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- 39-page printable PDF
- 181 terms with examples
- 46 practice questions, answers explained
- 2-page cram sheet and study plans
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DSST® Study Guide
Printable PDF · 39 pages
DSST Astronomy Study Guide
Everything the DSST Astronomy exam tests, in one PDF you can print. Built from Prometric's official outline, heaviest topics first.
- 181 key terms, each with an example
- 46 practice questions with every answer explained
- A 2-page cram sheet for the night before
- 2-, 4- and 8-week study plans built from the exam weights
Last updated 2026 · exam details checked against Prometric's published exam information in 2026
Look inside the guide
Real pages from the 39-page PDF.
What you get for $5
One chapter for each official content area, in the order the exam weighs them.
- 📘39pages, printable
- 🧭8chapters, heaviest first
- 🔑181terms with examples
- ✍️46practice questions, answers explained
- ⚠️24exam traps to avoid
- 📄2page cram sheet
Try 10 free Astronomy questions
In the style of the real exam, from all 8 areas. About 10 minutes, with every answer explained and a score by area.
10 questions
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Question 1 · Planetary Systems: Our Solar System and Others
A newly found comet takes about a million years to orbit the Sun, and its orbit is steeply tilted to the planets' orbits. Where did it most likely come from?
Show the answer
Answer: C. The Oort cloud, a far-off shell that sends comets in from every direction of the sky. Comets with periods of thousands of years or more, on orbits tilted at any angle, fall in from the Oort cloud, a roughly spherical shell far beyond the planets.
The trap: The Kuiper belt is tempting, but it is a flat disk that mainly supplies short-period comets orbiting close to the plane of the planets.
Comets with periods of thousands of years or more, on orbits tilted at any angle, fall in from the Oort cloud, a roughly spherical shell far beyond the planets.
The trap: The Kuiper belt is tempting, but it is a flat disk that mainly supplies short-period comets orbiting close to the plane of the planets.
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Question 2 · Astrophysics
An asteroid orbits the Sun with a semimajor axis of 9 AU. According to Kepler's third law, what is its orbital period?
Show the answer
Answer: B. 27 years. Kepler's third law gives P^2 = a^3. With a = 9 AU, a^3 = 729, and the square root of 729 is 27 years.
The trap: Setting the period equal to the distance (9 years) ignores that the law uses the square of the period and the cube of the distance.
Kepler's third law gives P^2 = a^3. With a = 9 AU, a^3 = 729, and the square root of 729 is 27 years.
The trap: Setting the period equal to the distance (9 years) ignores that the law uses the square of the period and the cube of the distance.
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Question 3 · The Science of Light
A star's spectrum is found to peak at a wavelength of about 1,000 nanometers. Using Wien's law with a constant of 2.9 million nm-K, what is the star's approximate surface temperature?
Show the answer
Answer: D. 2,900 K. Wien's law gives T = 2,900,000 / wavelength. Dividing 2,900,000 by 1,000 gives 2,900 K, a cool star that peaks in the infrared.
The trap: 5,800 K is the Sun's temperature, which peaks near 500 nm. A peak at twice that wavelength means half the Sun's temperature.
Wien's law gives T = 2,900,000 / wavelength. Dividing 2,900,000 by 1,000 gives 2,900 K, a cool star that peaks in the infrared.
The trap: 5,800 K is the Sun's temperature, which peaks near 500 nm. A peak at twice that wavelength means half the Sun's temperature.
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Question 4 · The Sun and Stars: Nature and Evolution
Astronomers photograph the Sun's surface and see a pattern of bright cells, each about the size of Texas, that change over minutes. What do these cells show?
Show the answer
Answer: A. Hot gas rising to the surface in the convection zone. Bright granules are the tops of rising columns of hot gas, with cooler gas sinking between them. This is convection, the way energy crosses the Sun's outer interior.
The trap: Heat spreading by contact describes conduction, which is far too slow in the Sun's gas to carry its energy outward.
Bright granules are the tops of rising columns of hot gas, with cooler gas sinking between them. This is convection, the way energy crosses the Sun's outer interior.
The trap: Heat spreading by contact describes conduction, which is far too slow in the Sun's gas to carry its energy outward.
