The Top Space Questions

Space is vast, and as far as we know, infinite. Stars, galaxies, planets, and nebulae populate the universe. Space Telescope Science Institute

Astronomy and space exploration are topics that really get people thinking about far away worlds and distant galaxies. When you're out stargazing under a starry sky or surfing the Web looking at images from telescopes, your imagination gets fired up by what you see. If you have a telescope or pair of binoculars, you may well have magnified your view of the Moon or a planet, a distant star cluster, or a galaxy. So, you know what these things look like. The next thing that crosses your mind is a question about them. You muse about those amazing objects, how they formed and where they are in the cosmos. Sometimes you wonder if anyone else is out there looking back at us!  

Astronomers get a lot of interesting queries, as do planetarium directors, science teachers, scout leaders, astronauts, and many others who research and teach the subjects. Here are some of the most-often-asked questions that astronomers and planetarium people get about space, astronomy, and exploration and collected them along with some pithy answers and links to more detailed articles! 

Where does space begin?

The standard space-travel answer to that question puts the "edge of space" at 100 kilometers above Earth's surface. That boundary is also called the "von Kármán line", named after the Theodore von Kármán, the Hungarian scientist who figured it out.

How did the universe begin?

The universe began some 13.7 billion years ago in an event called the Big Bang. It was not an explosion (as is often depicted in some artwork) but more of a sudden expansion from a tiny pinpoint of matter called a singularity. From that beginning, the universe has expanded and grown more complex.

What is the universe made of? 

This is one of those questions that has an answer that will expand your mind as it expands your understanding of the cosmos. Basically, the universe consists of galaxies and the objects they contain: stars, planets, nebulae, black holes and other dense objects. 

Will the universe ever end?

The universe had a definite beginning, called the Big Bang. It's ending is more like the "long, slow expansion". The truth is, the universe is slowly dying as it expands and grows and gradually cools. It will take billions and billions of years to cool completely and stop its expansion. 

How many stars can you see at night?

That depends on many factors, including how dark your skies are where you live. In light-polluted areas, you see only the brightest stars and not the dimmer ones. Out in the countryside, the view is better. Theoretically, with the naked eye and good seeing conditions, you can see around 3,000 stars without using a telescope or binoculars.  

What kinds of stars are out there?

Astronomers classify stars and assign "types" to them. They do this according to their temperatures and colors, along with some other characteristics.  Generally speaking, there are stars like the Sun, which live their lives for billions of years before swelling up and gently dying. Other, more massive stars are called "giants" and are usually red to orange in color. There are also white dwarfs. Our Sun is properly classified a yellow dwarf. 

Why do some stars appear to twinkle?

The children's nursery rhyme about "Twinkle, twinkle little star" actually poses a very sophisticated science question about what stars are. The short answer is: the stars themselves don't twinkle. Our planet's atmosphere causes starlight to waver as it passes through and that appears to us as twinkling. 

How long does a star live?

Compared to humans, stars live incredibly long lives. The shortest-lived ones can shine for tens of millions of years while the old-timers can last for many billions of years. The study of stars' lives and how they are born, live, and die is called "stellar evolution", and involves looking at many types of stars to understand their life cycles. 

What is the Moon made of?  

When the Apollo 11 astronauts landed on the Moon in 1969, they collected many rock and dust samples for study. Planetary scientists already knew the Moon is made of rock, but the analysis of that rock told them about the Moon's history, the composition of the minerals that make up its rocks, and the impacts that created its craters and plains.

What are Moon phases?

The Moon's shape appears to change throughout the month, and its shapes are called the phases of the Moon. They are a result of our orbit around the Sun combined with the Moon's orbit around Earth. 

Of course, there are many more fascinating questions about the universe than the ones listed here. Once you get past the basic queries, others crop up, too. 

What's in the space between stars?

We often think of space as the absence of matter, but actual space is not really all that empty. The stars and planets are scattered throughout the galaxies, and between them is a vacuum filled with gas and dust

What's it like to live and work in space?  

Dozens and dozens of people have done it, and more will in the future! It turns out that, aside from the low gravity, higher radiation hazard, and other dangers of space, it's a lifestyle and a job. 

What happens to a human body in a vacuum?

Do the movies get it right? Well, not actually. Most of them depict messy, explosive endings, or other dramatic events. The truth is, while being in space without a spacesuit WILL kill you (unless you get rescued very, very quickly), your body probably won't explode. It's more likely to freeze and suffocate first. Still not a great way to go.

What happens when black holes collide?

People are fascinated by black holes and their actions in the universe. Until very recently, it's been tough for scientists to measure what happens when black holes collide. Certainly, it's a very energetic event and would give off a lot of radiation. However, another cool thing happens: the collision creates gravitational waves and those can be measured!

Edited and updated by Carolyn Collins Petersen.