Astronomy Questions & Answers

What’s a black hole? What’s inside a black hole? What’s the difference between a reflecting and refracting telescope? This is the place to come for answers to almost all the astronomy questions 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, browse this Astronomy Q&A category, browse astronomy questions by topic, or email us with your own question at to deepen your knowledge of astronomy as a hobby and a science.

What are constellations?

In 1930, the International Astronomical Union (IAU) divided the sky into 88 constellations. Each constellation is defined by an imaginary boundary on the sky and named after a classical star pattern within those boundaries. So when we say a star is “in” a particular constellation, we mean it lies within the IAU-defined boundaries of that…

How Do Stars Die and How Long Do Stars Live?

Both the life and death of a star depend on its mass. Generally speaking, the more massive a star, the faster it burns its fuel and the shorter its life. The most massive stars meet their end in a supernova explosion after only a few million years of fusion, while the tiniest stars continue to…

What Is a Star?

A star is a luminous ball of gas held together by its own gravity. Nuclear fusion in its core supports the star against gravity and produces photons and heat. The Sun is the closest star to Earth.

Why Do Stars Twinkle?

Though it wouldn’t work so well in the nursery rhyme, a star’s twinkling actually has a technical term, astronomical scintillation: the effect of our planet’s atmosphere on starlight.

Why do comets have tails?

Comets develop tails as they approach perihelion—the place in their orbits when they are closest to the sun. The sun’s heat causes some of the material in a comet to vaporize, which in turn releases dust particles that were trapped in the ice.

How big is the Sun?

The Sun is more than 330,000 times as massive than the Earth. It has a diameter of nearly 1.4 million kilometers (865,000 miles), and its volume could enclose about 1.3 million Earths.

What is a meteor shower?

Meteor showers occur when Earth passes through a stream of meteoric material. The brief streaks of luminescence we call meteors are caused by meteoroids burning up as they pass through the atmosphere.

Astrology vs Astronomy: What’s the Difference?

The practices of astrology and astronomy have common roots, but they have evolved into two separate fields. Astronomy studies positions, motions, and properties of celestial objects. Astrology attempts to study how those positions, motions, and properties affect people and events on Earth.

What’s Up at Star Parties?

When amateur astronomers and their families plan a vacation, they are increasingly likely to plan it around a star party. The big amateur gatherings have been growing in recent years, and new ones devoted especially to dark-sky observing are sprouting all over. True deep-sky star parties — as opposed to the more traditional, general-interest conventions…

How can a telescope have an f/ratio of f/42?

I was amazed at Jim Melka’s beautiful picture of Mars on page 136 of the January 2006 issue but puzzled by the caption, which said that he used a 12-inch reflector at f/42. How is this possible? Knowing that a telescope’s f/ratio is its focal length divided by its aperture, you’re probably imagining poor Jim…