on the star’s mass:

• A neutron star forms when the core of a massive star collapses after the star dies in a supernova explosion. Only stars larger than around 8-10 times the mass of the Sun can form neutron stars.

• Neutron stars are incredibly dense, with a mass slightly greater than the Sun’s compressed into a sphere only around 20 km wide. This makes them one of the most dense objects in the universe.

• Neutrons stars are composed almost entirely of neutrons packed tightly together. They have intensely strong gravitational and magnetic fields.

• As neutron stars spin rapidly and have strong magnetic fields, some emit beams of electromagnetic radiation from their magnetic poles. When these beams sweep across the Earth, they appear as pulsating radio sources known as pulsars.

• If the collapsing stellar core is between 2-3 solar masses, it will collapse to form a neutron star. Anything larger than around 3 solar masses will continue collapsing to form a black hole.

Here is a summary of the key points about the structure of the Milky Way galaxy:

• It is a typical spiral galaxy with a central bulge or nucleus, two major spiral arms (Scutum-Centaurus and Perseus), and a spherical halo of stars surrounding the disc.

• The central bulge contains a supermassive black hole. The spiral arms contain relatively high densities of gas, dust, and young, blue stars.

• The Sun is located about 26,000 light years from the galactic center, within the Orion Spur branch of the Orion Arm.

• The Milky Way consists of an inner stellar disc about 100,000-120,000 light years across surrounded by a spherical halo of older stars up to 170,000-200,000 light years in diameter.

• It contains between 100-400 billion stars held together by gravitational attraction within clouds of gas and dust.

• Spiral galaxies make up about two-thirds of all observed galaxies.

• They have a flattened disc containing stars, gas, and dust. This material is concentrated into spiral arms that rotate around a central bulge containing densely packed stars, sometimes in a barred shape.

• The spiral arms contain many young, blue stars still forming. The central bulge contains older, redder stars.

• Spiral structure is thought to be caused by density waves propagating through the disc, triggering star formation as they pass.

• Our Milky Way galaxy is a barred spiral galaxy, as is the similarly shaped Andromeda Galaxy. Other notable spirals include the Whirlpool Galaxy and Pinwheel Galaxy.

• Interactions with neighboring galaxies can distort spiral structure through tidal forces. Mergers may transform spiral galaxies into elliptical galaxies over time.

• Spiral galaxies contain yellow stars in a broad, spherical halo and in globular star clusters located in the halo. They also contain stars forming spiral arms that rotate around the central nucleus.

• The nucleus contains the oldest stars orbiting in the central bulge around the central black hole.

• Spiral arms originate from density waves in the galactic disc and contain mainly young, blue stars. Gas and dust enter the arms and form new stars.

• Elliptical galaxies are spherical and contain older, yellow and red stars in randomly oriented orbits. They have little dust or gas and minimal new star formation.

• Lenticular galaxies have properties of both elliptical and spiral galaxies, containing a disc of stars, dust and gas flattened into a lens shape.

• Dwarf galaxies are much smaller than the Milky Way, typically containing less than a few billion stars, and orbit larger galaxies. Many have irregular shapes rather than defined spiral or elliptical structures.

• Some dwarf galaxies move independently while others are found in isolation between galaxy clusters.

• Dwarf galaxies are thought to have formed early in the universe, producing some of the first stars before merging to form larger galaxies.

• There are about 60 dwarf galaxies near the Milky Way, with the largest being the Large and Small Magellanic Clouds.

• Dwarf galaxies can have irregular, elliptical, spiral or barred spiral structures but their shapes are often disrupted by interactions with larger galaxies.

• Galaxy collisions are common in galaxy clusters and can stimulate star formation while also playing a role in galaxy evolution through gravitational disruption and pulling material into central black holes.

• Galaxy collisions are key to the transformation of galaxy types through mergers and interactions. Collisions can distort galaxies beyond recognition or cause one galaxy to engulf another.

• Computer simulations are used to model galaxy collisions over millions of years since they cannot be directly observed. Simulations show how galaxy structure is disrupted and transformed over time during mergers.

• Mergers are important in the theoretical model of galaxy evolution. According to this model, galaxies undergo a series of mergers that consume their gas and eventually form giant elliptical galaxies dominating galaxy clusters.

• Simulated collisions between large galaxies can generate thousands of times the sun’s mass in new stars every year as a result of the collision.

• Galaxies are often found in groups, clusters, and superclusters due to gravitational attraction. Collisions and mergers in clusters lead to larger galaxies and a predominance of elliptical galaxies over time.

The passage describes how we may be surrounded by a “sea” of WIMPs (Weakly Interacting Massive Particles), which are a proposed type of particle that could make up dark matter. Some key points:

• WIMPs are called this because they are hypothesized to barely interact with light or normal matter at all. They would pass through ordinary matter with little effect.

