## Light has no mass so it also has no energy according to Einstein, but how can sunlight warm the Earth without energy?

Although it is true that light has no mass, it does in fact carry energy. This answer is a little more complex than that simple statement though and may require you to have a little basic knowledge on Einstein’s theory of special relativity: the theory that can explain how space and time are linked. E … Read more Light has no mass so it also has no energy according to Einstein, but how can sunlight warm the Earth without energy?

## Is the Sun yellow or white?

I’ve heard multiple sources say the sun is white, that it just looks yellow because the Earth’s atmosphere is scattering the blue light. I’ve heard in other places that the sun is yellow because of its position in the Hertzsprung-Russell (H-R) Diagram. Which is it? It can’t be both yellow and white at the same … Read more Is the Sun yellow or white?

## How long does it take for stars to explode?

I understand stars are millions of light years away and it takes a long, long time for the light of say a star exploding to reach us. We have pictures of stars exploding 50 years ago. Why are those stars still exploding? Do they explode in slow motion?? Also, why don’t we see galaxies turning? … Read more How long does it take for stars to explode?

## How much of the Sun has been used up?

That’s a very interesting question, and one that can often be very difficult to answer when getting deep into the details, but I’ll try and do a quick “back-of-the-envelope” calculation for you and mention when these tricky little details might become important and change my answer. Here is the basic problem to solve. The Sun … Read more How much of the Sun has been used up?

## Is Betelgeuse shrinking?

I read that Betelgeuse is shrinking. Is it true, and will there be any consequences? Betelgeuse is a star very often studied by astronomers. Before answering why Betelgeuse is shrinking, let’s explain how to keep a star in a stable state. To do that, two forces must be in equilibrium: gravity, which pulls inward and tries … Read more Is Betelgeuse shrinking?

## Do single stars tend to rotate in the same direction as the Sun and/or the Galaxy?

Do single stars tend to rotate in the same direction as the Sun and/or the Galaxy? This is a more technical question, so I am going to give a more technical answer, but first the simple answer. No, the rotation of a single star is not aligned with the galactic rotation because there are more … Read more Do single stars tend to rotate in the same direction as the Sun and/or the Galaxy?

## What is the difference between “twin suns” and “binary suns”?

Thanks for the great question! Many people get confused about these two terms as you do. Hopefully I can help clarifying the difference. The dictionary definition of “Twin” is a person or thing that is exactly like each other, or something containing or consisting of two matching or corresponding parts. Therefore, when an article says … Read more What is the difference between “twin suns” and “binary suns”?

## How do astronomers zero in on the spectrum of a single star?

How can astronomers zero in on one single star for spectral analysis yet be sure they are not receiving light pollution from other stars in the field of view? Before the spectrum is taken, we are usually able to image the star field and we can also image the position of the slit, which lets … Read more How do astronomers zero in on the spectrum of a single star?