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Question 5 · Celestial Systems
Which statement best explains why the northern hemisphere is warmer in June than in December?
Show the answer
Answer: C. Earth's axis tilts the northern hemisphere toward the Sun in June. Earth's axis is tilted, so in June sunlight strikes the northern hemisphere more directly and for more hours each day.
The trap: Earth is actually closest to the Sun in early January, and its distance changes by only about 3 percent over the year, so distance is not the cause.
Earth's axis is tilted, so in June sunlight strikes the northern hemisphere more directly and for more hours each day.
The trap: Earth is actually closest to the Sun in early January, and its distance changes by only about 3 percent over the year, so distance is not the cause.
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Question 6 · Galaxies
A star's measured parallax is 0.05 arcsecond. What is its distance from the Sun?
Show the answer
Answer: B. 20 parsecs. Distance in parsecs is 1 divided by parallax in arcseconds: 1 / 0.05 = 20 parsecs, which is about 65 light-years.
The trap: 0.05 parsecs comes from reading the parallax angle itself as a distance rather than taking its reciprocal.
Distance in parsecs is 1 divided by parallax in arcseconds: 1 / 0.05 = 20 parsecs, which is about 65 light-years.
The trap: 0.05 parsecs comes from reading the parallax angle itself as a distance rather than taking its reciprocal.
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Question 7 · The Universe: Contents, Structure, and Evolution
A galaxy is receding at 14,000 km/s. If the Hubble constant is 70 km/s per megaparsec, how far away is the galaxy?
Show the answer
Answer: D. 200 megaparsecs. Hubble's law gives d = v / H. Dividing 14,000 by 70 gives 200 megaparsecs.
The trap: Multiplying speed by H (980,000) uses the law backward; the distance is the speed divided by the Hubble constant.
Hubble's law gives d = v / H. Dividing 14,000 by 70 gives 200 megaparsecs.
The trap: Multiplying speed by H (980,000) uses the law backward; the distance is the speed divided by the Hubble constant.
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Question 8 · Introduction to the Science of Astronomy
A newspaper column says that people born under one constellation will soon "meet someone who changes their life", with no time or details given. Why is this claim not scientific?
Show the answer
Answer: A. No possible observation could show it to be wrong. A claim that cannot be contradicted by any observation is not falsifiable, so it cannot be tested scientifically.
The trap: Predicting the future is not the problem; scientific claims also predict future events. The issue is that this claim could never be shown wrong.
A claim that cannot be contradicted by any observation is not falsifiable, so it cannot be tested scientifically.
The trap: Predicting the future is not the problem; scientific claims also predict future events. The issue is that this claim could never be shown wrong.
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Question 9 · Planetary Systems: Our Solar System and Others
Why did the inner solar system produce only small, rocky planets, while the outer solar system produced giants?
Show the answer
Answer: D. Beyond the frost line, ice could condense, so cores grew massive enough to hold hydrogen and helium. Only rock and metal could condense near the Sun. Beyond the frost line, ice added much more solid material, so cores grew large enough to gravitationally capture nebular gas.
The trap: The claim that the Sun blew gas away reverses the cause: the outer disk was rich in material, which is why giants could build up.
Only rock and metal could condense near the Sun. Beyond the frost line, ice added much more solid material, so cores grew large enough to gravitationally capture nebular gas.
The trap: The claim that the Sun blew gas away reverses the cause: the outer disk was rich in material, which is why giants could build up.
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Question 10 · Astrophysics
A comet is moving fastest at one point in its elliptical orbit around the Sun. Where is the comet at that moment?
Show the answer
Answer: C. At the point closest to the Sun. By Kepler's second law, a planet or comet sweeps equal areas in equal times, so it must move fastest where it is closest to the Sun, at perihelion.
The trap: The point farthest from the Sun is aphelion, where the comet moves slowest. The speed is highest when the distance is smallest.
By Kepler's second law, a planet or comet sweeps equal areas in equal times, so it must move fastest where it is closest to the Sun, at perihelion.
The trap: The point farthest from the Sun is aphelion, where the comet moves slowest. The speed is highest when the distance is smallest.
