# The Naked Scientists Forum

### Author Topic: By how much will the Sun grow as it ages?  (Read 2973 times)

#### Francis Tapon

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##### By how much will the Sun grow as it ages?
« on: 12/01/2009 08:45:02 »
Francis Tapon  asked the Naked Scientists:

Astronomers predict that in about 5 billion years, the sun will expand into a red giant briefly and then eventually collapse into a dense,
white dwarf star. I've read this MANY times; however, nowhere have I found the answers to these three questions:

What is the biggest size the Sun in its red giant stage? (i.e., will it engulf the Earth and Mars?)

How long will its red giant stage last? (One week? One year? 1 million years? 1 billion years?)

How long will it be a white dwarf before it runs out of fuel and goes out completely?

Francis Tapon

What do you think?

#### syhprum

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##### By how much will the Sun grow as it ages?
« Reply #1 on: 12/01/2009 10:35:06 »
I can only answer one question with any degree of confidence the Sun in its giant red phase will reach out to the asteroid belt between Earth and Mars but Mars should be spared, as for time certainly millions but billions of years.
White dwarfs are such because they have run out of fuel but they will only cool slowly because of their small surface area.

#### dentstudent

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##### By how much will the Sun grow as it ages?
« Reply #2 on: 12/01/2009 10:38:57 »
I can only answer one question with any degree of confidence the Sun in its giant red phase will reach out to the asteroid belt between Earth and Mars but Mars should be spared

I believe that the sun will reach this distance, but because the gravity of the sun will have changed by then, the actual orbit of the earth will be different. It will have a much larger orbit that now, and so although the sun will reach the current earth's orbit, the earth itself will not be there anymore and so might be spared.

#### Andrew K Fletcher

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##### By how much will the Sun grow as it ages?
« Reply #3 on: 12/01/2009 11:12:48 »
I predict that the sun is decaying and becoming smaller.

#### dentstudent

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##### By how much will the Sun grow as it ages?
« Reply #4 on: 12/01/2009 11:33:18 »
I predict that the sun is decaying and becoming smaller.

I think that you're right at this point, but the natural course of events in the life of a star states that it will eventually become a red giant.

#### dentstudent

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##### By how much will the Sun grow as it ages?
« Reply #5 on: 12/01/2009 11:39:05 »
This is a podcast from Astronomy Cast by Dr Pamela Gay and Fraser Cain. They have been on TNS, so I'm sure that noone will mind a link to their podcasts! This particular one should provide answers to pretty much all of the posted questions.

Astronomy Cast episode 108: The Life of the Sun

« Last Edit: 12/01/2009 11:41:28 by dentstudent »

#### DoctorBeaver

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##### By how much will the Sun grow as it ages?
« Reply #6 on: 12/01/2009 13:45:39 »
I can only answer one question with any degree of confidence the Sun in its giant red phase will reach out to the asteroid belt between Earth and Mars but Mars should be spared, as for time certainly millions but billions of years.

When did the asteroid belt move? It always used to be between Mars & Jupiter.

As for how big the Sun will get, the latest estimate I've seen is that it will not quite, or just, reach Earth's orbit. However, at 200 times its current size it will definitely get close enough to melt the Earth.

HERE is an interesting site.
« Last Edit: 12/01/2009 13:48:57 by DoctorBeaver »

#### DoctorBeaver

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##### By how much will the Sun grow as it ages?
« Reply #7 on: 12/01/2009 13:50:05 »

Ooops, you've just reminded me of something  [:I]

#### The Naked Scientists Forum

##### By how much will the Sun grow as it ages?
« Reply #7 on: 12/01/2009 13:50:05 »