Comments on: Ooooo, pretty! And a little scary.

By: Mark Good

Mark Good — Fri, 24 Oct 2008 10:54:53 +0000

What is the astrological significance of 12/21/2012 ?

By: TheWalruss

TheWalruss — Thu, 23 Oct 2008 07:30:54 +0000

SteveG – that things happen when we see them because of relativity is actually what I was thinking when I first considered this problem after reading the “blobs” post I mentioned. I’m glad I got to the right conclusion then, even though I rolled it back afterwards because it was difficult to grok!

Buzz – You make a very good point there! It’s even more poignant when we consider that not all scientists agree on the distance to all the objects out there – how could two disagreeing scientists discuss a particular event if one calls it “the supernova of ‘69″ and the other “the supernova of ‘41″? The timing of observations is much easier to agree on.

By: Buzz Parsec

Buzz Parsec — Thu, 23 Oct 2008 04:16:17 +0000

P.S. That was a made-up fact for illustrative purposes only. I’m not sure which SNR Walruss was talking about, nor if Herschel ever saw it. Don’t try this at home!

By: Buzz Parsec

Buzz Parsec — Thu, 23 Oct 2008 04:14:20 +0000

SteveG, good explanation.

A second reason for referring to events as happening when we see them is that we know, pretty precisely, when we saw them, but we don’t know the differences to most astronomical objects very accurately at all. If we start talking about what happened in 8320BC based on the assumption that the supernova we saw in 1680 is 10000 lightyears away, and it turns out to be 9200 ly, then we have to re-write all our descriptions, and as the distance is revised, you would have to know what the accepted distance was when whatever you are reading was written, and correct for it. It’s much easier if you just say “It exploded in 1680 and in 1783, William Herschel observed it as a disk of about 7.5″ in diameter.”

By: Yelena

Yelena — Wed, 22 Oct 2008 23:03:50 +0000

There are some really freaking huge binaries in R136, too, though that’s in the LMC. A few years ago, when I was an undergrad, I was crunching data from R136 and found a pair of huge O-type stars that orbit each other with a period of slightly less than 2 days. 2 days! That was exciting.

By: Melusine

Melusine — Wed, 22 Oct 2008 19:00:14 +0000

Sure is pretty. Reminds me that the November National Geographic has an article on light pollution.

By: SteveG

SteveG — Wed, 22 Oct 2008 18:06:55 +0000

Jsug, Redex, theWalrus,

You might consider Einstein’s definition of simultaneity particularly for observers separated by large distances. I’m no expert but my understanding is that things indeed do happen when we see them. Yes we are looking back in time – sort of. The event happened a long time ago – if you were there. And if you were there you could travel at the speed of light (along with the light from the star) and tell us about it when you got here. However, we would age how ever many years it took, and you would not. For you it happened a second ago. For us a second ago. Only for us a lot of time has gone by and we’re a lot older.

There is no way to go back in time. For us these events happen when the light reaches us.

This website has an interesting animation and discusses the idea of simultaneity over large distances and even over the 385,693km between the earth and moon during the first lunar landing.

http://www.fourmilab.ch/documents/RelativityOfSimultaneity/

Perhaps someone else can correct me or better explain it (?)