• WIMPs are a theoretical form of “cold dark matter”, meaning they would be relatively slow-moving particles.

• If WIMPs exist as theorized, they could make up a significant amount of the total matter in the universe. We may be entirely immersed in a “sea” of these particles, but unable to detect them directly due to their extremely weak interaction with normal matter and light.

• WIMPs are one of the primary candidates scientists have proposed for what might constitute dark matter, the unknown type of matter that accounts for the majority of matter in the universe but does not emit or interact with light.

So in summary, it speculates that dark matter could be composed of countless very low-interaction particles called WIMPs that permeate the universe but are nearly impossible to detect directly with current technology.

• According to Einstein’s general theory of relativity, spacetime is warped or curved by massive objects. The more mass an object has, the more it warps spacetime.

• Gravity is a result of these distortions in spacetime - objects follow curved paths in warped spacetime, giving the illusion of an attractive gravitational force.

• Examples given are Earth orbiting the Sun along a curved path in spacetime and light being bent around massive objects like the Sun.

• Gravitational waves were predicted by Einstein and have since been detected, providing evidence that spacetime can ripple or vibrate from events like black hole collisions.

• Looking into deep space means looking back in time, as light from distant galaxies was emitted long ago and is just now reaching us. The most distant galaxies seen with telescopes reveal what the early universe looked like billions of years ago.

• Particle accelerators can be used to simulate conditions in the early universe shortly after the Big Bang by smashing subatomic particles together at high energies.

• The early, opaque universe became transparent to light around 380,000 years after the Big Bang, allowing the cosmic microwave background radiation to travel freely - this provides a window into the oldest observable era.

• When astronomers plot the velocity of galaxies away from Earth against their distance, it produces a straight line. The slope of this line gives the Hubble constant, which measures the rate of expansion of the Universe.

• A straight line indicates that galaxies are receding from Earth at a rate proportional to their distance. The farther away a galaxy is, the faster it is receding due to the expansion of the Universe.

• By determining the slope of the line, astronomers can calculate the Hubble constant, which provides a measurement of how fast the Universe is expanding at the present day. Looking back in time, the Universe was smaller and expanding more rapidly in the past.

• Plotting velocity versus distance in this way helped establish evidence that the Universe is expanding and led to calculations of parameters like the Hubble constant that give insight into the age and evolution of the cosmos.

Here is a summary of the key events described:

• Shortly after the Big Bang, the first particles emerged from a sea of energy. Protons, neutrons, electrons, positrons, and other fundamental particles began to form.

• Within 20 minutes, the first atomic nuclei had formed as protons and neutrons combined. Matter and antimatter in the form of particles and antiparticles were both present.

• It took until around 380,000 years for the universe to cool enough for electrons to combine with atomic nuclei, forming the first atoms during the process of recombination. This included hydrogen, helium and lithium atoms.

• There was initially an equal amount of matter and antimatter created. However, for an unknown reason, there was a slight excess of matter over antimatter. The matter and antimatter largely annihilated each other, leaving a small residue of matter which now makes up the visible universe.

• The future of the universe depends on whether the gravitational attraction between celestial objects can be overcome by dark energy.

• Dark energy is a mysterious substance that acts in opposition to gravity and causes the expansion of the universe to accelerate. As the universe expands, there is more space so the effect of dark energy grows.

• If dark energy continues to dominate over gravity, the universe will expand forever in an “open universe” scenario.

• If gravity wins out, the universe could eventually collapse back in a “Big Crunch,” reversing the Big Bang and leading to a potential new Big Bang.

• Other possibilities include the heat death of the universe as galaxies, stars, and other celestial objects fade away over trillions of years or a rip in the fabric of spacetime caused by rapid expansion.

• The ultimate fate of the universe is still uncertain and depends on understanding the nature of dark energy and whether new physics theories could change expectations. Astronomers are still working to determine which scenario our universe is following.

Here is a summary of the key points about rockets from the passage:

• Rockets work by ejecting exhaust particles at high velocity in the opposite direction of the thrust, causing the rocket to move in the opposite direction due to Newton’s Third Law of Motion.

• The exhaust is produced by combustion of propellant like liquid or solid fuel and an oxidizer. Liquid fuel rockets use pumps to deliver propellants to combustion chambers while solid fuel rockets contain propellants in a solid casing.

• Multistage rockets are able to travel farther by jettisoning empty stages after they are used up. This reduces the mass being carried and increases the payload mass that can be delivered.

• Common liquid propellants are liquid oxygen and liquid hydrogen. Solid rockets often use ammonium perchlorate as an oxidizer and an organic polymer as fuel.

