Astronomy Chapters 21–22: Modern Astronomy and Solar System
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74 Terms
Who was the first Greek to calculate Earth's circumference?
Eratosthenes (276 BC - 194 BC)
What view of the universe did most ancient Greeks hold?
A geocentric (Earth-centered) view
What are the seven heavenly bodies in ancient astronomy?
The Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn
Who proposed the heliocentric model of the universe?
Aristarchus (312-230 B.C.)
What is retrograde motion?
The apparent westward drift of planets as Earth overtakes them
What did Ptolemy use to explain retrograde motion?
Large orbital circles called deferents and small circles called epicycles
What significant model did Nicolaus Copernicus create?
A model of the solar system with the Sun at the center
What did Tycho Brahe attempt to observe?
Stellar parallax
What are Johannes Kepler's three laws of planetary motion?
1. Orbits are elliptical, 2. Planets sweep out equal areas in equal times, 3. The square of the orbital period is proportional to the cube of the semi-major axis
What did Galileo Galilei contribute to astronomy?
He constructed an astronomical telescope and made several observations, including the moons of Jupiter and phases of Venus
What is the law of universal gravitation?
It states that every mass attracts every other mass with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.
How many constellations are recognized today?
88 constellations
What are the two locational components of the equatorial system?
Declination and right ascension
What is the difference between a mean solar day and a sidereal day?
A mean solar day is about 24 hours, while a sidereal day takes about 23 hours, 56 minutes, and 4 seconds.
What is perihelion?
The point in Earth's orbit where it is closest to the Sun
What is aphelion?
The point in Earth's orbit where it is farthest from the Sun
What is precession in relation to Earth?
A very slow movement of Earth's axis that completes a cycle every 26,000 years.
What is the synodic month?
The apparent period of the Moon's phases, taking about 29 1/2 days.
What is a lunar eclipse?
An event where the Moon moves within the shadow of Earth, occurring only during the full-Moon phase.
What is a solar eclipse?
An event where the Moon moves directly between Earth and the Sun, occurring only during the new-Moon phase.
Why do eclipses not occur every month?
Because the Moon's orbit is inclined about 5 degrees to the plane of the ecliptic.
What is the plane of the ecliptic?
An imaginary plane that connects Earth's orbit with the celestial sphere.
What is the significance of the celestial sphere in astronomy?
It is a model that represents the apparent positions of stars and celestial objects in the sky.
What did Sir Isaac Newton contribute to astronomy?
He formulated the laws of motion and the law of universal gravitation.
What is the relationship between a planet's orbital period and its distance to the Sun?
It is described by Kepler's third law: p² = d³, where p is the orbital period and d is the distance in astronomical units.
What does the solar system include?
The Sun, eight planets and their satellites, Pluto (now a dwarf planet), asteroids, comets, and meteoroids.
What are the two groups of planets in the solar system?
Terrestrial (inner) planets and Jovian (outer) planets.
Which planets are classified as terrestrial planets?
Mercury, Venus, Earth, and Mars.
What are the characteristics of terrestrial planets?
They are small, dense, rocky, and have low escape velocities.
Which planets are classified as Jovian planets?
Jupiter, Saturn, Uranus, and Neptune.
What are the characteristics of Jovian planets?
They are large, low density, gaseous, massive, and have thick atmospheres.
What is the nebular hypothesis?
It suggests that planets formed about 5 billion years ago from a gaseous nebula.
What is chemical differentiation?
The process where dense metallic elements sink toward a planet's center while lighter elements migrate to the surface.
What is the diameter of Earth's Moon?
3475 kilometers (2150 miles).
What is the gravitational attraction of the Moon compared to Earth?
One-sixth of Earth's gravitational attraction.
What are the two types of terrain on the Moon?
Maria (dark, smooth lowlands) and Highlands (bright, cratered regions).
What are lunar regolith?
Gray, unconsolidated debris covering all lunar terrains, composed of igneous rocks, breccia, glass beads, and fine lunar dust.
What is the significance of the Copernicus crater?
It is an example of a rayed crater, with material ejected from it still visible.
What is the largest planet in the solar system?
Jupiter.
What is the Great Red Spot?
A counterclockwise rotating cyclonic storm located in Jupiter's southern hemisphere.
How many moons does Jupiter have?
At least 63 moons.
What are the Galilean satellites?
The four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto.
What is Saturn known for?
Its prominent rings and dynamic atmosphere.
What is unique about Uranus's rotation?
It rotates 'on its side'.
What is the atmosphere of Venus primarily composed of?
97% carbon dioxide.
What is the surface temperature of Venus?
Approximately 450˚C (900˚F).
What is Olympus Mons?
The largest volcano in the solar system, located on Mars.
What are the polar caps of Mars composed of?
Water ice covered by a thin layer of frozen carbon dioxide.
What are the two moons of Mars?
Phobos and Deimos.
What is the primary component of Jupiter's atmosphere?
Hydrogen and helium.
What is the significance of Titan?
It is Saturn's largest moon and has a substantial atmosphere.
What is the surface pressure on Venus compared to Earth?
90 times that of Earth's.
What is the age of the Moon's original crust?
About 4.5 billion years old.
What is the strongest magnetic field in the solar system associated with?
Neptune
What is the Great Dark Spot on Neptune?
A storm with white cirrus-like clouds above the main cloud deck.
What is the largest moon of Neptune?
Triton
What is unique about Triton's orbit?
It orbits in the opposite direction of Neptune's rotation.
What is the lowest surface temperature recorded in the solar system?
-391ºF on Neptune.
What is the primary composition of Neptune's atmosphere?
Mostly nitrogen with some methane.
What type of volcanic activity is observed on Neptune?
Cryovolcanism.
What defines a dwarf planet?
A celestial body that orbits the Sun and is not the only object in its area of space.
What is Pluto's classification in the solar system?
It is a prototype of dwarf planets.
Where is Pluto located?
In the Kuiper belt.
What is the average temperature on Pluto?
-210ºC.
How long does it take Pluto to orbit the Sun?
248 years.
What are asteroids primarily composed of?
Small bodies, mostly found between Mars and Jupiter.
What is the largest asteroid classified as a dwarf planet?
Ceres.
What are comets often compared to?
Large, 'dirty snowballs.'
What is the most famous short-period comet?
Halley's Comet.
What happens to frozen gases in a comet as it approaches the Sun?
They vaporize, producing a glowing head called the coma.
What are meteoroids called when they enter Earth's atmosphere?
Meteors.
What occurs during a meteor shower?
Earth encounters a swarm of meteoroids associated with a comet's path.
What are the three types of meteorites classified by composition?
Irons, stony, and stony-irons.
What are carbonaceous chondrites believed to be remnants of?
The original solar nebula.