Space Physics Flashcards
What is the relationship between the Earth and the Sun, and how does the Moon relate to the Earth?
- The Earth is a planet travelling in a nearly circular orbit around the Sun.
- The Moon orbits the Earth as a satellite.
How does the Earth move, and what does this motion cause?
Motion of Earth:
* The Earth spins about its axis (the line passing through the north and south poles) and makes one complete rotation every 24 hours. This causes day and night.
* The Earth’s rotation on its axis causes the Sun to have an apparent daily journey from east to west.
Why do seasons occur on Earth?
Seasons (Summer, Autumn, Winter, Spring) happen due to two factors:
* The rotation of Earth about the Sun once in 365 days (1 Year).
* The tilt of the Earth’s axis by 23.5° to the plane of its path around the Sun.
How long does it take for the Earth to orbit the Sun, and in what shape is this orbit?
The Earth orbits the Sun in approximately 365 days, and this orbit is nearly circular.
How long does it take for light from the Sun to reach Earth?
Light from the Sun takes about 500 seconds (around 8 minutes 20 seconds) to reach Earth.
What happens to day length on specific dates in the Northern and Southern Hemispheres?
Length of Days:
* The longest day for the Northern Hemisphere and the shortest day for the Southern Hemisphere is 21 June. (The Sun is highest above the horizon.)
* The longest day for the Southern Hemisphere and the shortest day for the Northern Hemisphere is 21 December. (The Sun is lowest above the horizon.)
How does the Moon move relative to the Earth, and what other properties does the moon have?
Motion of the Moon:
* The Moon is a satellite of the Earth.
* It rotates around Earth once every month.
* It rotates about its axis every month and always has the same side facing the Earth, so we never see the dark side of the Moon.
Other properties:
* It does not have an atmosphere.
* It has a low gravitational field compared with Earth.
What are the phases of the Moon, and why do they occur?
Phases of the Moon:
- In the new Moon phase, the Moon is between the Sun and the Earth, and the side facing the Earth is unlit, so it is not visible from the Earth.
- A thin new crescent appears along one edge as it travels in its orbit.
- The size of the crescent increases until it reaches the first quarter phase. In the first quarter phase, half of the Moon can be seen.
- At full Moon, the Moon is on the opposite side of Earth from the Sun and appears as a complete circle.
- After that, it wanes through the last quarter phase until only the crescent can be seen again.
- The Moon appears to have a daily trip across the sky, rising from east to west.
How can we calculate the average orbital speed of the Moon, and what do the symbols in the formula mean?
Orbital Speed: The average orbital speed. 𝑣 of the Moon is calculated by:
𝑣 =
* circumference / timeofonerotation
* 2𝜋𝑟 / 𝑇
where:
* 𝑟 is the radius of the orbit,
* 𝑇 is the time taken by the Moon to make one complete rotation around the Earth.
What does the Solar System consist of?
The Solar System:
* It consists of one star (the Sun) and eight planets moving around it in elliptical orbits.
* It includes dwarf planets and asteroids which orbit the Sun.
* Moons that orbit many planets.
* It contains comets and natural satellites.
What are the four inner planets, and what are their characteristics?
The Four Inner Planets: Mercury, Venus, Earth, and Mars. They are:
* Small in size
* Solid
* Rocky
* Have high density
What are the four outer planets, and what are their characteristics?
The Four Outer Planets: Jupiter, Saturn, Uranus, and Neptune. They are:
- Larger in size
- Colder
- Consist mainly of gases
- Have low densities
What is a dwarf planet, and can you give an example?
Dwarf Planets: For example, Pluto. They:
- Orbit the Sun at an average distance greater than Neptune.
What are asteroids, what are their characteristics, where are they mainly found, and what is a famous example?
Asteroids:
- Pieces of rock of various sizes
- Mostly orbit the Sun between Mars and Jupiter (the asteroid belt)
- Have a density similar to the four inner planets
- If asteroids enter the Earth’s atmosphere, they will burn up and fall to Earth as meteors.
- Larger asteroids are classified as dwarf planets.
- Asteroids are classified as minor planets, which are defined as any object that orbits a star that does not have a large enough mass for gravitational attraction.
- Famous asteroid: Ceres
What are comets,what are their characteristics, what is a famous example, and how do they behave when near the Sun?
Comets:
* Consist of dust embedded in ice made from water and methane.
* Have a density similar to the four outer planets.
* They orbit the Sun in highly elliptical orbits. Their distance from the Sun varies significantly.
* When comets approach the Sun, the dust and gas are blown backwards by radiation from the Sun, and the comet shows a bright head and a long tail pointing away from the Sun.
* Famous comet: Halley’s Comet
How do planets, dwarf planets, and comets orbit the Sun, and is the Sun at the center?
- Planets, dwarf planets, and comets orbit the Sun in ellipses.
- The Sun is not at the center of the ellipse.
- For approximating the circular paths of planets, the point can be taken as the center of the ellipse.
How do we use the orbital speed formula for other planets in the Solar System?