The DSST Astronomy exam at a glance
The DSST Astronomy exam is a 120-minute, computer-based test from Prometric with about 100 multiple-choice questions. A score of 400 on the 200–500 scale earns an ACE credit recommendation of 3 semester hours, though each college sets its own policy. The exam covers 8 content areas; the heaviest is Planetary Systems: Our Solar System and Others at 20%.
- Questions
- About 100multiple choice
- Time
- 120 minabout 72 seconds a question
- Passing score
- 400on a 200–500 scale
- ACE credit
- 3semester hours
- Exam fee
- $100paid to Prometric
- Calculator
- Nonot allowed
Source: official DSST Astronomy exam page.
What the exam covers
8 areas, heaviest first. The guide's chapters follow this order.
- Planetary Systems: Our Solar System and Others20%
- Astrophysics15%
- The Science of Light15%
- The Sun and Stars: Nature and Evolution15%
- Celestial Systems10%
- Galaxies10%
- The Universe: Contents, Structure, and Evolution10%
- Introduction to the Science of Astronomy5%
How it works
- 1Buy once, $5Secure checkout. No subscription needed.
- 2Download the PDFFrom your TransferCredit.org account, right away and any time later.
- 3Study the heaviest areas firstFollow the 2-, 4- or 8-week plan, then read the cram sheet the night before.
Questions students ask
What's in the full DSST Astronomy study guide?
39 pages: 8 chapters, one per official content area, heaviest first. 181 terms, each with a plain-English definition and an example, 34 key people, common traps and memory tricks, 46 practice questions with an answer key that explains every answer, question tactics, 2-, 4- and 8-week study plans and a 2-page cram sheet.
How much is the full DSST Astronomy study guide?
The full 39-page PDF is $5, a one-time payment. The 10 practice questions on this page are free, with no account.
What does the $29 plan include?
$29 a month gives you all DSST subjects: every DSST study guide plus the full prep course for each subject, and you can cancel anytime. If you only need this exam, the guide on its own is a one-time $5.
How do I get the full guide?
Choose Buy this guide ($5) and check out. Then sign in to your TransferCredit.org account, then open the course and its Download Your Study Guide lesson. The PDF is yours to keep, and you can download it again from your account at any time.
Can I print the guide or use it on my phone?
Yes. It's a PDF, so it opens on phones, tablets and computers, and printing is allowed. Its tick boxes and answer bubbles work in PDF readers that support forms. Copying and editing are turned off.
Is this an official DSST study guide?
No. DSST® is a registered trademark of Prometric, which was not involved in producing this guide and does not endorse it. TransferCredit.org is independent. We built the guide from the official exam outline, and the exam details were checked against Prometric's published exam information in 2026.
Why is this study guide better than a generic review?
It follows the official outline area by area and spends the most pages on what the exam weighs most. Every term comes with an example, each chapter names the traps the exam sets, and the answer key explains why the most tempting wrong answer is wrong, not just which answer is right. It ends with a 2-page cram sheet for the night before.
What is the DSST Astronomy exam?
The DSST Astronomy exam is a 120-minute, computer-based test from Prometric with about 100 multiple-choice questions. A score of 400 on the 200–500 scale earns an ACE credit recommendation of 3 semester hours, though each college sets its own policy. The exam covers 8 content areas; the heaviest is Planetary Systems: Our Solar System and Others at 20%.
More questions about the DSST Astronomy exam (22)
How many questions are on the DSST Astronomy exam, and how long is it?
It has 100 questions to be answered in 2 hours. Some questions are pretest questions that will not be scored.
What is the passing score for DSST Astronomy?
The passing score is 400 on a 200–500 scale. At 400 or above, the American Council on Education (ACE) recommends 3 semester hours. Each college sets its own passing score and credit award, so check your school's policy before you book.
How much does the DSST Astronomy exam cost?
The exam fee is $100, paid to Prometric. Test centers may add their own administration fee. Eligible U.S. military service members can usually test for free through DANTES.
How many college credits is DSST Astronomy worth?
ACE recommends 3 semester hours for a passing score of 400. Your college decides how many credits it awards and which course they replace. Check your college's policy.
Can I use a calculator on the DSST Astronomy exam?
No. This exam doesn't allow a calculator.
