Space Flashcards
What objects make up our Solar System?
Our Solar System consists of one star (the Sun), eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), dwarf planets (like Pluto, Ceres), moons, asteroids, comets, and other small bodies. All these orbit the Sun under its gravity.
In which galaxy is our Solar System located?
Our Solar System is part of the Milky Way galaxy, a vast collection of stars, dust, and gas held together by gravity.
The Milky Way contains billions of stars and their planetary systems.
What is a natural satellite?
A natural satellite is a celestial body that orbits a planet or dwarf planet. An example is the Moon (natural satellite of Earth) or Europa (satellite of Jupiter). Natural satellites are commonly called moons.
How did the Sun form?
The Sun formed from a large cloud of dust and gas (a nebula) about 4.6 billion years ago. Gravity caused the cloud to collapse and heat up. As the core got extremely hot and dense, nuclear fusion reactions of hydrogen into helium began. This release of energy created an outward pressure that balanced gravitational collapse, and a star (the Sun) was born.
What is nuclear fusion in a star? How does it create equilibrium?
Nuclear fusion is the process where atomic nuclei combine to form heavier nuclei, releasing energy. In a star’s core (like the Sun), hydrogen nuclei fuse into helium, releasing a huge amount of energy (light and heat). This energy produces an outward pressure. Equilibrium occurs when this outward pressure from fusion balances the inward pull of gravity. This balance keeps the star stable in the main sequence stage.
Describe the life cycle of a star like the Sun.
- Nebula (Protostar): A star begins as a collapse of a nebula (cloud of gas and dust). Gravitational collapse heats the core.
- Main Sequence: When core temperature is high enough, hydrogen fusion starts. The star enters the main sequence (like the current Sun), fusing hydrogen into helium steadily. It remains stable for billions of years as long as fuel lasts.
- Red Giant: When hydrogen in the core is nearly exhausted, the core contracts and heats up, causing the outer layers to expand and cool. The star becomes a red giant. Helium fusion may occur in the core to make carbon.
- Planetary Nebula: After helium is used up, the outer layers are expelled into space, leaving behind the hot core. This results in a glowing shell of gas known as a planetary nebula.
- White Dwarf: The remaining core cools and shrinks to a white dwarf, which will gradually cool over time.
In summary, Sun-like stars evolve: Nebula → Main Sequence → Red Giant → Planetary Nebula → White Dwarf.
Describe the life cycle of a star much more massive than the Sun.
- Nebula and Main Sequence: Like smaller stars, a massive star forms from a nebula and enters the main sequence, fusing hydrogen into helium. Massive stars burn hotter and faster.
- Red Supergiant: After exhausting core hydrogen, the star expands into a red supergiant. In the core and shells, heavier elements fuse (helium to carbon, carbon to oxygen, etc.), building layers like an onion.
- Supernova: When iron builds up, fusion stops (because forming heavier elements by fusion requires energy). The core collapses catastrophically, resulting in a supernova explosion, one of the most energetic events.
- Neutron Star or Black Hole: Depending on the remaining mass, the remnant core becomes a neutron star (if moderately massive) or collapses into a black hole (if extremely massive).
Summary: Nebula → Main Sequence → Red Supergiant → Supernova → Neutron Star/Black Hole.
How are new chemical elements formed in stars and supernovae?
- Stellar Fusion: In stars during their life (especially when large), nuclear fusion reactions build heavier elements from lighter ones: e.g., hydrogen fuses to helium, helium fuses to carbon/oxygen, etc., up to iron under extreme temperatures. Fusion releases energy and creates elements like carbon, oxygen, silicon, and so on.
- Supernova Nucleosynthesis: Elements heavier than iron (such as gold, uranium) are formed during supernova explosions. The supernova’s extreme energy and neutron flux allow rapid fusion (neutron capture) to create these heavy elements.
- Distribution: The supernova explosion disperses these newly formed elements into space. This enriches the interstellar medium with heavy elements, which can later become part of new stars and planets.
In summary, stars fuse elements up to iron; supernovae create and spread elements heavier than iron.
What force keeps planets and satellites in circular orbits?
Gravity provides the centripetal force that keeps planets orbiting stars and satellites orbiting planets. The gravitational attraction between two masses (e.g. Sun and Earth) causes the object to constantly change its direction, bending its path into an orbit. In a circular orbit, gravity continually pulls the satellite toward the center, perpendicular to its velocity, resulting in constant change of direction but constant speed.
How are planets, moons, and artificial satellites similar and different?
All three orbit under gravity: planets orbit a star (the Sun), natural satellites (moons) orbit planets (e.g. Earth’s Moon), and artificial satellites are man-made objects placed into orbit (around Earth or other bodies). Similarities: they all follow orbital paths determined by gravity and have tangential velocity. Differences: natural satellites are naturally occurring; artificial satellites are manufactured for communication, observation, etc. Planets are large enough to clear their orbits and often have no parent body besides the Sun; moons orbit planets; artificial satellites can orbit Earth (like the International Space Station) or other planets.
Explain how an object in a circular orbit can have constant speed but changing velocity.
In circular orbit, the object moves around at constant speed, but its velocity vector is constantly changing direction. Gravity acts at right angles to the object’s instantaneous motion (toward the center). This centripetal force changes the direction of velocity without changing its magnitude. Thus, the speed stays the same, but since velocity includes direction, the velocity is continuously changing.
What must happen to the radius of an orbit if an object’s speed changes?
For a stable orbit, speed and radius are related: if a satellite’s speed increases, it will move into a higher orbit (larger radius) to maintain stability; if its speed decreases, it will drop to a lower orbit (smaller radius). This is because the orbital velocity depends on radius. In general, a faster orbit requires a larger radius for the same gravitational force to provide the correct centripetal force.