The same formula 𝑣 = 2𝜋𝑟 / 𝑇 can be used for any planet (including the Earth) to calculate average orbital speed
Where:
* 𝑟 is the average orbital radius and
* 𝑇 is the orbital period
How much of the Solar System’s mass is in the Sun, and how does this affect gravitational fields?
More than 99% of the mass of the Solar System is concentrated in the Sun. Because of this, the Sun has a much stronger surface gravitational field than the planets, and its gravitational attraction keeps all the objects in orbit.
According to the theory of origin, how did the Sun form?
The Sun is thought to have formed when gravitational attraction pulled together swirling clouds of hydrogen and dust called nebulae in a region of space where their density was high.
How did the planets form after the Sun?
- The planets are created from discs of matter that remain from the nebula that formed the Sun.
- As this material rotated around the Sun, gravitational attraction between small particles caused them to join together and grow in size in an accretion process.
- The evidence for this accretion model of the formation of the Solar System is the approximate age of the Earth being the same as the age of the Moon and the Solar System.
- Also, all planets orbit the Sun in the same plane and rotate in the same direction.
Where did the heavier chemical elements in the Sun and inner planets come from?
They might have come from an exploding supernova.
During the lifetime of a star, atoms of hydrogen and other light elements are fused into atoms of heavier elements.
Why are the inner planets different from the outer planets?
- As the Sun grew, it became hotter.
- In the region of space where inner planets were forming, the temperature would be high for light elements to form heavier elements.
- The inner planets are built of materials with high melting temperatures, such as metals and silicates.
- Further away from the Sun, in cooler regions, light molecules could exist in a solid icy form. The outer planets could grow large enough to capture the light elements.
- The outer planets are large, gaseous, and cold; together their mass is about 99% of the mass orbiting the Sun.
- More than 99% of the mass of the Solar System is concentrated in the Sun.
What factors affect the gravitational field strength of a planet?
The gravitational field strength of a planet increases when:
1. The mass of the planet increases.
2. The distance between the planet and the object decreases (the attraction force is inversely proportional to the square of the distance).
How does a planet’s year, orbital speed, and surface temperature vary with distance from the Sun?
- The planet’s year (time to orbit the Sun) increases with increasing distance from the Sun.
- The orbital speed decreases with increasing distance from the Sun.
- The surface temperature of the planet decreases as distance from the Sun increases.
What force keeps planets in orbit, and how does distance affect orbital speed?
- For planets orbiting the Sun in near-circular paths, the force of gravity between the Sun and the planet provides the necessary centripetal force.
- The strength of the Sun’s gravitational field decreases as the distance between the Sun and the planet increases, so the centripetal force will decrease. This results in a lower orbital speed and longer orbital duration.
How does the speed of a comet change as it orbits the Sun in a large ellipse?
- For a comet with a large elliptical path, its speed increases as it approaches the Sun and decreases as it moves away from the Sun.
- As the comet approaches the Sun, its kinetic energy increases.
- When it moves away, some of the kinetic energy is converted into potential energy.
What is the Sun made of, and what type of star is it?
- The Sun is a medium-sized star which consists mainly of hydrogen and helium.
- The radiant energy it emits is mostly in the infrared, visible, and ultraviolet regions of the electromagnetic spectrum.
- This radiation is emitted from glowing hydrogen, which is heated by energy released in nuclear fusion within the Sun.
How do nuclear reactions power stars like our Sun?
Nuclear Reactions in Stars:
* Stable stars such as our Sun are hot and dense enough for nuclear fusion of hydrogen into helium to occur, releasing large amounts of energy.
* The Sun is powered by a nuclear fusion process in its core.
* Some of the energy generated in the core transfers to the surface of the star. These surface layers are cooler and less dense, but they are hot and contain hydrogen gas that glows and emits electromagnetic radiation into space.
Why do stars vary in size, mass, surface temperature, color, and brightness?
Stars vary in size, mass, surface temperature, color, and brightness. Color and brightness both depend on the surface temperature, which increases with the mass of the star. A white or blue star is hotter than a red or yellow star.
What is a light-year, and why is it used?
- Stars are seen at night and appear close, but the distance between stars is very great.
- A new unit is used to measure these distances, which is the light-year.
- A light-year is the distance traveled in space or vacuum by light in one year.
- 1 light-year = 9.5×10^12 km = 9.5×10^15 m.
How does a protostar form, and what happens as it gains mass?
- When interstellar clouds of dust and gas containing hydrogen collapse under the force of gravitational attraction, a protostar is formed.
- As the mass of the protostar increases, its core temperature increases. When the core becomes hot enough, nuclear fusion can start.
- If the young star has a large mass, it forms a blue or white star. If it has a smaller mass such as our Sun, it forms a red or yellow star.
What is a stable star, and how long does this stage last for a star like the Sun?
- In a stable star (as in the Sun), the very strong forces of gravity pulling inwards are balanced by the opposing forces trying to make it expand due to extremely high temperatures.
- When forces are balanced, the star is in a stable state (for 10,000 million years). During this time, most of the hydrogen in the core is converted into helium.
(Refer to the Star Life Cycle diagram for a visual overview.)
What happens when a star starts to run out of hydrogen?
