Something I don't understand about astronomy and distance to objects.
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06-04-2013, 03:46 PM
Something I don't understand about astronomy and distance to objects.
Recently Hubble spotted a Type 1A supernova measured at 10 billion light years away. Of course this means that it took 10B years for the light from this star to reach us. Meaning the star itself exploded 10B years ago making this one of the oldest stars in the universe. My issue with this is that 10B years ago when this star exploded it was far closer to the Milky Way than it is now. The distance between us and this star is probably thousands or even millions of times farther than it was when this star formed. Why have I never seen a formula that takes into consideration the expansion of the universe when dating objects of a particular distance. If this star is really 10B light years away then it can't possibly have exploded 10B years ago. When it exploded it might have only been 1B light years away and that would affect when we would see it. And since the speed of an object has no affect on the speed of light emitting from that object (and the universe doesn't expand faster than light anyway) it couldn't have moved away from us fast enough to take the light longer to get here.

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06-04-2013, 03:53 PM
RE: Something I don't understand about astronomy and distance to objects.
I don't know the answer, but that's a very good question!! And I'm surprised I've never heard any of my fave's from the Science channel say anything about it. Particularly since I've heard over and over how the universe is expanding, and how this star or that outside the Milky Way is "X" amount of light years from us. Lets hope an astrophysicist happens across this thread!

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06-04-2013, 03:54 PM
RE: Something I don't understand about astronomy and distance to objects.
In fact, anybody know a site like, "Ask-a-Physicist.com"?

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06-04-2013, 04:38 PM
RE: Something I don't understand about astronomy and distance to objects.
You have to factor in the expansion rate of the universe. Space itself is expanding between our telescope and the supernova, and that affects the time it takes the light to reach us.
And since this expansion rate is increasing, eventually we won't be able to see any stars outside of our galaxy.
ANd someday, that expansive force will blow apart our galaxy, and whatever remains of our solar system, down to, I understand, the molecular bonds.

And I want to caveat this by saying I'm merely a keen idiot, and could be completely wrong here.
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06-04-2013, 10:30 PM
RE: Something I don't understand about astronomy and distance to objects.
(06-04-2013 03:46 PM)germanyt Wrote:  Recently Hubble spotted a Type 1A supernova measured at 10 billion light years away. Of course this means that it took 10B years for the light from this star to reach us. Meaning the star itself exploded 10B years ago making this one of the oldest stars in the universe. My issue with this is that 10B years ago when this star exploded it was far closer to the Milky Way than it is now. The distance between us and this star is probably thousands or even millions of times farther than it was when this star formed. Why have I never seen a formula that takes into consideration the expansion of the universe when dating objects of a particular distance. If this star is really 10B light years away then it can't possibly have exploded 10B years ago. When it exploded it might have only been 1B light years away and that would affect when we would see it. And since the speed of an object has no affect on the speed of light emitting from that object (and the universe doesn't expand faster than light anyway) it couldn't have moved away from us fast enough to take the light longer to get here.

They do take into account the expansion of the universe when determining this figure. It's called Redshift and it has to do with the Doppler Effect. You can gauge the relative velocity of stellar objects based on the wavelength of the light they return, that can be taken into account to determine an objects approximate current position in space.

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06-04-2013, 10:55 PM
RE: Something I don't understand about astronomy and distance to objects.
(06-04-2013 10:30 PM)Carlo_The_Bugsmasher_Driver Wrote:  
(06-04-2013 03:46 PM)germanyt Wrote:  Recently Hubble spotted a Type 1A supernova measured at 10 billion light years away. Of course this means that it took 10B years for the light from this star to reach us. Meaning the star itself exploded 10B years ago making this one of the oldest stars in the universe. My issue with this is that 10B years ago when this star exploded it was far closer to the Milky Way than it is now. The distance between us and this star is probably thousands or even millions of times farther than it was when this star formed. Why have I never seen a formula that takes into consideration the expansion of the universe when dating objects of a particular distance. If this star is really 10B light years away then it can't possibly have exploded 10B years ago. When it exploded it might have only been 1B light years away and that would affect when we would see it. And since the speed of an object has no affect on the speed of light emitting from that object (and the universe doesn't expand faster than light anyway) it couldn't have moved away from us fast enough to take the light longer to get here.

They do take into account the expansion of the universe when determining this figure. It's called Redshift and it has to do with the Doppler Effect. You can gauge the relative velocity of stellar objects based on the wavelength of the light they return, that can be taken into account to determine an objects approximate current position in space.

Then why have I heard dozens or even hundreds of times objects seen millions or billions of light years away referred to as millions or billions of years old? I understand redshift but I've never once heard it used to gauge age of objects relative to their distance. Also, if we are receiving the light from the location it was when it exploded then how could an object that exploded 10 billion years ago appear 10 billion light years away? If I throw a baseball at the Andromeda galaxy at the speed of light as I travel in any up, down, left, right direction you will receive the baseball from the location I threw it. Not from the location I've moved to. So an object like a star that has exploded and is visible to us is being viewed from the location it was when it exploded. Not from the location it is now. This particular star which is being called 10B years old would actually be 10B years old plus the distance it's traveled over the last 10B years. So a couple things must be considered. Either this star isn't really 10B light years away or 10B years old and our calculations are off. Or it was a short lived star. Our own sun has a life span of about 7 billion years. If the universe is 13.8B years old then this star must have formed very, very quickly after the BB and live a few billion years at most before going supernova. That still doesn't solve the problem because the universe wasn't nearly the size it is now 10B years ago. If this star is really 10B light years away that tells me that this star hasn't been in that location for 10B years. Making it former location much farther than 10B light years away.

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06-04-2013, 10:59 PM
RE: Something I don't understand about astronomy and distance to objects.
I just emailed the Hayden Planetarium where Dr. Tyson works to get an answer.

“Whenever you find yourself on the side of the majority, it's time to pause and reflect.”

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06-04-2013, 11:18 PM (This post was last modified: 06-04-2013 11:24 PM by Bucky Ball.)
RE: Something I don't understand about astronomy and distance to objects.
As Carlo said, it's the redshift.
The expansion rate is not a constant.
http://map.gsfc.nasa.gov/universe/uni_expansion.html
http://curious.astro.cornell.edu/questio...number=575












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06-04-2013, 11:47 PM
RE: Something I don't understand about astronomy and distance to objects.
So an object like a star that has exploded and is visible to us is being viewed from the location it was when it exploded. Not from the location it is now.

I think I get what you are asking, except I don't think you meant that second sentence. It exploded, it is not in any location now.

What Carlo said; redshift. The universe is not a constant and red shift measurement compensates for the accelerating expansion. Consider At least, I would think so. But I'm not an Astrophysicist. Shy

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07-04-2013, 01:53 AM
RE: Something I don't understand about astronomy and distance to objects.
Space expands faster than the speed of light.

http://curious.astro.cornell.edu/questio...number=575
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