• Efficient combustion requires precisely mixing fuel and oxidizer. Liquid rockets enable more control over the rate of combustion. Solid rockets combust at a fixed rate determined by their chemical makeup.

• Rocket nozzles accelerate and direct the exhaust for thrust. Aerodynamic shapes like nose cones reduce air resistance during launch. Fairings protect payloads during launch through the atmosphere.

Here is a summary of the key points about satellite orbits:

• Satellites follow various orbits depending on their purpose, including low Earth orbit, geostationary orbit, elliptical orbit, etc.

• Orbits can be circular or elliptical in shape. Elliptical orbits cause the satellite’s speed to vary depending on its distance from Earth.

• Polar orbits allow satellites to view different bands of Earth’s surface with each orbit. Sun-synchronous orbits provide consistent lighting.

• Satellites in low Earth orbit orbit move faster than those in higher orbits due to their closer proximity to Earth.

• Geostationary orbit matches Earth’s rotational period, allowing satellites to remain fixed over one position on the equator.

• Multiple satellites can work together in coordinated patterns called constellations to provide continuous global coverage. Examples include GPS and satellite phone networks.

• Orbital altitude and inclination affect the satellite’s speed, coverage area, and amount of Earth’s surface it can view during each orbit.

According to the passage, the first satellite to orbit Earth was Sputnik, launched by the Soviet Union in 1957. Some key details:

• Sputnik’s orbit ranged from 215 to 939 km above Earth, and was tilted at 65° to the equator.

• The idea of using a satellite to relay communications signals in a geostationary orbit was proposed by Arthur C. Clarke in 1948, although he thought it would need to be a crewed space station rather than an unmanned satellite.

• The passage doesn’t provide many details about Sputnik itself, but focuses more on describing how satellite orbits have evolved and the variety of roles that satellites now fulfill, such as communications, navigation, weather monitoring, earth observation, etc.

So in summary, the first satellite to orbit Earth was Sputnik, launched by the Soviet Union in 1957, which paved the way for the development of satellites for a wide range of applications. The idea of using satellites for communications specifically was first proposed by Arthur C. Clarke.

• Satellites carry a wide variety of sensors like spectrometers, radar, infrared cameras, etc. to study Earth’s atmosphere, oceans, geology, land use, archaeology, and more.

• Some early applications of satellite imagery include discovering previously unknown Egyptian pyramids and monitoring large-scale weather patterns.

• Space telescopes in low Earth orbit as well as more distant orbits have capabilities that ground-based telescopes lack, like observing wavelengths blocked by Earth’s atmosphere.

• Observatories at Lagrangian points have advantages like shielding from Earth/Sun radiation and a fixed orientation relative to them. Examples include satellites at L1, L2 points.

• The Hubble Space Telescope is a reflecting telescope in low Earth orbit that has been serviced multiple times to replace instruments and parts. It produces high-quality images of distant stars and galaxies.

• Other space telescopes study high-energy phenomena like X-rays, gamma rays using specialized designs like grazing-incidence mirrors due to interactions of these wavelengths with normal mirrors.

• The Hubble Space Telescope (HST) revolutionized our understanding of the universe by taking high-quality images from its location in low Earth orbit, unhindered by the Earth’s atmosphere.

• It has been serviced and upgraded five separate times by Space Shuttle missions, most recently in 2009 before the Shuttle’s retirement.

• HST can detect invisible infrared and ultraviolet radiation that reveals hot or cool objects not visible in regular light.

• Data is stored on the telescope and downloaded to satellites every 12 hours for transmission to ground stations.

• Scientists use powerful computers to decode, process and analyze the raw data to produce images and information.

• HST’s images can rival those from much larger ground telescopes thanks to its location above the atmosphere.

So in summary, the Hubble Space Telescope has transformed astronomy through its unique position and ability to observe in non-visible wavelengths, obtaining extremely detailed images through multiple upgrade and servicing missions. Its data is carefully managed and analyzed to maximize scientific insights.

Crewed spaceflight involves spacecraft that carry astronauts and must keep them alive during missions. Key components include life support systems to provide breathable oxygen, drinkable water, and remove carbon dioxide waste. The spacecraft also needs pressure vessels, thermal protection, and other safety equipment for launch, time in space, and the hazardous re-entry process when temperatures can reach over 1500°C.

Some of the major crewed spacecraft programs include Soyuz, which has launched over 140 times from Russia since the 1960s; Apollo, which took US astronauts to the Moon from 1968-1975; Shenzhou from China since 2003; and Orion being developed by NASA for missions from 2023. These vehicles consist of modules for tasks like orbiting, re-entry, and crew habitation. Parachutes and water landings are commonly used for skip protection on return to Earth from low orbit.