What is red-shift?
Red-shift is the observed increase in the wavelength of light coming from an object (like a distant galaxy), which shifts the spectral lines toward the red end of the spectrum. It happens when an object is moving away from the observer (Doppler effect for light): the light waves are stretched, making them longer (redder).
What does the observed red-shift of galaxies tell us about their motion?
The red-shift shows that most distant galaxies are moving away from us. Moreover, the farther away a galaxy is, the larger its red-shift (its light is more shifted). This implies that distant galaxies are receding faster. This relationship (velocity proportional to distance) suggests the universe is expanding.
How does red-shift provide evidence for an expanding universe and the Big Bang theory?
- Observation: Astronomers observe that the spectral lines from most galaxies are shifted to longer wavelengths (red-shifted). This is interpreted as those galaxies moving away from us (Doppler effect for light).
- Hubble’s Law: The red-shift is larger for more distant galaxies, indicating that velocity of recession is proportional to distance. This means all galaxies are moving apart, not just locally but everywhere.
- Expansion of Space: If every galaxy is receding, it implies space itself is expanding. It’s like dots on an inflating balloon moving apart.
- Big Bang Implication: An expanding universe suggests that in the past, the universe was much smaller and denser. Working backwards, there must have been a hot, dense starting point – the Big Bang.
- Supporting Evidence: The cosmic microwave background and the distribution of elements also support this model. The observed expansion (red-shift) is a key evidence for the Big Bang theory.
- Current Research: Observations since 1998 (studies of distant supernovae) show the expansion of the universe is accelerating, implying a force (dark energy) driving it. Also, much of the universe’s matter is “dark” (unseen) but inferred by gravitational effects.
In summary, red-shift implies galaxies are receding, meaning an expanding universe, which is exactly what the Big Bang theory predicts.
What have observations since 1998 suggested about the expansion of the universe?
Observations of distant supernovae since 1998 have shown that the expansion of the universe is accelerating, not slowing. This surprising result suggests there is a mysterious dark energy causing the acceleration. It also means that standard Big Bang expansion is influenced by unknown factors.
What are dark matter and dark energy (in brief)?
Dark matter refers to unseen matter that does not emit light but whose presence is inferred from gravitational effects (e.g. galaxies rotate faster than visible mass suggests). Dark energy is a hypothetical form of energy that permeates space and causes the accelerated expansion of the universe. Both are not fully understood, but evidence (galaxy motions, cosmic expansion) shows they must exist to explain observations.
What objects make up our Solar System?
Our Solar System consists of one star (the Sun), eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), dwarf planets (like Pluto, Ceres), moons, asteroids, comets, and other small bodies. All these orbit the Sun under its gravity.
In which galaxy is our Solar System located?
Our Solar System is part of the Milky Way galaxy, a vast collection of stars, dust, and gas held together by gravity.
The Milky Way contains billions of stars and their planetary systems.
What is a natural satellite?
A natural satellite is a celestial body that orbits a planet or dwarf planet. An example is the Moon (natural satellite of Earth) or Europa (satellite of Jupiter). Natural satellites are commonly called moons.
How did the Sun form?
The Sun formed from a large cloud of dust and gas (a nebula) about 4.6 billion years ago. Gravity caused the cloud to collapse and heat up. As the core got extremely hot and dense, nuclear fusion reactions of hydrogen into helium began. This release of energy created an outward pressure that balanced gravitational collapse, and a star (the Sun) was born.
What is nuclear fusion in a star? How does it create equilibrium?
Nuclear fusion is the process where atomic nuclei combine to form heavier nuclei, releasing energy. In a star’s core (like the Sun), hydrogen nuclei fuse into helium, releasing a huge amount of energy (light and heat). This energy produces an outward pressure. Equilibrium occurs when this outward pressure from fusion balances the inward pull of gravity. This balance keeps the star stable in the main sequence stage.
Describe the life cycle of a star like the Sun.
- Nebula (Protostar): A star begins as a collapse of a nebula (cloud of gas and dust). Gravitational collapse heats the core.
- Main Sequence: When core temperature is high enough, hydrogen fusion starts. The star enters the main sequence (like the current Sun), fusing hydrogen into helium steadily. It remains stable for billions of years as long as fuel lasts.
- Red Giant: When hydrogen in the core is nearly exhausted, the core contracts and heats up, causing the outer layers to expand and cool. The star becomes a red giant. Helium fusion may occur in the core to make carbon.
- Planetary Nebula: After helium is used up, the outer layers are expelled into space, leaving behind the hot core. This results in a glowing shell of gas known as a planetary nebula.
- White Dwarf: The remaining core cools and shrinks to a white dwarf, which will gradually cool over time.
In summary, Sun-like stars evolve: Nebula → Main Sequence → Red Giant → Planetary Nebula → White Dwarf.
Describe the life cycle of a star much more massive than the Sun.
- Nebula and Main Sequence: Like smaller stars, a massive star forms from a nebula and enters the main sequence, fusing hydrogen into helium. Massive stars burn hotter and faster.
- Red Supergiant: After exhausting core hydrogen, the star expands into a red supergiant. In the core and shells, heavier elements fuse (helium to carbon, carbon to oxygen, etc.), building layers like an onion.
- Supernova: When iron builds up, fusion stops (because forming heavier elements by fusion requires energy). The core collapses catastrophically, resulting in a supernova explosion, one of the most energetic events.
- Neutron Star or Black Hole: Depending on the remaining mass, the remnant core becomes a neutron star (if moderately massive) or collapses into a black hole (if extremely massive).
Summary: Nebula → Main Sequence → Red Supergiant → Supernova → Neutron Star/Black Hole.
