Is the Sun a variable star?

[yeletah]

Hi

Quick question, is the sun a type of variable star, increasing slightly in brightness every 11 years as seen from a different region of the Milky Way?

(Or is a solar max not actually any brighter than a solar min)

[lukebl]

As far as I understand it, yes, the sun is very variable. Which is why we have ice ages and climate change. But linking climate change to anything other than totally human intervention is currently considered heresy, so I'd better shut up now!

[gazza63]

Hi Luke

I'm with you on that one.

Regardless of humans being on this planet or not...we would still have climate change.

[JB80]

I thought the Sun link to ice ages is more to do with our orbit and being further out so to speak.

I would of said our Sun is fairly stable.

Right, now off to check.

[ronin]

It is but the period is very long, equally I would expect all stars to be variable to an extent.

Our sun has changed over time but we are talking about 4 to 4.5 billion years, during which time the mass and composition of the sun has altered.

The sun is considered to be a fairly stable star, at least during this period of it's life. Had it not been stable it is considered likely that life or at least life of the order we are would not have evolved.

So to an extent the question is what rate of change needs to be present to be counted as variable.

[JB80]

From wiki

Many, possibly most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11 year solar cycle.

So I guess it is a variable star.

You learn something everyday.

What good question though, I like it.

[ronin]

I think JB is correct the earths orbit is part of the reason for ice ages and also that the earths angle to the sun alters over several thousand years and we alter our angle to it. Thus more or less light impacts on the planet - covered in one of the TV programs about the earth a few months back, and that is why I recall it. I think the earths angle oscillates by 2 degrees and it is just sufficent to cause ice ages to occur. Probably to do with the rate of precession.

[Steve Ward]

Some interesting stuff regarding this in the earlier program on BBC2 , worth a look on i-player if you missed it .

http://www.bbc.co.uk/iplayer/episode/b03694kd/The_Secret_Life_of_the_Sun/

[stevepeverall]

I thought the Sun link to ice ages is more to do with our orbit and being further out so to speak.

I've read the same thing.

Also, that European temperatures have historically been liked to sunspot activity. Sunspot activity has been recorded for over 500 years ever since Galileo's day. During the 17th century there was a sunspot minimum called The Maunder Minimum which lasted for about seventy years. This roughly overlapped with the rule of one Louis XIV of France and this period was characterised by a prolonged period of blisteringly hot summers and cold winters in Europe and that this is why Loius XIV was known as 'The Sun King.'

We need a climatologist to chime in on this subject.

[stevepeverall]

There was a BBC Horizon programme on this back in th 70s.

http://avaxho.me/video/Format/documentary/bbc_horizon_the_sunspot_mystery_1977.html

[Steve Ward]

On YT here .... http://www.youtube.com/watch?v=vZVsoSvDmm0

[stevepeverall]

On YT here ....

Good work Steve! I feel compelled to watch it now.

[JamesF]

From where I'm sitting, the Sun is damn variable. I've not seen it for days

If you've not seen it, there was a series broadcast last year(?) called "Orbit" that might be worth looking out. It's a bit hit-and-miss, co-presented by Kate Humble, Liz Bonnin (IIRC) and Helen Czerski, but does cover some interesting ground relating to our climate. I think there was a suggestion that ice ages are trigged by a combination of several factors. Once is related to the Earth's precession. Unfortunately I can't recall what the others are off the top of my head. I think I kept the recordings so I might have to go back and watch them again. I can always skip through Kate Humble and Liz Bonnin's pieces

James

[Polar Bear]

We need a climatologist to chime in on this subject.

I'm no climatologist but I am a reader. The rate of decline of Sunspot activity over the next 3-4 years will be very interesting.

There is a lot of debate out there over whether the Sun is entering a quiet phase, only time and observation will tell.

[umadog]

But linking climate change to anything other than totally human intervention is currently considered heresy, so I'd better shut up now!

Climate scientists are well aware that a variety of non-human factors can have massive effects on the planet's climate. Only people with little knowledge would dispute the fact, so I'd hardly call it "heresy". However, the recent increase in atmospheric carbon dioxide and the resulting climatic changes are widely considered (by climate scientists) to be almost entirely of human origin.