The passage summarizes the key events of the Apollo missions to land astronauts on the Moon between 1969 and 1972. It describes:

• The complex three-part spacecraft (Command Module, Service Module, Lunar Module) used for the missions, launched by the Saturn V rocket.

• The approach taken for landing - using the Lunar Module to land on the Moon while keeping the Command and Service Module in lunar orbit for return.

• The different stages of launching from Earth orbit, flying to the Moon, landing on the Moon, exploring the surface, launching from the Moon back to lunar orbit, and returning to Earth splashdown.

• Some key details of the landing process and use of the Lunar Roving Vehicle on later missions. In total, the six Apollo missions returned 382 kg of lunar rock samples.

Here is a summary of key points about lunar landings and space stations:

• Only four Apollo missions (numbered 7-10) flew test missions before the moon landing to work out issues with the spacecraft in Earth and lunar orbit.

• The lunar roving vehicle was key to extending the range of exploration around the landing site. It was lightweight but robust and could carry twice its weight at a top speed of 11 mph.

• The International Space Station is the largest space station ever built and orbits low Earth orbit. It has living and working modules from several countries.

• Space shuttles were used to deliver components and link them together using robotic arms. Crews stay for about 6 months.

• Valery Polyakov holds the record for longest continuous time in space at 438 days on the Russian Mir space station from 1994-1995.

• Early Russian Salyut space stations in the 1970s tested basic designs for long-term habitation. Skylab was the USA’s first space station launched in 1973.

• Key modules on the ISS include laboratories, living quarters, robotic arms, airlocks for spacewalks, and solar panels for power. It has been continually crewed since 2000.

Voyager 1 did not visit Uranus and Neptune because it did not have enough fuel left after its encounters with Jupiter and Saturn. The trajectory required for the gravitational slingshot maneuvers to reach Uranus and Neptune would have left Voyager 1 without enough fuel to perform science observations at those destinations. Voyager 2 was launched a few weeks after Voyager 1 on a different trajectory that enabled it to visit Uranus and Neptune.

to utilize a planet’s gravity to

Spacecraft approaching

gain speed and change its

behind planet gains

flight path towards the

speed and changes

next destination.

trajectory

GRAVITATIONAL ASSISTS

Jupiter

Saturn

1979

1980-81

3 assists

2 assists

Uranus

Neptune

1986

1989

1 assist

1 assist

The key to the grand

Voyager 2 was launched just

tours of the outer planets

17 days after Voyager 1 on a

was careful timing so

trajectory designed to take

each planetary encounter advantage of gravitational

Voyager trajectories

provided enough of a

slingshots from Jupiter,

boost to reach the next.

Saturn, Uranus and Neptune.

Voyager 2 Jupiter

1976

Saturn

1980-81

Uranus

1986

Neptune

1989

SPACE EXPLORATION

Pluto and beyond

Voyager 1 and 2 launched in 1977, Voyager 2 left Earth just three weeks

on what became known as the

after Voyager 1. But by taking a longer path through the outer solar system it

“Grand Tour” of the outer planets. was able to use gravity assist maneuvers to visit Uranus and Neptune.

Why did Voyager 1 stop its outward

journey after Neptune?

Voyager 1 was launched on a faster trajectory than Voyager 2 and passed within 77,000 km of Jupiter in 1979, gaining a gravity assist boost to reach Saturn in 1980-81. After exploring Saturn, it received one final slingshot to send it on an escape path out of the solar system. Voyager 2 visited Jupiter in 1979, Saturn in 1981, Uranus in 1986 and Neptune in 1989 before also leaving the solar system.

Voyager 1’s faster path meant it did not have enough remaining fuel to slow down enough for a Uranus-Neptune trajectory after Jupiter and Saturn. Voyager 2 was launched on a slower trajectory that used gravity assists more efficiently to explore the outer planets before also leaving our solar system.

Spacecraft like Voyager have finite onboard fuel supplies. Using the optimal planetary encounter sequences maximized the science return for both missions within these constraints. Voyager 1’s journey took it on the first human mission to interstellar space.

210-211_Voyager_Grand_Tour.indd 210

Photograph of the planets taken by Voyager 1 from 4 billion km away

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SPACE EXPLORATION

Pluto and beyond

POSSIBLE VOYAGER

Following its Neptune flyby in 1989, Voyager 2 had enough fuel remaining to consider targeting Pluto as well. However, Pluto was even farther away. At its maximum distance from Earth, Pluto would have added over 10 years to Voyager 2’s travel time, requiring it to operate flawlessly far beyond its design lifetime. The spacecraft would have arrived in the late 1990s when Pluto was on the opposite side of the Sun from Earth, making communications very challenging. In the end, NASA chose to use Voyager 2’s remaining capabilities for more immediate solar system exploration rather than bet on such an ambitious long-term mission. Later Pluto missions were left to purpose-built spacecraft like New Horizons.

