If our sun was to explode as all stars do eventually, how long would it take for our planet to know? With light traveling at a constant speed I was told that light takes seven minutes to reach earth. Light travels at 299,792,458 m/s. (Hope I'm correct on that). So what amount of time would it take for the suns heat to stop transferring to the earth? Part #2: In which case the sun explodes would the explosion reach earth before we knew what had happened? Would the energy released be string enough to destroy earth? (Probably, but... ). I'm intrested on theories as well. Thank you.

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Originally Posted by tmeunknown

If our sun was to explode as all stars do eventually,

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Not true. Stars of the sun's mass do not explode in a nova, but rather age into a red giant. Not that this detail really matters - when this happens the earth will be incinerated one way or the other. But no mighty explosion is in store for us.

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Originally Posted by tmeunknown

how long would it take for our planet to know? With light traveling at a constant speed I was told that light takes seven minutes to reach earth. Light travels at 299,792,458 m/s. (Hope I'm correct on that).

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Right - so if the sun exploded the first that we'd be aware of it is a bit over 7 minutes after it actually happens.

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Originally Posted by tmeunknown

So what amount of time would it take for the suns heat to stop transferring to the earth?

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I don't understand this question. Do you mean, how long do super novae last?

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Originally Posted by tmeunknown

Part #2: In which case the sun explodes would the explosion reach earth before we knew what had happened?

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We'd first be cooked by a shower of photons that incinerate us, which of course you wouldn't see until they were already here. The blast wave of particles would arrive and mechanically wipe everything out a few minutes later. It would be like being subjected to a nuclear exposion - you're incinerated by the heat before the blast wave tears you apart.

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Originally Posted by tmeunknown

Would the energy released be string enough to destroy earth? (Probably, but...).

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Let's just say it would not be a good day.

Well, I've got a book saying that we have about 5 thousand million years before it becomes a red giant.

But I saw nowhere that our sun will explode, which agrees to what ebaines said.

Let me put it you this way, this will not happen in our lives, or our children's, or our children's children, etc...

I would be more afraid of World war 3.

I had read that a stars mass can implode on itself and cause a supernova, creating a newer, smaller star.
What I was trying to get at was... How long (Minutes, Hours etc.) would a human on earth know that the sun had become a red giant and was about to destroy everything within it's radius. Would it be instantanouse? Also, say we see a giant flash of light. Would the massive heat be slower to reach the earth?

For the sun to become a giant will take time.

According to my book, the sun will gradually become bigger.

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Originally Posted by The Universe by David Bengamini 1968

But long before that (the giant red), rising temperature caused by the sheer weight of ash in its core will start other nuclear processes and the sun will start burning its fuel much faster than it does now. About 5000 million years from now, the speed-up will begin and the sun will start swelling; its output of energy will increase. In another thousand million years (red giant), the average temperature of the earth will rise to something like 550 C, the oceans will boil away and lead will melt like molasses. In the words of Palomar's Allan Sandage, "Conditions will be miserable".

Later, the sun will shrink again, perhaps undergoing its last long death throes, it will continue to shrink while the fires inside it go out and the only glow it emits is energy from the gravitational squeeze of its spent, collapsing matter. Little by little, it will dwindle until it is smaller than the earth, its gases so densely packed that a bucketful of them would weight more than a battleship. For hundreds of thousands of millions of years more, the sun will continue to cool, giving off only infra-red rays. Then it will go out completely, black and cold as the most remote regions of space around it.

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Originally Posted by tmeunknown

I had read that a stars mass can implode on itself and cause a supernova, creating a newer, smaller star.
What I was trying to get at was... How long (Minutes, Hours etc.) would a human on earth know that the sun had become a red giant and was about to destroy everything within it's radius. Would it be instantanouse? Also, say we see a giant flash of light. Would the massive heat be slower to reach the earth?

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In theory IF the sun were to explode, which it won't as previously posted, but IF it did, ebaines hit the nail firmly on the head right here.

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Originally Posted by ebaines

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Originally Posted by tmeunknown

Part #2: In which case the sun explodes would the explosion reach earth before we knew what had happened?

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We'd first be cooked by a shower of photons that incinerate us, which of course you wouldn't see until they were already here. The blast wave of particles would arrive and mechanically wipe everything out a few minutes later. It would be like being subjected to a nuclear exposion - you're incinerated by the heat before the blast wave tears you apart.

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So as photon's travel at the speed of light, after all that's exactly what they are, we'd be cooked about 7 minutes after the sun exploded.
I suppose the "lucky" ones could survive a little longer if they were on the dark side, so shielded from the sun, but the actual explosion would soon finish them off anyway.

So if the sun gradually will get bigger won't it's gravity increase before the heat becomes to intense?

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Originally Posted by tmeunknown

I had read that a stars mass can implode on itself and cause a supernova, creating a newer, smaller star.
What I was trying to get at was... How long (Minutes, Hours etc.) would a human on earth know that the sun had become a red giant and was about to destroy everything within it's radius. Would it be instantanouse? Also, say we see a giant flash of light. Would the massive heat be slower to reach the earth?

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You're confusing super novas and red giants. A nova is what happens to start at least one and a half times out own sun's mass. After the explosion you end up with a high density white dwarf, or for very masive stars a neutron star. But again, this is not in store for our sun.

A red giant occurs when a sun like our own exhausts most of its hydrogen supply, and starts "burning" heavier elements such as helium, carbon, oxygen etc. up through iron. This will start in another 5 billion years or so. The process will take millions of years, so earth's inhabitants will have lots of warning. As part of that process the sun will actually lose much of its mass, which means the force of gravity between earth and sun will be reduced, and the earth's orbit will shift outward - current theories say that our orbit will probably shift enough to avoid being actually engulfed by the sun, but it will be close. Earth will probably become a baked planet much like Mercury is today.

Gravity depends on mass alone (since the distance from the centre is constant), and unless the sun is consuming something that it doesn't have... I don't think that its gravity will increase.

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Originally Posted by tmeunknown

So if the sun gradually will get bigger wont it's gravity increase before the heat becomes to intense?

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Actually its gravity becomes weaker, not stronger, as much of its mass is sloughed off. Recall that the gravitational force between two spheirical objects is proportional to the product of the two masses divided by the square of the distance between the centers of the objects. The center of the sun when it's a red giant will still be 93 miillion miles away, so the denominator of this equation is constant. Thus as the mass of the sun is reduced, so too is the force of gravity between earth and sun, even thouhg the surface of the sun as a red giant is much closer. The result is the earth's orbit shifts outward.

Ebaines is dead on... The sun will go red giant, and take out the first 4 planets the gas giants will then burn up, not a nice day in our little neighborhood.