Questions & Answers

What’s a black hole? What’s the difference between a reflecting and refracting telescope? This is the place to come for answers to almost every astronomy question you can think of — and many you haven’t. Find answers to your equipment and hobby questions, as well as astronomy facts about the other planets in the solar system, stars, and galaxies.

Is Andromeda Galaxy headed for a clash with the Milky Way? What’s the faintest thing you can see with a ground-based telescope? From stargazing advice to stellar science, take a poke through this Q&A section (or email us with your own question at to deepen your knowledge of astronomy as a hobby and a science.

Kavli Foundation Q&A: Searching for Alien Life with a “Super-Hubble” Space Telescope

Watch a Q&A with two astronomers on the promise of Hubble's successor telescope, courtesy of The Kavli Foundation. Scientists have unveiled a bold proposal for a giant new space-based telescope that would be far more powerful than today's observatories. Called the High Definition Space Telescope (HDST), the instrument is essentially a supersized Hubble Space...

Fermi visualization of Milky Way bubbles

Q&A: Understanding the Fermi Bubbles

Sky & Telescope features a Q&A between The Kavli Foundation and three astrophysicists who discovered two enormous and unexpected structures radiating from the center of our galaxy. They discuss what these mysterious bubbles can tell us about the history of the Milky Way and how they could help in the search for dark matter.

Closed universe (top), open universe (middle), and flat universe (bottom). 

Is space flat or curved?

Locally, spacetime is curved by the presence of massive objects. The total mass and energy density of the universe also has an effect on the overall curvature of space.

The dark matter concentrations in the galaxy cluster Abell 1689 are tinted blue. Astronomers determined the location of those concentrations from gravitational lensing.
NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)

What is dark matter?

Dark matter is a mysterious type of matter that doesn't interact with any form of electromagnetic radiation, i.e., light. Although we’ve never detected dark matter directly, a large amount of evidence points to its existence.

Supermassive black hole, NASA/JPL-Caltech

How big is a black hole?

Black holes are singularities: points of infinitely small volume with infinite density. However, the amount of a mass concentrated in a black hole varies, and the mass determines how wide the black hole's sphere of influence is.

Two-dimensional representation of the three-dimensional curvature of spacetime around a massive object. 

Are black holes real? If so, who discovered them?

The concept of a black hole was first contrived in by John Michell 1783. For a long time, many notable scientists, including Albert Einstein, believed black holes were merely theoretical. However, in the last century, astronomers have gathered a good deal of observational evidence for the existence of black holes.

Map of the eras of the Big Bang. 

How did the universe begin? What happened during the Big Bang?

The Big Bang marked the beginning of the universe's expansion from a singularity — a single point that was infinitely small, infinitely hot, and infinitely dense. Cosmologists have designated several distinct eras for the universe's evolution from the first moments after the Big Bang to a billion years later.

Our expanding universe

What is dark energy?

Cosmologists have invoked the concept of dark energy to explain the accelerated expansion of the universe, but the nature of dark energy remains one of the most pressing questions facing modern cosmology.