TRAJECTORY TO PLUTO

EARTH

JUPITER 1979 SATURN 1980-81 URANUS 1986

NEPTUNE 1989

VOYAGER 2 Maximum distance from Earth

PLUTO (Late 1990s)

On the other side of the Sun

INTERSTELLAR SPACE

Despite not visiting Pluto, both Voyager spacecraft are still operating and have become the first human-made objects to reach interstellar space, entering regions between the stars. They continue transmitting data about conditions at the edge of our solar system’s influence as they journey on through the Milky Way galaxy. Their extraordinary durability has allowed insights no mission could have envisioned at their launch over 40 years ago.

210-211_Voyager_Grand_Tour.indd 211

Successful missions to Pluto

NASA’s New Horizons spacecraft visited Pluto in 2015, returning the first close-up images. Launched in 2006, it was designed specifically for the long-distance Pluto flyby mission. The European Space Agency’s BepiColombo mission, en route to Mercury, performed a gravity assist flyby of Pluto in 2015 to gain a slingshot trajectory boost.

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SPACE EXPLORATION

Orbital mechanics

WHY DO SATELLITES

Orbital mechanics is the application of Newtonian physics to predict the motions of artificial satellites and space vehicles. Understanding orbital mechanics enables spacecraft to be precisely positioned and maneuvered through controlled propulsion.

ORBIT THE EARTH IN

CIRCULAR ORBITS?

Earth’s gravity pulls satellites into elliptical orbits. However, circular orbits offer advantages like:

Elliptical orbit

• Consistent altitude above any location facilitates communication coverage.

• Predictable flight path simplifies rendezvous/docking with other spacecraft.

• Fuel efficiency - less propellant needed for stationkeeping compared to elliptical orbits.

• Stress/wear reduction - no high/low points in orbit to endure as in elliptical orbits.

• Suitable for constellations providing continuous global coverage like GPS, communication/imaging satellites.

GEOSTATIONARY ORBIT

A circular geostationary orbit exactly matches the Earth’s rotation period of 24 hours. Satellites in this orbit appear stationary from Earth’s surface, making them ideal for applications like TV/radio broadcasting, weather monitoring.

LEO, MEO, HEO

Most telecoms, Earth observation and manned satellites operate in circular low Earth orbits (LEO<2000km), medium Earth orbits (MEO 2000-35786km) and high elliptical orbits (HEO crossing LEO and GSO).

Circular orbit

Earth Centric view Earth Surface view

Geostationary orbit

(appears stationary from Earth)

Low Earth orbits (LEO)

Medium Earth orbits (MEO)

Highly elliptical orbits (HEO)

SPACE EXPLORATION

Earth observation

EARTH OBSERVING SATELLITES perform essential scientific roles by continuously monitoring environmental factors like weather, ocean conditions, agriculture, natural disasters, land use, and more. They provide a global view of our planet unavailable from ground-based systems alone.

WHY IS IT DIFFICULT FOR

SATELLITES TO OBSERVE

THE POLAR REGIONS?

Satellites in low Earth orbit travel North to South, parallel to the equator. This results in:

• Polar regions only being observed a couple times per day, compared to numerous passes over equatorial areas.

• Oblique viewing angles that can distort observations and reduce spatial resolution near the poles.

• Increased atmosphere between satellite and surface at high latitudes introducing more scattering/absorption effects.

To address this, dedicated polar-orbiting satellites are launched at higher, Sun-synchronous altitudes of ~800-850km where their orbit precesses to maintain an angle to the Sun. This provides multiple daily views of polar zones at consistent local times, important for applications like weather monitoring. Some high-inclination LEO satellites like Sentinel-2 also directly image polar territories on each orbit.

Polar orbiting satellite view

Equatorial satellite view

The inclined orbit of polar satellites provides better coverage near the poles compared to satellites following equatorial orbits. Their higher altitude also reduces distortions from the oblique viewing angle, important for applications like measuring sea ice extent.

SPACE EXPLORATION

Solar system exploration

MARS EXPLORATION ROVERS Examples of Mars observations by NASA’s rovers:

Spirit (2004-2010) and Opportunity (2004-2018) made surprising discoveries of ancient environments capable of supporting microbial life, such as sedimentary rock formations suggestive of standing bodies of water. Chemical and mineralogical analyses provided evidence the sites experienced interactions between water and rock chemistry.

Curiosity (since 2012) found an ancient freshwater lake with chemical building blocks for life within 3 billion years of Mars’ formation, including complex organic compounds in sedimentary rocks. Its precision drilling and sample analysis confirmed the Gale Crater site transitioned from a lake bearing clay minerals to drier conditions with sulfate minerals.

