Astronomy Unit Test guide

Flashcards for astronomy exam review.

Asteroid

A rocky object, mostly found in the asteroid belt between Mars and Jupiter.

Comet

A small icy object from the outer solar system with a tail when near the Sun.

Astronomical Unit (AU)

Average distance from Earth to the Sun (~93 million miles or 150 million km).

Revolution

One complete orbit around another body (Earth's revolution = 1 year).

Rotation

One complete spin on an axis (Earth's rotation = 1 day).

Terrestrial Planet

Rocky planets: Mercury, Venus, Earth, and Mars.

Galilean Moon

The four largest moons of Jupiter discovered by Galileo (Io, Europa, Ganymede, Callisto).

Gas Giant

Large planets made mostly of gas: Jupiter, Saturn, Uranus, Neptune.

Dwarf Planet

A body orbiting the Sun, like a planet but not dominant in its orbit (e.g., Pluto).

Spectroscope

Tool that breaks light into a spectrum to analyze composition.

Telescope

Tool to observe distant objects in space by collecting light.

Light-Year

Distance light travels in one year (~6 trillion miles).

Apparent Magnitude

How bright a star appears from Earth.

Absolute Magnitude

The true brightness of a star at a standard distance.

Luminosity

Total energy output of a star per second.

Nuclear Fusion

Process powering stars; hydrogen atoms fuse into helium.

Star

A ball of gas undergoing nuclear fusion.

Radiative Zone

Layer of a star where energy moves outward as radiation.

Convection Zone

Layer where hot plasma rises and cooler plasma sinks.

Photosphere

The visible surface of the Sun.

Chromosphere

A reddish layer above the photosphere.

Corona

The Sun’s outer atmosphere; visible during eclipses.

Hertzsprung-Russell Diagram (H-R Diagram)

Graph showing relationship between star brightness and temperature.

Main Sequence Star

A stable star in the middle of its life (like our Sun).

Nebula

A cloud of gas and dust; birthplace of stars.

White Dwarf

The remains of a low-mass star after it sheds its outer layers.

Supernova

Massive explosion marking the death of a large star.

Neutron Star

Extremely dense remnant of a supernova.

Black Hole

A region of space with gravity so strong not even light can escape.

Galaxy

A massive system of stars, gas, dust, and dark matter.

Dark Matter

Invisible matter that affects gravity but doesn’t emit light.

Parallax

Apparent shift in position of a nearby star due to Earth's orbit; used to measure distance.

Inner planets (Mercury, Venus, Earth, Mars)

Small, rocky, solid surfaces, closer to the Sun, fewer moons, no rings.

Outer planets (Jupiter, Saturn, Uranus, Neptune)

Large, made of gas or ice, have rings and many moons, far from the Sun.

Inside the solar system

Use Astronomical Units (AU).

Outside the solar system

Use Light-years (ly) and parsecs.

Why isn’t Pluto a planet anymore?

Pluto was reclassified as a dwarf planet because it hasn’t cleared its orbital path.

Difference between a moon and a dwarf planet?

A moon orbits a planet; a dwarf planet orbits the Sun but doesn’t dominate its orbit.

Asteroids

Asteroids are rocky and mostly in the asteroid belt.

Comets

Comets are icy and from the outer solar system; they form tails when near the Sun.

How is the night sky mapped?

Using constellations as reference patterns. Modern sky maps divide the sky into 88 official constellations.

Telescopes

Telescopes collect light to see distant objects more clearly.

Spectroscopes

Spectroscopes analyze light to learn what stars and galaxies are made of and how they move.

How does a star progress through its life?

Nebula → gas/dust cloud, Main sequence → stable, fusion-powered, Red giant or supergiant, Ends as White dwarf (small star) or Supernova → Neutron star or black hole (massive star)

How do you use a H-R Diagram?

It compares temperature (x-axis) and luminosity/brightness (y-axis) of stars. Helps identify a star’s type and stage of life (main sequence, giant, dwarf).

Spiral Galaxy

Like the Milky Way; has arms and a central bulge.

Elliptical Galaxy

Round or oval, older stars, little gas/dust.

Irregular Galaxy

No clear shape, often caused by galaxy collisions.