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29 votes
Accepted

Distance of the Crab nebula and the speed of light

You are absolutely right. The convention is that we date astronomical events by when we see them - which is verifiable, useful and absolutely certain. It wouldn’t be useful to know what year BC it ...
Martin Kochanski's user avatar
20 votes

Distance of the Crab nebula and the speed of light

Just to reiterate my comment. The approach is correct but the accuracy is spurious - the number of significant figures is not warranted by the quality of the distance information (the date of ...
ProfRob's user avatar
  • 155k
9 votes

Distance of the Crab nebula and the speed of light

The distance to the crab nebula is uncertain. It is probably between 4900 and 8100 light years away, (with a best guess of 6500 light years). It is sometimes surprising that astronomers can measure ...
James K's user avatar
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9 votes
Accepted

Why does Helix Nebula look like an eye?

Look at Helix Nebula NGC 7293 (Aquarius) on the left and Ring Nebula M57 (Lyra) on the right. Both are of the planetary nebula type, and very similar. This NASA video, based on Hubble Space Telescope ...
Albert's user avatar
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5 votes
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Can you identify the source of this image of the Pacman Nebula (NGC 281)?

It's probably going to be impossible to track the provenance of this image, but my best guess is that this is from the Nov 28, 2014 Astronomy Picture of the Day (reproduced below). I think someone ...
zephyr's user avatar
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3 votes
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What was the first nebulae of the first class?

Following the links on the Wikipedia page leads to Jones, K. G., “The search for the nebulae - VI.”, Journal of the British Astronomical Association, vol. 79, pp. 213–222, 1969., which identifies each ...
James K's user avatar
  • 125k
3 votes

Why does Helix Nebula look like an eye?

Prior to the formation of the Helix Nebula, there was a star similar to our own Sun in its post-main sequence stage. Eventually, this star consumed its entire fuel supply, which caused fusion to cease ...
4NT4R3S's user avatar
  • 1,015
3 votes
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Is it possible to detect lyman alpha blobs (LABs) with the lyman-break method?

Lyman α blobs Lyman alpha blobs (LABs) are huge (~0.1–1 million lightyears' scale) regions surrounding a galaxy or galaxy group, where we see a higher-than-average flux of Lyman alpha (or "Lyα&...
pela's user avatar
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2 votes
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Why does infrared pass through clouds of gas and dust with minimal extinction?

but why is this? My thinking is that it is because there are minimum energy transitions of infrared, causing less light to be absorbed, but when I look at the hydrogen Bohr model there are clearly ...
uhoh's user avatar
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