Comment by Joseph P on August 24, 2011 at 5:39pm

The bit about moving between spiral arms of our galaxy is incorrect.  First off, the distance between the arms of the spiral is a freaking huge distance.  We're talking about 10,000 light years here.  If it takes light that long to move that distance, then our solar system would take a couple tens of millions of years.  Most stars move at a snail's pace, relative to light.

 

I was just looking up some information on the subject, after reading your post, and I found http://www.atlasoftheuniverse.com/milkyway.html to be pretty informative.  One section addresses a misconception you had:

 

It should be emphasized that there are almost as many stars between the spiral arms as in the spiral arms. The reason why the arms of spiral galaxies are so prominant is that the brightest stars are found in the spiral arms. Spiral arms are the major regions of star formation in spiral galaxies and this is where most of the major nebulae are found.

 

Even before I found that page, I was going to say that the other stars have pretty much zero impact on our planet, from a heating perspective.  The next star over is the Centauri cluster: Proxima Centauri, α Centauri A, and α Centauri B (that's an Alpha in front of those).  Those three are all a little over 4 light years away from us.

The light from them that has no noticeable effect on our weather patterns.  The light from our sun is so much more than we get from those three stars that the only reasonable way to express it is with exponents.  We're talking something like 10^30 ... 1,000,000,000,000,000,000,000,000,000,000% or so, in other words.

The ice ages are caused by activity changes within our sun.

Comment by George on August 26, 2011 at 2:15am

@ Henriette
"Between which stars can we see the the middle of our own galaxy?"

I'm not sure what you mean by "between which stars", since there are billions of stars clustering around the center of the galaxy. The center of the Milky Way is in the direction of the Sagittarius constellation. The supermassive black hole at the center is believed to be Sagittarius A* which is seen via radio astronomy and is about 26,000 light years away. (Deneb is in the constellation Cygnus)


Re: Ice ages and galactic arms - I've never heard that idea. My first thought was it sounds ridiculous, but I found this article in the SF Chronicle - Ice ages linked to galactic position / Study finds Earth may be coo...

The article references an paper in the by a Professor Douglas Gies in a 2005 issue of the Astrophysical Journal. This turns out to be "Ice Age Epochs and the Sun's Path through the Galaxy". Fortunately the paper is available for free download there.

Comment by Joseph P on August 26, 2011 at 10:22am

Some sort of chain of events perhaps, George? The position of our solar system within the galaxy effects the activity of our sun, which leads to ice ages? As a direct cause, I can't see other stars affecting our world's climates, unless they got within a few times the orbit of Pluto.

Comment by George on August 27, 2011 at 6:33pm

@Joseph: The first page of the SF article explains the basic hypothesis. The issue is cosmic rays bombarding the atmosphere.

The article states that in the spiral arms, there are more supernovae explosions occurring, which produce an increase of cosmic rays. These affect the charges of oxygen atoms in the upper atmosphere, attracting more water vapor and increasing cloud cover.

Not sure how testable that is, but interesting hypothesis.

I'd be interested in seeing how the ice age timeline corresponds with the estimated passage through galactic arms. The galactic year is around 250 million years, so these are very long time periods.

Comment by Joseph P on August 28, 2011 at 6:53am

Yeah, that last bit is what I was mostly thinking about.  The last ice age was about 40,000 years ago, wasn't it?  That isn't much time to move around within our galaxy.

Comment by George on August 28, 2011 at 11:11pm

I'm not familiar with the history of ice ages - from what I'm reading, the terms "Ice age" and "glaciation" are used interchangeably, yet they are different concepts. Technically we're still in an "ice age" but it's an interglacial period. The last glaciation period ended about 20,000 years ago.

http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html

(edited to fix value)

Comment by Joseph P on August 29, 2011 at 6:04pm

No problem.  Also, your English seems fine to me.  I know plenty of native English speakers who are less clean.

Comment by George on September 18, 2011 at 12:05am

This entire cosmic rays and climate change question has become an issue among climate change skeptics:

 

 

It turns out that the so-called "skeptics" didn't even read the scientific paper in question, but jumped to the conclusion they wanted.

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