Astronomers form a hypothesis about why a star dims every few days. In the scientific method, what comes next?Wikipedia, "Scientific method". DSST outline area I (5%), b. Applications of scientific thinking
In Karl Popper's sense, a claim counts as scientific only if which of these is true?Wikipedia, "Falsifiability". DSST outline area I (5%), a. Nature and methods of science
In Ptolemy's model of the second century CE, what sat at the center of the universe?Las Cumbres Observatory SpaceBook, "History of Cosmology". DSST outline area I (5%), c. History of early astronomy
Show all 60 questions (57 more)
Astrophysics 9
A comet and a planet both obey Kepler's first law. What does it say about each one's path?Wikipedia, "Kepler's laws of planetary motion". DSST outline area II (15%), a. Kepler's laws and orbits
A planet is at perihelion, its closest point to the Sun. What does Kepler's second law say about its speed there?Wikipedia, "Kepler's laws of planetary motion". DSST outline area II (15%), a. Kepler's laws and orbits
About how fast must an object leave the Earth's surface to escape Earth's gravity without further thrust?Wikipedia, "Escape velocity". DSST outline area II (15%), b. Newtonian physics and gravity
How does general relativity describe gravity?Wikipedia, "General relativity". DSST outline area II (15%), c. Relativity
Kepler's third law ties the square of a planet's period to the cube of its orbit's semi-major axis. In years and astronomical units, what is the period of a body orbiting the Sun at 4 AU?Wikipedia, "Kepler's laws of planetary motion". DSST outline area II (15%), a. Kepler's laws and orbits
Two asteroids drift to twice their original distance apart. By Newton's law of universal gravitation, what happens to the gravitational force between them?Wikipedia, "Newton's law of universal gravitation". DSST outline area II (15%), b. Newtonian physics and gravity
Which observation of Mercury did general relativity explain that Newton's theory could not fully account for?Wikipedia, "General relativity". DSST outline area II (15%), c. Relativity
Which of these is a postulate of special relativity?Wikipedia, "Special relativity". DSST outline area II (15%), c. Relativity
Which statement is Newton's first law of motion?Wikipedia, "Newton's laws of motion". DSST outline area II (15%), b. Newtonian physics and gravity
Celestial systems 6
A sidereal day is one turn of the Earth measured against the stars. About how long is it?Las Cumbres Observatory SpaceBook, "Sidereal Time". DSST outline area III (10%), c. Seasons, calendar and time keeping
About how long does the Moon take to run through one full cycle of phases?Wikipedia, "Lunar phase". DSST outline area III (10%), b. Earth and the Moon
At first-quarter Moon the Sun and the Moon pull on Earth's oceans at right angles. What tides result?Wikipedia, "Tide". DSST outline area III (10%), b. Earth and the Moon
It is summer in Chicago while it is winter in Sydney. What is the reason?Wikipedia, "Season". DSST outline area III (10%), c. Seasons, calendar and time keeping
The Moon's shadow can fall on the Earth during only one lunar phase. Which one?Wikipedia, "Solar eclipse". DSST outline area III (10%), a. Celestial motions
Where is the Moon in its orbit when we see a full moon?Las Cumbres Observatory SpaceBook, "Moon Phases". DSST outline area III (10%), b. Earth and the Moon
The science of light 9
A radio astronomer and an X-ray astronomer compare notes. Which list puts five kinds of light in order from the longest waves to the shortest?Wikipedia, "Electromagnetic spectrum". DSST outline area IV (15%), a. The electromagnetic spectrum
By the Stefan-Boltzmann law, the energy a star radiates from each square meter is proportional to which power of its temperature?Wikipedia, "Stefan-Boltzmann law". DSST outline area IV (15%), d. Blackbody radiation
The spectral lines of a galaxy are shifted toward longer, redder wavelengths. What does that show?Las Cumbres Observatory SpaceBook, "Redshift". DSST outline area IV (15%), c. Spectroscopy
Star A's spectrum peaks in blue light and star B's peaks in red. What does Wien's law say about them?Wikipedia, "Wien's displacement law". DSST outline area IV (15%), d. Blackbody radiation
What do the dark absorption lines in a star's spectrum most directly reveal?Las Cumbres Observatory SpaceBook, "Spectroscopy". DSST outline area IV (15%), c. Spectroscopy
What gathers and focuses the light in a refracting telescope?Wikipedia, "Refracting telescope". DSST outline area IV (15%), b. Telescopes and the measurement of light
