Is the Sun a variable star?

[AlexB67]

May I ask the question to ye atro experts, what qualifies as variable in this case, as it seems to me it refers to the fact that variability in this case refers periodicity, or repeating patterns of sorts, I presume this must be an associated criterion ? Otherwise, in a sense you could say every star is variable from birth to death in some form or other, making the definition a bit pointless.

Or am I over thinking it. This is just sort of common sense coming to me rather than having read about said subject

[michael.h.f.wilkinson]

Periodicity is not needed, as there are several irregular variables and so-called cataclysmic variables out there (R CrB types and flare stars spring to mind). I think astronomers typically called a star variable if the amplitude is at least about 0.1 magnitudes. As sensors got better, this may have moved down a bit. More interesting than calling a star variable is understanding the type, and the mechanism.

[umadog]

May I ask the question to ye atro experts, what qualifies as variable in this case, as it seems to me it refers to the fact that variability in this case refers periodicity, or repeating patterns of sorts, I presume this must be an associated criterion ? Otherwise, in a sense you could say every star is variable from birth to death in some form or other, making the definition a bit pointless.

I think you're right. To some degree, every star is surely variable. But there are some stars that are far more variable than others and whose variability is of a vary particular sort. Look at the Wikipedia page to see how they're classified: http://en.wikipedia.org/wiki/Variable_star So we don't just classify stars into variable and on-variable. The variable stars themselves are classified into multiple sub-categories. For at least some of these, we have a good understanding of mechanism behind the variability. So ultimately, what's interesting scientifically is say that a star exhibits variability of type X and Y and we explanations P and Q for how that works.

[AlexB67]

Periodicity is not needed, as there are several irregular variables and so-called cataclysmic variables out there (R CrB types and flare stars spring to mind). I think astronomers typically called a star variable if the amplitude is at least about 0.1 magnitudes. As sensors got better, this may have moved down a bit. More interesting than calling a star variable is understanding the type, and the mechanism.

Thank you, that makes sense thinking about it, so the term variable is appropriate with a clear definition ... I see now. I guess I was kind of thrown by the fact that often periodic behaviour is thrown into the pot in such discussions.

[ollypenrice]

I think that if we were to observe the Sun at more typical stellar distances we would not generally call it a variable. Having such an intimate relationship with it means that we are far more sensitive in our assessment of its variability. The key point is that it is firmly located in its main sequence phase with a long time to go before it migrates into the giant branch of the HR diagram when it will probably become extremely variable at times.

So my answer to the question would be that the Sun is a stable main sequence star but is, even so, somewhat variable since gravitational pressure/radiation pressure is not a perfect feedback mechanism, though it is a very good one.

Olly

[AlexB67]

I think that if we were to observe the Sun at more typical stellar distances we would not generally call it a variable. Having such an intimate relationship with it means that we are far more sensitive in our assessment of its variability. The key point is that it is firmly located in its main sequence phase with a long time to go before it migrates into the giant branch of the HR diagram when it will probably become extremely variable at times.

So my answer to the question would be that the Sun is a stable main sequence star but is, even so, somewhat variable since gravitational pressure/radiation pressure is not a perfect feedback mechanism, though it is a very good one.

Olly

I guess in the end it is all relative to a degree and agreeing on a definition. It reminds me of the fact that really there are similar discussion in molecular physics, which is more my home turf by background, but a different terminology is often used.

Terms such as steady sate, quasi steady state behaviour, oscillating or periodic behaviour, or simply an evolving system with no real pattern are commonly used, they would all be variable systems of sorts, except for the steady state or equilibrium condition, but even then the dicussion becomes somewhat academic, it isn't that nothing moves around even in a steady sate at a microscopic level, but overall on the macroscopic scale it would be perceived that way and classified as such on the scale that it is observed.

In any case, where the cut off lies is down to a matter of definition, where one overlaps the other and so on, and for that matter to what degree observations can be made to verify such process to make the claim, considering that experimental techniques are constantly moving forward to detect the smallest details and breaking new boundaries.

All in all, the way I see it in some sort of way, as far as a mathematical definition and description goes, it boils down to a common theme in all these disciplines, but different scientific disciplines like to use different terminology. I see where you are coming from. What interests me also, and something that really stands out for me from this thread is that ideas are expressed in different ways. Every discipline has its fair amount of technical jargon

[michael.h.f.wilkinson]

I think that if we were to observe the Sun at more typical stellar distances we would not generally call it a variable. Having such an intimate relationship with it means that we are far more sensitive in our assessment of its variability. The key point is that it is firmly located in its main sequence phase with a long time to go before it migrates into the giant branch of the HR diagram when it will probably become extremely variable at times.

So my answer to the question would be that the Sun is a stable main sequence star but is, even so, somewhat variable since gravitational pressure/radiation pressure is not a perfect feedback mechanism, though it is a very good one.

Olly

Some "stable" main-sequence stars are variables. The instability strip in the Hertzsprung-Russel diagram reaches into the main sequence at A-F stars

[Macavity]

I have heard the Sun described as a (possible) "Flare Star". When, and by whom, I can't remember now.

http://en.wikipedia....wiki/Flare_star

Reading about the mechanism of flare production, and noting last nights program on the Sun, perhaps so?

But at least, thankfully, in a relatively minor and unexciting way?

[ollypenrice]

Some "stable" main-sequence stars are variables. The instability strip in the Hertzsprung-Russel diagram reaches into the main sequence at A-F stars

Thanks Michael. Some enjoyable reading ahead!