Perseverance (launched 2020) will search for biosignatures of ancient microbial life at Jezero Crater, a lake-river-delta system on Mars billions of years ago. Its groundbreaking instruments include MOXIE to demonstrate production of oxygen from Martian atmosphere, and systems to core and cache rock/regolith samples for potential future return to Earth.

Why is Mars considered the Most astrobiologically promising destination for future exploration?

Mars is considered the most promising destination for astrobiology because it had liquid water on its surface in the past - a key requirement for the development of life as we know it. Strong geological evidence from Mars rovers and orbiters shows some regions on Mars had stable environmental conditions conducive to microbial life billions of years ago, including lakes, rivers and possibly oceans. Although Mars is now cold and dry, returning samples from sites where ancient water was present has the potential to reveal if life ever arose on Mars. This would transform our understanding of life’s origin and distribution in the universe.

The key factors that make Mars scientifically compelling are:

• Geological evidence for long-term stable surface water in Mars’ ancient past
• Relatively recent water-rock interactions up to 3 billion years ago in the geologic record
• Accessibility to samples from this time period for analysis on Earth
• Lower danger of contaminating Earth with any potential Martian lifeforms compared to other targets like Europa or Enceladus under ice shells

Assuming life originated early in Solar System history, Mars represents humanity’s best chance of finding evidence of life beyond Earth with the exploration capabilities available today. Finding life on Mars would suggest life may be ubiquitous in the universe.

SPACE EXPLORATION

Space telescopes

WHY IS THE JAMES WEBB

Space telescopes like Hubble, Spitzer, Chandra and Kepler/TESS have revolutionized astronomy by making observations impossible from Earth’s surface. The James Webb Space Telescope will build on this legacy with even greater capabilities:

SPACE TELESCOPE BEING

LAUNCHED ON AN ARIANE 5

• Located at Sun-Earth Lagrange point 2, 1 million km from Earth, it will have a large 6.5m primary mirror able to capture faint infrared light from the first galaxies to form after the Big Bang.

ROCKET?

• Its infrared cameras and spectrographs will look through cosmic dust to study the birth of stars and protoplanetary systems.

• A 5-layer sunshield the size of a tennis court will shield the mirrors and instruments at -233°C to enable high sensitivity infrared observations.

• Delicate deployment of the mirror and sunshield in space is required, ruling out the less powerful Delta IV Heavy usually used by NASA.

The Ariane 5 was selected as its launch vehicle because it can carry the over 6 tonne JWST to its operational orbit in one launch, without the need for assembly. Its significant payload capacity and proven reliability make it well suited for this challenging deployment. JWST will be placed at the second Earth-Sun Lagrange point for thermal stability and to stay in line-of-sight with Earth for communications. Its unprecedented capabilities will allow insights into the earliest galaxies, formation of star systems, and the composition of exoplanet atmospheres.

SPACE EXPLORATION

The search for life

EXOPLANET DISCOVERY METHODS

Transit Method - Detects dimming of star’s light as planet passes in front. Indicates planet’s size relative to star.

Radial Velocity Method - Measures star’s “wobble” caused by planet’s gravitational tug, revealing planet’s mass & orbital elements.

Direct Imaging - Immediate photography of exoplanet, though currently limited to young, massive planets far from host star.

Gravitational Microlensing - Detection of light magnification when a planet passes near the line-of-sight of a more distant background star.

Astrometry - Precise positional measurements of star reveal movement induced by planetary companion’s gravity.

CHARACTERIZING EXOPLANET ATMOSPHERES

Transmission Spectroscopy - Analyzes starlight filtering through planet’s atmosphere during transits for chemical fingerprints.

Emission Spectroscopy - Detects infrared light directly emitted or reflected from planet for composition clues.

Polarimetry - Measures how scattered starlight becomes polarized after interacting with a planet’s atmospheric gases.

Why is studying exoplanet atmospheres important for the search for life?

The atmospheres of exoplanets provide a direct window into their chemistry and potential habitability. Detection of biomarkers like oxygen, methane, ozone in coherent combination could indicate biological activity is altering an atmosphere. In our Solar System, Earth stands out for having abundant life and a biosignature atmosphere in chemical disequilibrium. Finding a similarly “non-equilibrium” exoplanet atmosphere would motivate future observations searching for signs of photosynthesis or metabolism on the planetary surface below. Characterizing atmospheres is a crucial step toward identifying potentially habitable exoplanets and worlds where trace evidence of life processes may one day be found.

SPACE EXPLORATION

Space activity challenges

CHALLENGES OF SPACE ACTIVITY

• Cost and complexity: Space travel requires advanced technology and substantial funding for development, launch and operations.