[JB80]

From where I'm sitting, the Sun is damn variable. I've not seen it for days

If you've not seen it, there was a series broadcast last year(?) called "Orbit" that might be worth looking out. It's a bit hit-and-miss, co-presented by Kate Humble, Liz Bonnin (IIRC) and Helen Czerski, but does cover some interesting ground relating to our climate. I think there was a suggestion that ice ages are trigged by a combination of several factors. Once is related to the Earth's precession. Unfortunately I can't recall what the others are off the top of my head. I think I kept the recordings so I might have to go back and watch them again. I can always skip through Kate Humble and Liz Bonnin's pieces

James

That was the show, I remember watching it and that's probably why I remember something along those lines.

It was a good show and well worth a watch if you haven't seen it.

[Polar Bear]

Some interesting stuff here showing the lower predicted amplitude of peak activity.

http://solarscience.msfc.nasa.gov/predict.shtml

[lukebl]

..... However, the recent increase in atmospheric carbon dioxide and the resulting climatic changes are widely considered (by climate scientists) to be almost entirely of human origin.

Yes, I don't doubt that the recent dramatic increase in CO₂ is our doing, and we have somehow got to do something to stop the mess we're making of the planet. So I'm not supporting complacency. However, I think that a significant proportion of people believe that humans are solely to blame for climate change, and that the 'magic bullet' of CO₂ reduction will stop climate change. It clearly won't. We're far too insignificant in cosmological terms. People worry about dealing with a sea level rise of a metre or two. Crikey, there have been times in the past when sea levels were hundreds of metres higher than they are now, and I'm sure that forces way beyond our control will have the same effect sometime again.

Anyway, I digress. Sorry!

[stevepeverall]

A really good link Polar Bear also containing some really good links including this one which shows trends within trends.

http://solarscience.msfc.nasa.gov/images/bfly.pdf

It gives the impression that sunspots need to be measured for millenia to see any big picture.

Getting back to the original OP, the percentage area of sunspots on the suns surface is only a fraction of a percent. Assuming that this is proportional to the suns brightness I guess it might not be that visible from another part of the Milky Way.

bfly.pdf

[stevepeverall]

Crikey, there have been times in the past when sea levels were hundreds of metres higher than they are now, and I'm sure that forces way beyond our control will have the same effect sometime again.

Totally. Its amazing to think that just eight thousand years ago you could walk in a straight line from Newcastle to Denmark!

[yeletah]

Thanks for the posts, a lot to think about!

I take it the sun is stable, but very slightly variable (0.1%) over a 11 year period.

Maybe the internal mechanics of our sun which cause the variability could be applied to other stars that we can see are more variable over a shorter period.

[Peter Drew]

Only if you kept off the Newcastle Brown!

[cjoe]

The climate during the last 10,000 years has been the most stable and slow changing on record which indicates that we're close to an equilibrium. It's no surprise that this coincides with the development of agriculture and civilization as we know it. The climate usually changes very slowly over huge timescales like 100s of 1000s of years but in the most recent 200 years, the rate of change we've measured is relatively rapid, it should take 1000s of years to change by the amount it has since the 19th century. Human industry worldwide produces 135 times the amount of CO2 per year than all of the volcanoes in the world put together.

It's funny because we have the technology to shift over to renewable energy today but the mega funding from the worlds richest still goes into prospecting and mining fossil fuels, I guess it's just easy money for them.

The Milankovitch cycles are known to affect our climate more than solar variation.

[rwilkey]

I have never thought of our Sun as a variable star, and while there is no real definition, any star can be called 'variable' as its light is bound to vary because of it's internal nuclear fusion. However, 'variable' refers to those more distant stars in our universe where the detection of light is seen to be variable, often caused by an eclipsing binary or some other extraneous function that we do not fully understand as yet. No, I would say our home star cannot be regarded as a true variable, as this difintion of 'variable' does not apply to our our Sun because it is too close, also we know it not be an eclipsing binary (not that this is a definition of a variable star) but because it is not distant enough to be seen as a 'variable' in the same way as we describe more distant stars.

[michael.h.f.wilkinson]

The sun is also variable with a period of about 5 minutes, a period corresponding to resonances in the sun. The amplitude is very hard to measure (it is easier to pick up spectrographically). Google "helioseismology" for more. As mentioned above, whether or not you consider the sun a variable star depends on your definition. Note that variability of the output need not directly involve variability in the nuclear reactions. Cepheids may vary a lot in time scales of days, but I gather the nuclear fusion processes cannot change significantly in that time scale.