Comprehensive Astronomy: Solar System, Stars, Galaxies, and Cosmology

What is the nebular hypothesis?

The theory that planets formed by the gradual accretion of smaller objects through collisions and gravitational attraction.

What is the frost line?

The distance from the Sun where the solar nebula was cool enough for hydrogen compounds to solidify.

Why did outer planets grow larger than inner planets?

Outer planets condensed from hydrogen compounds as well as rock and metal, while inner planets only formed from rock and metal.

What geological features indicate the activity of a planet's surface?

Cratering, volcanoes, tectonics, and erosion.

What are the three main layers of Earth's interior?

Core, mantle, and crust.

What conditions are necessary for a planet to have a magnetic field?

Rapid rotation, a molten interior, and convection currents.

What characterizes the surface of Mercury?

Heavily cratered with some lava flows and evidence of crust shrinking.

What evidence suggests that Mars was wetter in the past?

Presence of impact craters and volcanoes, indicating a different climate.

What is the primary composition of Venus's atmosphere?

Principally carbon dioxide with a small amount of nitrogen.

What is unique about Jupiter's moon Io?

It is heated by tidal forces, leading to active volcanoes and extensive resurfacing.

What is the primary composition of Saturn's rings?

Composed of water ice particles with a complex structure including ringlets and gaps.

What distinguishes Triton, Neptune's moon?

It is the smallest of the large moons in the solar system, has an atmosphere of nitrogen, and orbits retrograde.

What defines a dwarf planet?

An object that orbits the Sun, is spherical due to gravity, but has not cleared its orbit of other objects.

What are the two main sources of comets?

The Kuiper Belt and the Oort Cloud.

What is the structure of a comet?

Consists of a nucleus (the 'dirty snowball'), a coma, and two tails (plasma and dust) that point away from the Sun.

What methods are used to detect extrasolar planets?

Radial velocity and transit methods, among others.

What is the core structure of the Sun?

Core, radiation zone, convection zone, photosphere, chromosphere, corona, and solar wind.

What is the energy source of the Sun?

The fusion of hydrogen into helium at temperatures above 10,000,000 Kelvin.

What are solar flares?

Sudden eruptions of energy on the Sun's surface.

How is luminosity of stars determined?

By measuring distance (parallax) and apparent brightness, then applying the inverse square law.

What is the Hertzsprung-Russell Diagram used for?

To plot luminosity versus temperature of stars.

What is the main sequence in stellar evolution?

The stable hydrogen fusion stage of stars, like the Sun.

What characterizes high mass stars in the main sequence?

They burn fuel more rapidly and have shorter lifetimes compared to low mass stars.

What are the two classifications of meteorites?

Primitive (unchanged since formation) and processed (once part of a larger differentiated object).

What is the significance of the solar wind?

It streams out from the corona and is shielded from most of it by Earth's magnetic field.

What is the primary composition of Mars's atmosphere?

Principally carbon dioxide with some nitrogen, and very low pressure.

What is the role of the solar neutrinos?

They are evidence of the fusion reactions occurring in the Sun's core.

What are the two main components of the interstellar medium from which stars form?

Gas and dust

What evidence indicates where stars are born in the interstellar medium?

Emission nebulae, 21 cm line, and giant molecular clouds

What happens when gravity becomes stronger than internal pressure in a dense cloud?

The cloud begins to collapse and fragment.

What is the outcome when nuclear fusion of hydrogen begins in a protostar?

Pressure balances gravity, and the star stabilizes.

What type of star forms from a mass below 0.08 solar masses?

A brown dwarf

What occurs to stars with more than 150 solar masses?

Intense radiation drives their outer layers into space.

What is the fate of very low mass stars (0.08 - 0.4 solar masses) after hydrogen is converted to helium?

They gradually cool and become fainter.

What is the process that occurs in low mass stars after hydrogen in the core is exhausted?

Helium shell fusion starts, leading to expansion into a red giant.

What happens to the core of high mass stars (more than 8 solar masses) when it becomes iron?

It collapses into a ball of neutrons, leading to a type II supernova.

What is a nova?

A star that becomes bright due to hydrogen fusion on the surface of a white dwarf.

What is the upper limit for the mass of a neutron star?

2 - 3 solar masses

What forms when a type II supernova occurs in a high mass star of more than 25 solar masses?

A black hole

What is the event horizon of a black hole?

The boundary where escape velocity equals the speed of light.

What type of galaxy is the Milky Way classified as?

A barred spiral galaxy.

What did Hubble discover about galaxies?

There are other galaxies outside the Milky Way.

What is the Hubble Law?

The relationship between distance and speed of recession of galaxies.

What is an Active Galactic Nucleus (AGN)?

A highly luminous active galaxy with features like a bright nucleus and strong emission lines.

What is the Big Bang?

The event that marked the beginning of the universe, expanding from a hot, dense state.

What is the current estimated age of the universe?

About 13.7 billion years.

What does the Drake Equation estimate?

The number of civilizations in our galaxy with which we might be able to communicate.

What is the Fermi Paradox?

The apparent contradiction between the high probability of extraterrestrial life and the lack of contact with such civilizations.

What is the fate of the universe if there is enough matter to cause contraction?

The universe will be bent into a spherical shape, resulting in a closed universe.

What indicates that the universe is flat?

Current observations show that it will expand forever.

What are the conditions for life as we know it?

Carbon-based life forms with water as the liquid medium.

Where is the solar system located in the Milky Way?

In an arm about 25 light years from the center.

What is the significance of dark matter in the Milky Way?

It constitutes a large percentage of the galaxy's total mass.

What happens to galaxies that collide?

They usually create a giant elliptical galaxy.

What is the main energy source for active galaxies?

A supermassive black hole with matter spiraling in.