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Twenty representative DSST Astronomy questions, each with the answer and a short explanation of why the wrong choices trap test-takers.
By Alex Stone6 min readLast fact-checked January 1970
Twenty practice questions for DSST Astronomy, in the real exam's style. Score 16 of 20 here and you are in passing range. Miss more than four, and the pattern of your misses points straight at the topic to review next. Every question below is explained on video, including why the wrong answers trap most test-takers.
What students preparing for this exam tell us is that steady practice in the exam's format, with an explanation for every miss, is what moves a score. Use these the same way: answer, check, and read why the wrong choices are tempting. For the full plan around them, see the DSST Astronomy pillar guide.
Watch the full video walkthrough above, then test yourself on the twenty questions below. Each one is explained on the video, including why the wrong answers trap most test-takers.
1. The apparent daily rising and setting of the Sun, Moon, and stars is caused mainly by: The Earth Rotating on Its Axis. The whole sky appears to wheel from east to west once a day because the Earth spins on its axis from west to east. The objects are nearly fixed; it is the ground beneath us that is turning.
2. The seasons on Earth are caused primarily by: The Tilt of Earth's Axis. Earth's axis is tilted about twenty-three and a half degrees, so as it orbits, each hemisphere leans toward the Sun for part of the year and away for the rest. That changing angle of sunlight, not our distance from the Sun, drives the seasons.
3. A light-year is a unit of: Distance. Despite the word year, a light-year measures distance, the distance light travels in one year, about six trillion miles. It is used because the distances between stars are far too large for ordinary units.
4. Which of the following lists the correct order of these layers of the Sun from the inside out? Core, Photosphere, Corona. The Sun's energy is produced in the core at the center. It then works outward to the photosphere, the visible surface, and finally to the corona, the faint outer atmosphere seen during a total eclipse.
5. The energy radiated by the Sun is produced by: Nuclear Fusion of Hydrogen Into Helium. Deep in the Sun's core, immense pressure and heat fuse hydrogen nuclei into helium, releasing enormous energy. This nuclear fusion, not ordinary burning, is what powers the Sun and all main-sequence stars.
6. The phases of the Moon are caused by: The Changing Amounts of the Sunlit Side We See as the Moon Orbits Earth. Half the Moon is always lit by the Sun. As the Moon orbits Earth, we see different fractions of that sunlit half, which gives us the cycle from new moon to full moon. The Earth's shadow is not involved.
7. A solar or lunar eclipse does NOT happen every month because: The Moon's Orbit Is Tilted Relative to Earth's Orbit. The Moon's orbit is tilted about five degrees to the plane of Earth's orbit, so usually the Moon passes above or below the perfect line-up. Only when the three bodies align closely enough does an eclipse occur.
8. Which group lists only terrestrial (rocky) planets? Mercury, Venus, Earth, Mars. The four inner planets, Mercury, Venus, Earth, and Mars, are small, dense, and rocky. The outer giants like Jupiter and Saturn are large and made mostly of gas and liquid, so they are not terrestrial planets.
9. The tides on Earth are caused mainly by: The Gravitational Pull of the Moon, and to a Lesser Extent the Sun. Tides arise because the Moon's gravity pulls harder on the near side of Earth than the far side, stretching the oceans into bulges. The Sun adds a smaller effect, strongest when Sun, Earth, and Moon line up.
10. According to Kepler's laws, the orbit of a planet around the Sun is: An Ellipse with the Sun at One Focus. Kepler showed that planets travel on ellipses, slightly flattened circles, with the Sun sitting at one focus rather than at the center. This replaced the old belief that orbits had to be perfect circles.
11. What property of a star does its color tell you most directly? Its Surface Temperature. A star's color reveals its surface temperature: blue stars are the hottest, while red stars are the coolest. Our yellow-white Sun sits in the middle of that range.
12. On the Hertzsprung-Russell diagram, the diagonal band where most stars, including the Sun, spend most of their lives is called the: The Main Sequence. The main sequence is the long diagonal band on the Hertzsprung-Russell diagram where stars fuse hydrogen in their cores. Stars like the Sun spend about ninety percent of their lives there.
13. A typical low-mass star like the Sun will end its life as a: A White Dwarf. After swelling into a red giant and shedding its outer layers, a Sun-like star leaves behind a hot, dense core called a white dwarf. Only much more massive stars end as neutron stars or black holes.
14. A supernova is: The Explosive Death of a Massive Star. A supernova is the violent explosion that ends the life of a massive star, briefly outshining an entire galaxy. It scatters newly forged heavy elements into space, seeding future stars and planets.
15. Stars are born in: Clouds of Gas and Dust Called Nebulae. Stars form inside cold, dense clouds of gas and dust called nebulae. Gravity pulls a clump together until its center grows hot enough for nuclear fusion to ignite, and a new star switches on.
16. The galaxy that contains our solar system is called the: The Milky Way. Our Sun is one of a few hundred billion stars in the Milky Way, a spiral galaxy. The faint band of light we call the Milky Way in the night sky is our view edge-on into its disk.
17. The most common evidence that the universe is expanding is that distant galaxies show a: Redshift in Their Light. Light from distant galaxies is shifted toward longer, redder wavelengths, a redshift. The farther away a galaxy is, the greater its redshift, which tells us those galaxies are moving away as the universe expands.
18. The theory that the universe began in an extremely hot, dense state and has been expanding ever since is called: The Big Bang Theory. The Big Bang theory holds that the universe began about fourteen billion years ago from an extremely hot, dense state and has been expanding ever since. The cosmic microwave background is its leftover glow.
19. The faint glow of microwave radiation coming from all directions in the sky, considered strong evidence for the Big Bang, is the: The Cosmic Microwave Background. The cosmic microwave background is leftover heat from the early universe, now cooled to just a few degrees above absolute zero. Finding it in every direction confirmed a key prediction of the Big Bang.
20. Our solar system is located: In One of the Milky Way's Spiral Arms, Far From the Center. The Sun sits in a spiral arm of the Milky Way, roughly halfway out from the galaxy's crowded center, about twenty-six thousand light-years away. We are in a fairly ordinary neighborhood of an ordinary spiral galaxy, not at its core.
The point of twenty questions is not the twenty, it is the pattern. Mark which topic each miss came from, then spend your next session on that topic alone. None of it requires starting over, only tightening the spots that cost you points.
A single twenty-question set is a snapshot, not a study plan. To pass with margin you need volume: enough questions, in the exam's format, with explanations that turn a wrong answer into a correction. That is what Flying Prep's DSST Astronomy practice is built for: every question explained, with a free trial before you decide.
About 16. A passing score works out to roughly 80 percent, so clearing 16 of 20 consistently across a few sets puts you in passing range.
No. These are representative practice questions in the exam's style. The real exam draws from a much larger pool, which is why practice volume, not memorizing any single set, is what moves your score.
The Flying Prep DSST Astronomy question bank has every question explained and reviewed against the current outline. Start a free trial and drill the topics your misses point to.
Alex Stone founded Flying Prep after earning her bachelor's degree from Thomas Edison State University using 27 CLEP and DSST exams to test out of 99 credits. She built Flying Prep to help working adults and returning students take the same path.
See the full DSST Astronomy study guide for the practice quiz, study plan, and credit details.