Which flaw of lenses do reflecting telescopes avoid?Las Cumbres Observatory SpaceBook, "Reflecting Telescopes". DSST outline area IV (15%), b. Telescopes and the measurement of light
Why are radio telescope dishes built so much larger than optical telescopes?Las Cumbres Observatory SpaceBook, "Radio Telescopes". DSST outline area IV (15%), b. Telescopes and the measurement of light
Why are X-ray and gamma-ray telescopes placed in space?Las Cumbres Observatory SpaceBook, "Space Telescopes". DSST outline area IV (15%), b. Telescopes and the measurement of light
Planetary systems 12
How does the transit method reveal an exoplanet?Las Cumbres Observatory SpaceBook, "Transit Method". DSST outline area V (20%), c. Exoplanets
In the nebular theory, what did the planets form from?NASA Science, "Solar System: Facts". DSST outline area V (20%), b. Formation and evolution of planetary systems
Mercury, Venus, Earth and Mars share which description?NASA Science, "Solar System: Facts". DSST outline area V (20%), a. Contents of our solar system
What defines a star's habitable zone?Las Cumbres Observatory SpaceBook, "What Are the Requirements for Life to Arise and Survive?". DSST outline area V (20%), d. Habitability and life in the Universe
What does the radial velocity method of finding exoplanets measure?Las Cumbres Observatory SpaceBook, "Radial Velocity Method". DSST outline area V (20%), c. Exoplanets
What is Jupiter mostly made of?NASA Science, "Jupiter Facts". DSST outline area V (20%), a. Contents of our solar system
What is the distant Oort Cloud thought to be the source of?NASA Science, "Oort Cloud Facts". DSST outline area V (20%), a. Contents of our solar system
What is the leading explanation for the origin of the Moon?NASA Science, "Moon Formation". DSST outline area V (20%), b. Formation and evolution of planetary systems
Where is the main asteroid belt?Wikipedia, "Asteroid belt". DSST outline area V (20%), a. Contents of our solar system
Why are the planets nearest the Sun small and rocky?Las Cumbres Observatory SpaceBook, "Planets and How They Formed". DSST outline area V (20%), b. Formation and evolution of planetary systems
Why is Venus hotter than Mercury, although Mercury is closer to the Sun?NASA Science, "Venus Facts". DSST outline area V (20%), a. Contents of our solar system
Why was Pluto reclassified as a dwarf planet in 2006?Las Cumbres Observatory SpaceBook, "Dwarf Planets". DSST outline area V (20%), a. Contents of our solar system
The Sun and stars 9
A white dwarf cannot stay stable above a mass of about 1.4 Suns. What is that ceiling called?Wikipedia, "Chandrasekhar limit". DSST outline area VI (15%), c. Birth, life and death of stars
About how long is the Sun's cycle of sunspot activity?NASA Science, "Sun Facts". DSST outline area VI (15%), a. Our Star, the Sun
In the spectral sequence O, B, A, F, G, K, M, which class holds the hottest stars?Las Cumbres Observatory SpaceBook, "Types of Stars". DSST outline area VI (15%), b. Properties and classification of stars
In which region of the Sun is hydrogen fused into helium?NASA Science, "Sun Facts". DSST outline area VI (15%), a. Our Star, the Sun
What can remain where a massive star's core was after a supernova?Las Cumbres Observatory SpaceBook, "Supernova". DSST outline area VI (15%), c. Birth, life and death of stars
What will a star like the Sun leave behind after it sheds its outer layers?Las Cumbres Observatory SpaceBook, "Low Mass Star". DSST outline area VI (15%), c. Birth, life and death of stars
Which of these stars will have the shortest life?Las Cumbres Observatory SpaceBook, "High Mass Star". DSST outline area VI (15%), b. Properties and classification of stars
Which two properties of stars does a Hertzsprung-Russell diagram plot against each other?Wikipedia, "Hertzsprung-Russell diagram". DSST outline area VI (15%), b. Properties and classification of stars
Why does fusion in the core of a massive star stop when the core has turned to iron?Las Cumbres Observatory SpaceBook, "High Mass Star". DSST outline area VI (15%), d. Nuclear fusion and the origin of the elements
Galaxies 6
A star shows a parallax angle of 0.5 arcsecond. How far away is it?Las Cumbres Observatory SpaceBook, "Parallax and Distance Measurement". DSST outline area VII (10%), c. Measuring Cosmic Distances
Edwin Hubble grouped galaxies into spirals, barred spirals, irregulars and which other class?Las Cumbres Observatory SpaceBook, "Galaxy Classification". DSST outline area VII (10%), b. Classification and structure of galaxies