- It becomes unstable due to less energy being produced by nuclear fusion in the core.
- The core collapses inward under its gravitational force of attraction.
- Potential energy is converted into kinetic energy that makes the core hotter. A fast burn of remaining hydrogen takes place, and a large expansion occurs.
- The expansion and cooling of the surface gases makes the star turn into a red giant (most stars) or red supergiant if the star is massive.
- As the temperature of the core increases again, fusion of helium into carbon occurs.
(Refer to the Star Life Cycle diagram for a visual overview.)
How do low-mass stars end their life cycle?
- When all the helium is used up, the core collapses and becomes a white dwarf at the center of a glowing shell of ionized gas known as a planetary nebula.
- The white dwarf cools into a cold black dwarf containing carbon.
(Refer to the Star Life Cycle diagram for a visual overview.)
How do high-mass stars evolve, and what leads to a supernova?
- Massive stars burn up hydrogen more quickly than low-mass stars, so their stable stage is shorter.
- The core collapses into a supergiant, and nuclear fusion of helium to carbon occurs.
- When all helium has been used up, the core collapses further due to gravitational forces, and its temperature increases and becomes hot enough for the nuclear fusion of carbon into oxygen, nitrogen, and finally iron to occur.
- Nuclear fusion stops, and the energy of the star is released in a supernova explosion.
- In the explosion, there is a large increase in the star’s brightness, and the temperature becomes high enough for fusion of nuclei into heavier elements than iron. These heavy elements are thrown into space as nebula and become ready to form new stars and planetary systems.
(Refer to the Star Life Cycle diagram for a visual overview.)
What remains after a supernova, and under what conditions do neutron stars and black holes form?
- The center of the supernova collapses to a very dense neutron star, which spins rapidly and acts as a pulsar, sending out pulses of radio waves.
- If the red giant is very massive, a black hole is formed. In a black hole, the matter is packed so densely (the mass of Earth would occupy the volume of 1 cm³) that nothing can escape from its gravity, not even light. Intense X-ray radiation may be emitted, which alerts us to its presence.
(Refer to the Star Life Cycle diagram for a visual overview.)
What is a galaxy, and which galaxy does our Solar System belong to?
- A galaxy is a large collection of stars; there are billions of stars in a galaxy.
- The Milky Way is a spiral galaxy to which our Solar System belongs.
- Galaxies can be seen on dark nights as a narrow band of light spreading across the sky.
- Galaxies vary in size and number of stars. They travel in groups. The nearest spiral galaxy in our local cluster is the Andromeda Galaxy.
How large is the Milky Way Galaxy in light-years?
The Milky Way has a diameter of about 100,000 light-years.
How do we know the Universe is expanding, and what is redshift?
- The Universe is made of millions of galaxies.
- When light emitted from stars in distant galaxies is shifted to the red end of the electromagnetic spectrum, it is called redshift (the wavelength of light increases).
- The greater the redshift, the farther away the galaxy is from us. This is explained by the Doppler effect.
- If the source of light approaches us, the waves are crowded into a smaller space, and their wavelength decreases (blueshift). If the source moves away, the wavelength increases (redshift).
- From the size of the redshift of starlight, the speed of recession of the galaxy can be calculated, providing evidence that the Universe is expanding.
What is the Big Bang Theory, and what does it propose?
- If the galaxies are receding from each other, it follows that in the past they were closer together. Therefore, the matter of the Universe was packed together in an extremely dense state.
- The Big Bang theory proposes that this happened from one place with a huge explosion (Big Bang).
- Scientists cannot predict what will happen in the future because the density of the Universe is difficult to calculate. This is partly because 80% of the Universe is made of invisible materials that do not emit radiation.
- The gravitational force between masses is used to determine the motion and evolution of planets, stars, and galaxies, and it controls the fate of the Universe.
What is the cosmic microwave background radiation (CMBR), and why is it important?
Microwave Background Radiation:
- The Big Bang produced radiation energy in the form of cosmic microwave background radiation (CMBR) of a specific frequency. It fills the whole Universe with the same intensity in all directions.
- The CMBR was produced shortly after the Universe was formed.
- Since the Universe is still expanding, this results in a redshift of the cosmic background radiation into the microwave region of the electromagnetic spectrum.
How do we estimate the age of the Universe using Hubble’s Law?
Age of the Universe:
- It is found that the speed of recession (𝑣) of a galaxy is directly proportional to its distance away (𝑑). This is called Hubble’s Law:
- 𝑣 = 𝐻0 × 𝑑
- 𝐻0 (Hubble’s Constant) is defined as the ratio of the speed at which the galaxy is moving away from Earth to its distance from Earth.
- Hubble’s constant represents the rate at which the Universe is expanding at present. Its value is found by measuring the speed of recession of large galaxies whose distances are known.
- Redshifts are used to find the speed of recession, and distance can be calculated from the brightness. The apparent brightness decreases as the inverse square of the distance from the supernova.
- The estimated value of 𝐻0 is 2.2×10^−18 per second.
- The age of the Universe is equal to:
- 1 / 𝐻0 =1 / 2.2×10^−18 = 4.5 × 10^17 s.
