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Tarkus
2009-Jan-28, 02:00 AM
The sun is radiating more as it ages right...

Has this been measured or is this theory?

Do we have data that the earth is warmer than it was 100 years ago?

Peter B
2009-Jan-28, 02:09 AM
G'day Tarkus

I think the mechanism which causes the Sun to gradually increase its output over its lifetime can't be accurately tracked over timeframes as short as a century. It'd be like comparing the output of a 5 hour campfire at two points in time separated by a millisecond (or thereabouts). I'm pretty sure the mechanism is well understood, but I'm also pretty sure there are other cycles which are more dominant on shorter time frames.

Remember, in the Sun's lifetime, a century represents 1 part in about 46 000 000, or about 0.000002% of its life. Given that I understand the Sun's output has increased by about 10% in 4.6 billion years, one century's worth of that would be infinitesimal.

antoniseb
2009-Jan-28, 02:10 AM
The sun is radiating more as it ages right...
Has this been measured or is this theory?

This is observed by looking at other stars in groups that are known/thought to have formed at the same time as each other (globular clusters and open clusters).

By mapping the color vs. magnitude of each cluster it's been observed that older stars of certain masses are brighter than younger stars, until they get to near the end of their Sun-like life.

The change is very slow, and 100 years makes little difference.

Tarkus
2009-Jan-28, 07:27 AM
Oh ok....

We probably wont see any increase in our lifeline then...

AonSao
2009-Jan-28, 07:31 AM
Do we have data that the earth is warmer than it was 100 years ago?

That data exists, but it is not because of an increase in sun radiation. It's b/c the carbon dioxide levels in our atmosphere have increased significantly. You can thank fossil fuels for that one :)


The sun is radiating more as it ages right...

I don't have a source to back this up, but I believe it will stay consistent until it gets low on fuel (hydrogen). When the sun runs low on hydrogen it will begin to swell and radiate a lot more. This event is millions of years away.

EDG
2009-Jan-28, 07:46 AM
I don't have a source to back this up, but I believe it will stay consistent until it gets low on fuel (hydrogen). When the sun runs low on hydrogen it will begin to swell and radiate a lot more. This event is millions of years away.

Yes and no. Yes, it'll eventually turn inot a red giant. No, it's still increasing in luminosity over time while on the main sequence. So much so that in about a billion years time (well before the red giant phase) Earth will be so hot that the climate won't be able to adapt to it and we'll roast.

And technically while it's getting more luminous, the sun is actually getting cooler (and slightly larger) - but the extra luminosity is what will be warming the planets around it more.

AonSao
2009-Jan-28, 08:16 AM
And technically while it's getting more luminous, the sun is actually getting cooler (and slightly larger) - but the extra luminosity is what will be warming the planets around it more.

Increasing the volume would mean there is more surface area. That may be where the extra luminosity comes from. I haven't seen any evidence that its radiation output increases.

Larger volume also means less pressure on the core, and less chances for fusion. Hence, the lower temperature over time?

Edit: Future of our sun

- Volume increases, luminosity increases, temperature cools
- Sun runs low on hydrogen, gravity overcomes the nuclear forces which were previously pushing it outward
- Sun shrinks. Density increases until the sun starts burning its helium
- Outward expansion begins again, but faster and farther (red giant)
- Inner planets are consumed by the sun
- Helium runs low and the sun shrinks again (white dwarf)

http://hubpages.com/hub/About-the-sun

George
2009-Jan-28, 01:57 PM
Given that I understand the Sun's output has increased by about 10% in 4.6 billion years, one century's worth of that would be infinitesimal. I vaguely recall an increase of about 30%.

Spaceman Spiff
2009-Jan-29, 02:05 AM
Yes and no. Yes, it'll eventually turn inot a red giant. No, it's still increasing in luminosity over time while on the main sequence. So much so that in about a billion years time (well before the red giant phase) Earth will be so hot that the climate won't be able to adapt to it and we'll roast.

And technically while it's getting more luminous, the sun is actually getting cooler (and slightly larger) - but the extra luminosity is what will be warming the planets around it more.

For the first ~7 billion years (Gyrs), the Sun's effective surface temperature increases, before decreasing over the remainder of its main sequence phase and then as it evolves to become a red giant. See here (http://arxiv.org/PS_cache/arxiv/pdf/0801/0801.4031v1.pdf), for example (Table 1).

Peter B
2009-Jan-29, 02:52 AM
I vaguely recall an increase of about 30%.

Fair enough.

So I was out by less than one order of magnitude. That's pretty good for physics and astronomy isn't it? ;-)