The Universe includes space-time and everything in it, including matter, energy, galaxies, stars, and planets.
What does the Big Bang model describe?
A Earth’s formation
B A supernova
C The early Universe expanding from a hot, dense state
D The Milky Way’s orbit
The Big Bang model describes how the Universe expanded from an extremely hot, dense early state; it was not an explosion inside empty space.
About how old is the Universe?
A 13.8 billion years
B 4.6 billion years
C 1 million years
D 100 billion years
Measurements of the cosmic microwave background and cosmic expansion place the Universe’s age at about 13.8 billion years.
What is the cosmic microwave background (CMB)?
A A type of star
B A distant galaxy
C A black hole
D Afterglow radiation from the early Universe
The CMB is ancient radiation from the early Universe, released when it cooled enough for light to travel freely.
Which observation supports the expansion of the Universe?
A Earth’s seasons
B The Moon’s phases
C Redshift of distant galaxies
D Sunspots
As space expands, light from distant galaxies is stretched toward longer wavelengths. This cosmological redshift is evidence that the Universe is expanding.
What does the observable Universe mean?
A The whole Universe
B The region whose light has had time to reach us
C Only the Milky Way
D Every star visible to the naked eye
The observable Universe is the region from which light has had time to reach us since the Universe began.
Which galaxy contains Earth and the Solar System?
A Andromeda
B Orion
C Milky Way
D Sombrero
Earth and the Solar System are within the Milky Way, our home galaxy.
How is the Milky Way classified?
A Elliptical galaxy
B Irregular galaxy
C Ring galaxy
D Barred spiral galaxy
The Milky Way is classified as a barred spiral galaxy, with a central bar and spiral arms.
What kind of object is the Sun?
A A star
B A planet
C A galaxy
D A moon
The Sun is a star: a hot ball of gas that produces energy through nuclear fusion in its core.
Which star is nearest to the Sun besides the Sun itself?
A Sirius
B Proxima Centauri
C Betelgeuse
D Vega
Proxima Centauri, a red dwarf in the Alpha Centauri system, is the closest star to the Sun after the Sun.
What does a light-year measure?
A Time
B Brightness
C Temperature
D Distance
A light-year measures distance: how far light travels in one year, about 9.46 trillion kilometers.
One astronomical unit (AU) is approximately what distance?
A 150 million km
B 1.5 million km
C 150,000 km
D 1.5 billion km
One astronomical unit is about the average Earth–Sun distance, roughly 150 million kilometers.
Which is the nearest large galaxy to the Milky Way?
A Triangulum
B Whirlpool
C Andromeda
D Sombrero
Andromeda is the nearest large galaxy to the Milky Way and a major member of our Local Group.
What is a nebula?
A A cloud of gas and dust
B A type of galaxy
C An asteroid
D A planet
A nebula is a large cloud of interstellar gas and dust. Some nebulae are places where stars form.
Where do many stars begin to form?
A Asteroid belts
B Dense molecular clouds
C Black holes
D Globular clusters
Stars form in dense regions of molecular clouds as gravity pulls gas and dust together.
What is the Sun’s main source of energy?
A Chemical burning
B Fission only
C Nuclear fusion
D Friction
The Sun releases energy mainly through nuclear fusion, combining hydrogen nuclei into helium in its core.
Which element is most abundant in the Universe?
A Hydrogen
B Oxygen
C Carbon
D Iron
Hydrogen is by far the most abundant element in the Universe.
Which force helps hold stars and gas together in galaxies?
A Sound waves
B Electricity
C Magnetism alone
D Gravity
Gravity holds stars, gas, dust, and other matter together in galaxies.
What is the approximate present-day temperature of the CMB?
A About 2.7 K
B About 27 K
C About 270 K
D About 0.27 K
The cosmic microwave background has an average temperature close to 2.7 kelvin today.
As the Universe expands, cosmological redshift moves light toward what?
A Shorter wavelengths
B Longer wavelengths
C No wavelength change
D Radio waves only
Cosmic expansion stretches light traveling through space, increasing its wavelength toward the red end of the spectrum.
What is the event horizon of a black hole?
A The boundary beyond which light cannot escape
B Its visible surface
C The center of a galaxy
D The edge of a nebula
The event horizon marks the boundary around a black hole beyond which light cannot escape.
How do scientists infer the presence of dark matter?
A By its visible glow
B By sound waves
C By its heat alone
D By its gravitational effects
Dark matter does not emit visible light, but scientists infer its presence from its gravitational effects on matter and light.
Dark energy is associated with which large-scale effect?
A Planet formation
B Solar flares
C Accelerated expansion of the Universe
D Earth’s rotation
Dark energy is the name for the unknown component associated with the accelerating expansion of the Universe.
What is an exoplanet?
A A moon outside a galaxy
B A planet orbiting a star other than the Sun
C A star without planets
D A distant comet
An exoplanet is a planet orbiting a star other than our Sun.
What can remain after a Sun-like star sheds its outer layers?
A A neutron star
B A black hole
C A white dwarf
D A protostar
When a Sun-like star sheds its outer layers, its remaining core becomes a white dwarf.
What is one possible remnant of a massive star after a supernova?
A A planet’s core
B A gas cloud
C A galaxy cluster
D A neutron star
After some massive stars explode as supernovae, their collapsed cores can become neutron stars.
What is a supernova?
A A powerful stellar explosion
B A planet eclipse
C A galaxy’s rotation
D A comet shower
A supernova is a powerful stellar explosion. Different types can occur through different physical processes.
What is gravitational lensing?
A A star changing color
B A planet crossing a star
C Light bending due to gravity
D A galaxy producing sound
Gravity from a massive object can bend the path of light. Astronomers call this effect gravitational lensing.
What is a galaxy cluster?
A A single star
B A large group of galaxies held together by gravity
C A star-forming cloud
D A planetary system
Galaxy clusters are large collections of galaxies held together by gravity.
A parsec is approximately equal to how many light-years?
A About 1 light-year
B About 10 light-years
C About 150 million km
D About 3.26 light-years
A parsec is an astronomical distance unit equal to about 3.26 light-years.