• Launch risks: Rockets have a failure rate of around 2%, endangering expensive payloads and crews during critical launch and ascent phases.

• Radiation hazards: Space radiation exposure can increase long-term health risks like cancer for astronauts working outside low Earth orbit protection.

• Microgravity effects: Prolonged weightlessness has physiological impacts requiring mitigation strategies on long-duration missions.

• Resource limitations: Spacecraft have finite life support consumables, power and fuel that constrain mission durations and layouts.

• Communication delays: Light-speed lag between Earth and distant spacecraft complicates real-time control and monitoring.

• Debris hazards: Low Earth orbit is congested with orbital debris threatening collisions with operational satellites.

• Public perception: High profile failures can damage public trust and enthusiasm for human and robotic space programs.

ADDRESSING THESE CHALLENGES

International partnerships, commercialization, reusable launch systems and orbital debris mitigation are helping address these issues. Medical and materials research aims to safeguard astronaut health on deep space missions. Space activities will always carry risks, but past experience and ongoing improvements are enhancing safety and sustainability of expanding human presence beyond Earth.

WHY DOES SPACE JUNK

POSE A GROWING RISK TO

SPACE EXPLORATION?

As spaceflight has expanded since the 1950s, over 170 million pieces of debris smaller than 1cm and over 23,000 pieces larger than 10cm now orbit Earth. This provides serious risk of collisions that could damage or destroy orbiting spacecraft. Derelict objects travel at speeds of up to 28,000 km/h, enough to inflict catastrophic damage. Fragmentation events also generate new clouds of debris. Mitigation practices aim to limit debris generation through controlled re-entry of retired spacecraft. Active debris removal may one day address the worst offenders and curb growth of the population. But space junk poses an enduring management challenge as activities in Earth orbit proliferate.

SPACE EXPLORATION

Early rocket development

EARLY ROCKET PIONEERS

• Robert Goddard (1882-1945): First to demonstrate liquid propellant rocket in 1926. Developed multicell rocket in 1933 with fins. Published theories on rocket propulsion leading development.

• Hermann Oberth (1894-1989): Published theories on multistage rockets and astronautics in 1920s. Strongly influenced early rocket pioneers like Goddard and von Braun.

• Konstantin Tsiolkovsky (1857-1935): Russian pioneer theorized liquid- and solid-fueled rocket propulsion and multistage rockets, controlled flight and space stations. Published influential works in 1903.

• Sergei Korolev (1907-1966): Chief Soviet rocket engineer, led Soviet space program including Sputnik and first human spaceflight of Vostok. Developed R-7 intercontinental ballistic missile and its space versions.

• Wernher von Braun (1912-1977): Developed Nazi Germany’s V-2 rocket during WWII. Later led U.S. Army rocket team, designed Jupiter missiles and Saturn V moon rocket. Founding figure of NASA Marshall Space Flight Center.

ROCKET DEVELOPMENT MILESTONES

• 1926: Goddard flies world’s first liquid-propellant rocket for 2.5 sec at 126m altitude.

• 1942: German V-2 becomes first rocket to reach space at 86 km. Launch 4,000+ during WWII.

• 1950s: U.S. and USSR develop multi-megaton thermonuclear weapons on ballistic missiles.

• 1957: Soviet R-7 ICBM launches Sputnik, inaugurating Space Age.

• 1961: Yuri Gagarin becomes first human in space aboard Vostok 1.

• 1969: Saturn V launches Apollo 11 to the Moon.

WHAT WAS THE MAIN DRIVER

BEHIND EARLY ROCKET

DEVELOPMENT?

The main driver behind early rocket development during the first half of the 20th century was military applications, specifically rockets as weapons and ballistic missiles

Here is a summary of the key points about NASA’s Voyager spacecraft and their missions:

• Voyager 1 and 2 were launched in 1977 on a “Grand Tour” to explore the outer planets of the Solar System. Their trajectories took advantage of a rare alignment of the outer planets.

• Each spacecraft flew by Jupiter, Saturn, and in Voyager 2’s case, Uranus and Neptune, sending back the first close-up pictures and data from these planets.

• Voyager 1 encountered Saturn’s moon Titan in 1980 and was deflected out of the plane of the Solar System.

• The Voyagers continue to transmit valuable scientific data at the edge of the heliosphere, where the Solar wind meets interstellar space. They will continue operating until their power sources decay in the mid-2020s.

• The missions have provided humanity’s first detailed look at the giant outer planets and allowed ongoing study of conditions at the boundary of the Solar System. The Voyagers have thus transformed our understanding of the outer Solar System.

Here is a summary of the key points about New Horizons’ flyby of Pluto:

• New Horizons launched in 2006 on an Atlas V rocket, which gave it a gravity assist from Jupiter in 2007 to boost its speed. Then it entered hibernation mode until 2014 as it traveled to Pluto.