Seen from outside, which shape would our own galaxy show?Wikipedia, "Milky Way". DSST outline area VII (10%), a. Our Galaxy: The Milky Way
What lies at the very center of the Milky Way?Wikipedia, "Milky Way". DSST outline area VII (10%), a. Our Galaxy: The Milky Way
Why are Cepheid variable stars useful for measuring distances to other galaxies?Las Cumbres Observatory SpaceBook, "Cepheid Variable Stars, Supernovae and Distance Measurement". DSST outline area VII (10%), c. Measuring Cosmic Distances
Why can Type Ia supernovae serve as standard candles?Las Cumbres Observatory SpaceBook, "Cepheid Variable Stars, Supernovae and Distance Measurement". DSST outline area VII (10%), c. Measuring Cosmic Distances
The universe 6
Microwaves reach Earth almost evenly from every direction of the sky. Where does this background come from?Las Cumbres Observatory SpaceBook, "The Early Universe". DSST outline area VIII (10%), b. The Big Bang and Hubble's law
The Milky Way sits in a poor cluster of about 50 galaxies. What is that cluster called?Las Cumbres Observatory SpaceBook, "Distribution of Galaxies". DSST outline area VIII (10%), a. Galaxy clusters and large-scale structure
Stars far from the center of a spiral galaxy orbit about as fast as stars closer in. What does this flat rotation curve suggest?Wikipedia, "Galaxy rotation curve". DSST outline area VIII (10%), d. Dark matter and dark energy
What did Edwin Hubble find when he compared the distances of galaxies with their redshifts?Las Cumbres Observatory SpaceBook, "The Universe Now". DSST outline area VIII (10%), b. The Big Bang and Hubble's law
What is dark energy invoked to explain?NASA Science, "Dark Matter and Dark Energy". DSST outline area VIII (10%), d. Dark matter and dark energy
Who discovered the cosmic microwave background in 1965?Wikipedia, "Cosmic microwave background". DSST outline area VIII (10%), b. The Big Bang and Hubble's law
How this list was compiled: Our own questions, written to the exam content outline in the DSST fact sheet for Astronomy (Prometric, Rev 06/2018, https://getcollegecredit.com/wp-content/uploads/2022/09/Astronomy.pdf, read 2026-10-12): Introduction to the Science of Astronomy 5%, Astrophysics 15%, Celestial Systems 10%, The Science of Light 15%, Planetary Systems 20%, The Sun and Stars 15%, Galaxies 10%, The Universe 10%. This bank holds 60: 3, 9, 6, 9, 12, 9, 6 and 6, the same shares. Every fact was read on 2026-10-12 on the public page named under its question: NASA Science, the SpaceBook of Las Cumbres Observatory and Wikipedia. Two answers are arithmetic from a law the source states. Licence: Questions, choices and explanations are original work of this site.
How it works
This Astronomy DSST practice test has 60 questions of our own in the fact sheet's eight areas, in the same shares. It is unofficial and is not affiliated with, endorsed by or sponsored by Prometric, which owns the DSST exams.
Read the full guide
What the exam covers
The fact sheet (Rev 06/2018) lists eight areas: the science of astronomy 5%, astrophysics 15%, celestial systems 10%, the science of light 15%, planetary systems 20%, the Sun and stars 15%, galaxies 10%, and the universe 10%. The bank holds 3, 9, 6, 9, 12, 9, 6 and 6.
The arithmetic
Two questions need a sum: Kepler's third law in years and astronomical units, and distance in parsecs as 1 divided by the parallax in arcseconds. Both are worked in the explanation.
Planetary systems is the largest area at 20%: the planets, how the solar system formed, exoplanets and habitability.
Light is 15%: the order of the spectrum, Wien's law for color and temperature, and Doppler shifts.
Questions and answers
Is there a DSST Astronomy study guide?
The free one is Prometric's fact sheet, with the outline, its percentages and a reference list. On this page each explanation names the NASA, Las Cumbres Observatory or Wikipedia page it was checked on.
How many questions are on the DSST Astronomy exam?
100, to be answered in 2 hours. The fact sheet adds that some of them are unscored pretest questions. Exam mode here draws 50 for 60 minutes.
What score do you need to pass the DSST Astronomy exam?
No percent is published. The American Council on Education recommends 3 semester hours of lower-level credit for a score of at least 400, and the college you send the score to decides what it awards.
Are these real DSST Astronomy questions?
No. All 60 were written for this page from the outline. None is copied or reworded from the exam or from the sample questions in the fact sheet, so a score here says nothing about a score there.