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The Universe Within 12.5 Light Years

(www.atlasoftheuniverse.com)
266 points algorithmista | 2 comments | 05 Sep 25 22:20 UTC | HN request time: 0.487s | source
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jader201 ◴[06 Sep 25 01:47 UTC] No.45145848[source]▶
Tangential comment, but it’s crazy to think about how, when we look up at the stars in the sky, we’re seeing light in wildly varying degrees of age.

For example, when we look at the sun, that’s 8-minutes-old light. When we look at Polaris (the North Star), that light is 447 years old.

When we look at Andromeda?

Yeah, that light is 2.5 million years old.

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SoftTalker ◴[06 Sep 25 02:34 UTC] No.45146125[source]▶
Light doesn’t age. From its perspective it hit your retina the moment it left the star.
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jb1991 ◴[06 Sep 25 03:05 UTC] No.45146273[source]▶
You are saying, from the perspective of light, whether it travels 1 mile or a trillion miles, that journey takes the same amount of time?
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oneshtein ◴[06 Sep 25 08:47 UTC] No.45147661[source]▶
Yep, this is what he saying, but this is not what photon does. Photon must perform different amount of wave cycles to reach 1 meter or 1 trillion metters. These cycles can be counted.
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1. cryptonector ◴[06 Sep 25 15:28 UTC] No.45150141[source]▶
> These cycles can be counted.

In a lab setting, yes, but across such distances, no. Photons don't have a cycle counter on them, so they don't keep a cycle count and can't reveal that cycle count. All we can do is measure frequency/wavelength (spectrum, really, since we're going to see lots of photons, not really onesie/twosies) and intensity, and we can use the astrophysical distance ladder to figure out roughly where the emitter must have been.

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2. oneshtein ◴[06 Sep 25 19:02 UTC] No.45151972[source]▶
Red shift allows us to roughly calculate distance and time, so we can multiple time by frequency of light to calculate number of oscillations or cycles and then calculate loss of energy per oscillation at average.