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desiraider858
Guest
for example recently a galactic collision was observed at 400 million light years, how was that calculated?? Does this mean that we are seeing something that is 400 million years old??
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phoenixshade
New member
When you get to distances that large, we determine the distance indirectly by measureing the redshift of the incoming light. Since the universe is expanding, everything is moving away from us (at great distances... at nearer distances, gravity is strong enough to overcome this expansion). The further away it is, the faster it moves away.
By measuring the amount of redshift, we can calculate the speed the galaxy is receding. (This works much like the Doppler shift in sound, such as when a speeding car or train passes.) The faster it is receding, the greater the distance. This is known in astronomy as Hubble's Law.
The answer to your second question is yes, if something is 400 million light years away, we are seeing it as it existed 400 million years ago.
By measuring the amount of redshift, we can calculate the speed the galaxy is receding. (This works much like the Doppler shift in sound, such as when a speeding car or train passes.) The faster it is receding, the greater the distance. This is known in astronomy as Hubble's Law.
The answer to your second question is yes, if something is 400 million light years away, we are seeing it as it existed 400 million years ago.
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guanotwozero
Guest
Yes, if we see something 400 light years away, the image we see is 400 years old.
The light year is not calculated, it's just defined to be the distance light travels in a year. To have a value, you just need to know the speed of light and the length of the year.
The speed of light was first measured by Oleus Roemer in 1676 by timing the eclipses of Jupiter's moons at different places in its orbit. Subsequent methods have produced more accurate results.
The length of the year was measured in ancient times, though modern methods give us a more accurate value.
The light year is not calculated, it's just defined to be the distance light travels in a year. To have a value, you just need to know the speed of light and the length of the year.
The speed of light was first measured by Oleus Roemer in 1676 by timing the eclipses of Jupiter's moons at different places in its orbit. Subsequent methods have produced more accurate results.
The length of the year was measured in ancient times, though modern methods give us a more accurate value.
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Patrick
Guest
yes, it would be 400 million years old.
and i believe the way you figure out the distance by triangulation. since we know the radius of the earth you look at the same object in the sky when you are on opposite sides of the planet and measure the angle relative to the line connecting the 2 points you looked at the object from. then you can use some fairly simple trigonometry to find the hypotenuse of that triangle and that is your distance.
and i believe the way you figure out the distance by triangulation. since we know the radius of the earth you look at the same object in the sky when you are on opposite sides of the planet and measure the angle relative to the line connecting the 2 points you looked at the object from. then you can use some fairly simple trigonometry to find the hypotenuse of that triangle and that is your distance.