Olly

[stevepeverall]

Looks like we've all been hoodwinked...........I knew it!

Looks like a really interesting video Jessun.

[cjoe]

Ah, the great global warming swindle, this old gem, Martin Durkins masterpiece. Has anyone heard about what the scientists he interviewed have said about the film after it was released? They publicly stated how Martin Durkin had misrepresented what they were saying by cutting out the important bits of the interview and only leaving in the bits that fit his agenda.

That's a great story/angle though, Jessun. Especially the bit about coal strikes and nuclear power during Thatchers years, scandalous! but wouldn't you rather trust a scientific concensus over a [dodgy] documentary producers opinion?

Joe

[Polar Bear]

There is a lot of debate out there regarding the whether the rise in CO2 precedes or lags temperature rise. Much research puts CO2 600 years behind temperature,

[pixelsaurus]

The Milankovitch Cycle also has a role to play in climate change.

http://en.wikipedia.org/wiki/Milankovitch_cycles

[michael.h.f.wilkinson]

I have hidden the clearly political comment with the Martin Durkin link. I would like to commend the subsequent contributors for getting the debate back on a scientific track. Please note that it is not the track on which this thread started. Something about a variable stars, I seem to remember. The OP might consider the thread hijacked.

[michael.h.f.wilkinson]

BTW, Polaris is one of the nearest Cepheid variables (if not the nearest). Quite funny in the light of the Gerry Rafferty Lyrics:

"You've been as constant as the Northern Star"

I have just looked at the sun's variations over the 11 year solar cycle, and the amplitude in magnitudes is 0.0008. Well beyond most photometry systems when used on stars. The "solar constant" varies from about 1365.5 to 1366.5 W/m²

[Jessun]

I have hidden the clearly political comment with the Martin Durkin link.

That was my post, and whilst posted linked as someones 'story', that mainly dealt with the past, I acknowledge with hindsight that the post wasn't in line with SGL CoC, and apologize to the OP and the team behind this forum.

/Jesper

[michael.h.f.wilkinson]

That was my post, and whilst posted linked as someones 'story', that mainly dealt with the past, I acknowledge with hindsight that the post wasn't in line with SGL CoC, and apologize to the OP and the team behind this forum.

/Jesper

No worries.

[yeletah]

Great posts, thanks

Regarding the first first film in the thread, Its quite interesting to hear that sun's variability may have contributed

to causing the memorable drought of 1976 which apparently nearly resulted in US crop failures.

Perhaps more time and resources should be spent on understanding the mechanics of the sun rather

than understanding deep space subjects.

[Macavity]

Variation in solar output and sundry correlations have been discussed for a fair old time now? I was prompted to checkout the ID of one of the first (dimly remembered) books I read on Astronomy - My late Dad's, 1950's prototype "BBC Book": The Nature of the Universe by Sir Fred Hoyle. (http://en.wikipedia....wiki/Fred_Hoyle)

Sadly, long "lost in action"! But I do remember a discussion therein re. the Sun "tunneling(?) through different regions of space", picking up variable amounts of "matter" - Solar output / climate changing etc. Not to mention the arrival of 'Flu viruses, Panspermia? Cue Fred / Yorkshire Accent: "And the youth of today think they invented controversy...".

[dragonlord]

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.

As a side note to the OT - The reasons for not shifting over to renewable energy really boil down to 2 reasons 1) Logistics, it doesn't matter how much you do or don't want to switch over, we will still be constrained by our ability to produce and ship the quantities of goods to where they are needed 2) efficiency renewable energy (excluding nuclear) currently cannot provide enough energy for the world to exist with the energy usage that we are currently at, let alone where we will be once china, india, et al. finish industrialising.

Back to the sun.

The problem with the variability of the sun as it affects the earth is that while the difference in output is tiny on paper, when you apply that percentage to the output of the sun and how much energy the earth gets from the sun, is that that tiny number adds up to a very big number, especially when you calculate it over time.

[michael.h.f.wilkinson]

As a side note to the OT - The reasons for not shifting over to renewable energy really boil down to 2 reasons 1) Logistics, it doesn't matter how much you do or don't want to switch over, we will still be constrained by our ability to produce and ship the quantities of goods to where they are needed 2) efficiency renewable energy (excluding nuclear) currently cannot provide enough energy for the world to exist with the energy usage that we are currently at, let alone where we will be once china, india, et al. finish industrialising.

Back to the sun.

The problem with the variability of the sun as it affects the earth is that while the difference in output is tiny on paper, when you apply that percentage to the output of the sun and how much energy the earth gets from the sun, is that that tiny number adds up to a very big number, especially when you calculate it over time.

True, but at the same time, the sun is not as variable as a lot of others out there (fortunately )

[bingevader]

Excellent discussion as always on here!

With regard to climate change/global warming, (slightly different things but never mind) actually we're still on our way out of the last ice age, so yes, the planet is still in a phase of warming.

However, our impact is another thing altogether, and lets face it, you wouldn't pour petrol on your house if it were already burning now would you?

Cheers

[Earl]

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.

I honestly think that depends on who is funding the research.

[JamesF]

I honestly think that depends on who is funding the research.

Or perhaps not:

http://www.nytimes.com/2012/07/30/opinion/the-conversion-of-a-climate-change-skeptic.html?pagewanted=all&_r=0

James