Universe and Solar System – Lecture Review
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These flashcards cover key concepts from the lecture on the Universe and Solar System, including the Big Bang Theory, galaxies, stars, the Sun, planets, moons, small Solar-System bodies, and astronomical units of measurement.
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What does the Big Bang Theory describe?
The universe began 13.8 billion years ago as an extremely hot, dense point that expanded and cooled to form all cosmic matter and space.
Who propounded the Big Bang Theory and in which year?
Georges Lemaître in 1927.
Approximately how old is the universe according to current estimates?
About 13.8 billion years.
What is meant by “cosmic expansion”?
The observation that the universe is still expanding outward from its initial Big Bang origin.
What is a galaxy?
A huge collection of gas, dust, billions of stars, and their solar systems bound together by gravity.
Who coined the term “galaxies”?
Galileo.
Name the three main shapes of galaxies.
Spiral, Elliptical, and Irregular.
What is the name of our home galaxy?
The Milky Way (Akash Ganga), a spiral galaxy.
Which irregular galaxy is the nearest to the Milky Way?
Canis Major Dwarf Galaxy.
Which spiral galaxy is the nearest to the Milky Way?
Andromeda Galaxy.
Of what are stars primarily composed?
Extremely hot hydrogen and helium gases.
Which nuclear process powers stars?
Nuclear fusion.
What is the closest star to Earth?
The Sun.
What is the closest star to the solar system after the Sun?
Proxima Centauri (4.2 light-years away).
What is a supernova?
An exploding star that blasts part of its mass into space.
Will the Sun ever become a black hole?
No; it is not massive enough to form a black hole.
Approximately what fraction of the solar system’s mass is in the Sun?
About 99.86 %.
How far is the Earth from the Sun on average?
About 150 million km (1 Astronomical Unit).
How long does sunlight take to reach Earth?
About 8 minutes 20 seconds.
What is the Sun’s primary chemical composition?
≈ 71 % hydrogen and 26 % helium.
What is the Sun’s approximate rotation period at its equator?
About 25 days.
Define a light-year (ly).
The distance light travels in vacuum in one year (≈ 9.461 × 10¹⁵ m).
Define an Astronomical Unit (AU).
The average Earth–Sun distance (≈ 1.495 × 10¹¹ m).
List the eight planets in order from the Sun.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Which is the hottest planet and why?
Venus, because its thick CO₂ atmosphere traps heat (run-away greenhouse effect).
Why is Venus called Earth’s twin?
Its size and shape are very similar to Earth’s.
Which planet is known as the Red Planet and what gives it that color?
Mars; iron-oxide dust on its surface gives it a reddish cast.
On which planet is Olympus Mons, the tallest mountain and volcano in the solar system?
Mars.
Which is the largest planet in the solar system?
Jupiter.
Name the four Galilean moons of Jupiter.
Io, Europa, Ganymede, and Callisto.
Which two planets are known as the ice giants?
Uranus and Neptune.
Which planet’s 98° axial tilt makes it the “lopsided planet”?
Uranus.
Which planets rotate clockwise (retrograde) relative to most others?
Venus and Uranus.
Which planet has the most prominent ring system, discovered by Galileo?
Saturn.
What is notable about Saturn’s moon Titan?
It is the second-largest moon in the solar system.
Which is the farthest known planet from the Sun?
Neptune.
Which is the smallest planet in the solar system?
Mercury.
Why do Mercury’s days scorch and nights freeze?
It has virtually no atmosphere to regulate temperature.
How long is a Mercurian year (revolution period)?
About 88 Earth days.
State Venus’s rotation and revolution periods.
Rotation ≈ 243 Earth days (retrograde); revolution ≈ 225 Earth days.
State Earth’s rotation and revolution periods.
Rotation ≈ 23 h 56 m 4 s; revolution ≈ 365 days 5 h 45.5 s.
How long is a Martian day (sol)?
≈ 24 h 37 m 23 s.
What is Jupiter’s approximate rotation period?
≈ 9 h 56 m (fastest of all planets).
How long does Saturn take to orbit the Sun?
≈ 29 Earth years.
What is Uranus’s orbital period?
≈ 84 Earth years.
What is Neptune’s orbital period?
≈ 165 Earth years.
What is the average distance between Earth and Moon called apogee and perigee?
Apogee ≈ 406 000 km; perigee ≈ 364 000 km.
How long is a synodic month (lunar phase cycle)?
≈ 29.53 days.
What percentage of the Moon’s surface is visible from Earth?
About 59 %.
Does the Moon have an atmosphere?
No; it is airless, so there is no twilight or sound transmission.
What is the scientific study of the Moon called?
Selenology.
Where is the main asteroid belt located?
Between the orbits of Mars and Jupiter.
What are meteoroids?
Small pieces of rock orbiting the Sun; they become meteors when they enter Earth’s atmosphere.
What happens when a meteoroid survives passage through the atmosphere and lands on Earth?
It is called a meteorite and may create a crater.
Of what are comets composed?
Dust, rock, and ice—frozen leftovers from solar-system formation.
Where are many comets found?
The Kuiper Belt beyond Neptune, following highly elliptical orbits.
How often does Halley’s Comet appear?
Every 75–76 years.
How does the Kuiper Belt compare with the asteroid belt?
It is roughly 20 times wider and 20–100 times more massive.
Name the main layers of the Sun from center outward.
Core, Radiation Zone, Convection Zone, Photosphere, Chromosphere, Corona.