Is there a penalty for guessing on DSST Astronomy?
No. Your score counts only correct answers, so a wrong answer costs nothing. Never leave a question blank: rule out what you can and pick your best guess.
What topics are on the DSST Astronomy exam?
8 content areas, from the official outline: Planetary Systems: Our Solar System and Others (20%); Astrophysics (15%); The Science of Light (15%); The Sun and Stars: Nature and Evolution (15%); Celestial Systems (10%); Galaxies (10%); The Universe: Contents, Structure, and Evolution (10%); Introduction to the Science of Astronomy (5%).
Which DSST Astronomy topics should I study first?
Start with the three heaviest: Planetary Systems: Our Solar System and Others (20%), Astrophysics (15%) and the Science of Light (15%). Together they are about 50% of the exam, roughly 50 of 100 questions. The guide's chapters run in that order, heaviest first.
Is the DSST Astronomy exam hard?
It depends on what you already know. No single area dominates: the largest, Planetary Systems: Our Solar System and Others, is 20% and the smallest, Introduction to the Science of Astronomy, is 5%, so broad coverage matters more than deep expertise in one topic. Take the free diagnostic above to see where you stand in about 10 minutes.
What kinds of questions are on the DSST Astronomy exam?
The guide sorts them into 5 types: “Name the term”, “Best illustration”, “Cause and effect”, “Quick calculation” and “Sequence and classification”. Every question has 4 answer choices. Try the 10 free questions above to see the style.
How long should I study for DSST Astronomy?
Use the diagnostic to decide. If you already know most areas, two weeks of daily review is often enough; if the subject is new to you, plan on eight. The full guide has 2-, 4- and 8-week plans built from the exam weights.
How should I pace myself on the DSST Astronomy exam?
On average you have about 72 seconds per question (120 minutes for 100 questions). Be past question 33 a third of the way through and past question 67 two-thirds through. If a question takes more than a minute, pick your best guess, mark it and come back.
What happens if I don't pass DSST Astronomy?
You can retake a DSST exam after 30 days. Use the wait to work through the areas the score report and the diagnostic show you missed.
Do colleges accept DSST Astronomy for credit?
DSST exams are accepted at more than 1,500 colleges and universities, but each school decides which exams it accepts, the score it requires and the credit it gives. Look up your college's DSST policy before you book.
How up to date is this DSST Astronomy guide?
Last updated 2026. The exam details were checked against Prometric's published exam information in 2026. Exams change, so confirm the details on the official exam page before you register.
What should I do the night before the exam?
Read the cram sheet once, slowly. Check your test time, the location or remote-proctoring setup, and the ID you need. Then sleep: a rested brain recalls more than a crammed one. In the morning, skim the memory tricks and common traps, then stop studying.
How much math is on DSST Astronomy?
Very little calculation. You should understand relationships like Kepler's third law, the inverse-square law and Wien's law, but the questions focus on concepts.
Do I need to know physics for DSST Astronomy?
Some. Astrophysics is 15% of the exam and covers Kepler's laws and orbits, Newtonian physics and gravity, and relativity. The official sample questions include identifying an example of Newton's third law, so know Newton's laws of motion and gravitation conceptually.
Does DSST Astronomy cover the Big Bang and cosmology?
Yes. The universe area is 10% of the exam and covers galaxy clusters and large-scale structure, the Big Bang and Hubble's law, the evolution and fate of the universe, and dark matter and dark energy.
What should I know about the H-R diagram for DSST Astronomy?
The Hertzsprung-Russell diagram plots stars' luminosity against surface temperature. Most stars fall on the main sequence because stars spend most of their lives there fusing hydrogen, while giants and supergiants sit above it and white dwarfs below. It underpins questions on stellar classification and life cycles in the Sun and stars area, 15% of the exam.
Does DSST Astronomy include a lab?
No. There's no lab component. Some colleges require a separate lab if they count the credit as a lab science.
Can I take DSST Astronomy online?
Yes. DSST exams can be taken at a test center or online with a remote Prometric proctor.
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DSST® is a registered trademark of Prometric, which was not involved in producing this guide and does not endorse it. TransferCredit.org is independent and not affiliated with Prometric. © 2026 UPI Globale Edu Inc.