• In July 2015, New Horizons conducted a flyby of Pluto, coming as close as 3,500 km. It was traveling at over 52,000 mph.

• Its instruments included LORRI (long-range camera), Ralph (telescopic camera), and Alice (ultraviolet spectrometer). These mapped Pluto’s surface, gathered geological data, and analyzed its atmosphere and composition.

• After the Pluto flyby, NASA adjusted New Horizons’ path slightly so it could also fly by and image another Kuiper Belt object called Arrokoth in 2019, before it runs out of fuel.

• New Horizons continues to send back science data from the Pluto flyby over several months, as the large amount of data had to be transmitted slowly due to the vast distance from Earth.

Here is a summary of the key points from the topics provided:

• Ion 62 - Ions are charged atoms that play an important role in space weather. Solar winds deposit ions on planetary atmospheres and surfaces.

• Milky Way 128-29 - The Milky Way is a spiral galaxy containing over 100 billion stars. It has a supermassive black hole at its center, dark matter halo, and a bar structure that spans half its diameter.

• Chromatic aberration 23 - Chromatic aberration is the failure of a lens to focus all colors to the same point, producing colored fringes. It affects refracting telescope images and was first explained by Galileo.

• Air resistance 197 - Air resistance increases dramatically with speed and is a major challenge for atmospheric reentry of spacecraft. Heat shields are needed to protect against frictional heating from dense atmospheres.

• Sun 40, 41 - The Sun is a yellow dwarf star at the center of the Solar System. Its atmosphere includes the photosphere, the chromosphere that can be seen during total solar eclipses, and the million-degree corona.

• Titan 76, 77, 212 - Titan is Saturn’s largest moon, with a thick nitrogen-rich atmosphere and methane clouds and lakes on its surface. The Cassini mission revealed intricate surface features and complex methane-based hydrocarbon chemistry.

• Uranus 78 - Uranus is an ice giant planet with extremely cold atmospheric temperatures. It rotates on its side and has a system of rings. The Voyager 2 flyby in 1986 was the only close-up study of Uranus so far.

• Venis 52, 54-55 - Venus has a toxic 96.5% carbon dioxide atmosphere capable of a runaway greenhouse effect. Its surface is intensely hot due to the greenhouse effect. The Soviet Venera probes were the only successful landings, surviving only minutes on the surface.

• Atmospheric turbulence 24 - Turbulence in the Earth’s atmosphere causes stars to twinkle and limits ground-based telescope resolution compared to space telescopes. Adaptive optics and space telescopes help overcome this effect.

Here is a summary of the key topics from the passage:

• Ts 210: Refers to the Tunguska event in 1908, a large explosion in Siberia caused by a meteor or asteroid.

• Hoba meteorite 29: The largest known meteorite on Earth, located in Namibia. Weighs over 60 tons.

• Ion engines 63, 192–93: Spacecraft propulsion systems that accelerate ions to produce thrust. More efficient than chemical rockets.

• Exo-Earths 102: Potentially habitable exoplanets similar in size and temperature to Earth.

• Gravitational waves 121, 154–55: Ripples in spacetime predicted by Einstein and detected by LIGO in 2016, providing evidence of black hole mergers.

• Hot-Jupiters 65, 102: Large gas giant exoplanets closer to their stars than Mercury is to the Sun. They are very hot as a result.

• Hubble, Edwin 132, 139, 158: Astronomer who significantly advanced the study of the structure, content and evolution of the universe through his observations and theoretical work. Namesake of the Hubble Space Telescope.

• Hubble Space Telescope 137, 152, 156, 160, 188–89: NASA’s orbital telescope, launched in 1990 and still operational. Provided unprecedented deep views of the cosmos. Underscores the importance of space-based astronomy.

Here is a summary of the key sections in the document:

• The document provides an overview of space and our solar system. It starts with an introduction to astronomy and our place in the universe, then discusses the structure and formation of the solar system and the planets.

• It covers the different types of stars, how they form and evolve over their lifetime. This includes discussions of nebulae, supernovae and stellar remnants like white dwarfs and neutron stars.

• Galaxies and the wider universe are examined next, looking at our Milky Way galaxy and nearby galaxies, as well as galaxy types, clusters and the composition and expansion of the universe since the Big Bang.

• The final section discusses the history and technologies of space exploration, from early rockets to current and future robotic and crewed spacecraft. It covers satellites, the Space Shuttle, space stations and missions to explore the solar system.

• Other notable topics include spectroscopy, exoplanets, dark matter, and the possibility of life elsewhere in the universe. The document provides an overview of astronomy and astrophysics from the scale of our solar system to the entire observable universe.