Science
36 watchers
Nov 2023
5:00pm, 15 Nov 2023
41,554 posts
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Nellers
Well, redshift or Aliens then
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Nov 2023
5:00pm, 15 Nov 2023
48,462 posts
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HappyG(rrr)
I thought original distance was triangulation? By taking an image from one side of earth's orbit of Sun, then other side (i.e. 1/2 year later) you have the base of a triangle. You can then calculate distance to the object by the angle (isosceles triangle). If that is bobbins, then my apols!  G
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Nov 2023
5:01pm, 15 Nov 2023
48,463 posts
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HappyG(rrr)
www2.jpl.nasa.gov
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Nov 2023
5:04pm, 15 Nov 2023
41,555 posts
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Nellers
Ooh, that might be it Happy. It just feels like the difference in position across the orbit wouldn’t be very precise wh n its the short side of a triangle that’s light years on the long sides. (Oh and the link didn’t work). |
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Nov 2023
5:19pm, 15 Nov 2023
48,464 posts
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HappyG(rrr)
Sorry, missed the l in html ! www2.jpl.nasa.gov
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Nov 2023
5:21pm, 15 Nov 2023
19,948 posts
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Cerrertonia
I think it's all of the above. Distances are measured in parsecs (parallax seconds) - carefully measure the angle to stars, know the distance the earth moved in its orbit, and then use trig to work out the distance. That gives you measurements for lots of things but is more accurate for "close" objects. Henrietta Swan Leavitt observed that for a particular kind of variable star, the cepheid, there is a strict relationship between the true brightness of the star and the period of its completely regular pulsations. And armed with that, people were able to measure how bright they appeared, how bright they really were, and therefore how far away they are - and to confirm that those measurements matched those from the parallax method. And the advantage of this method was that you can see cepheids in other galaxies. |
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Nov 2023
5:23pm, 15 Nov 2023
48,465 posts
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HappyG(rrr)
If we want to get terribly geeky, that's cos .htm is actually a valid extension so I didn't notice educba.com Interesting old person fact - when I was at Uni, probably 2nd or 3rd year, 1988/9, I remember on way into the library, seeing a notice on a notice board (remember those?!) saying something like "HyperText Markup Language", the future of documents" or something, invitation to a seminar. I don't know why it jumped out at me, but it was clearly right at the inception of the technology. G
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Nov 2023
5:27pm, 15 Nov 2023
41,556 posts
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Nellers
Ah, so you were spot on and it has nothing to do with the brightness directly, and if you know the distance from the parallax thingy then you know the ACTUAL brightness of the star because you can calculate the dimming effect of the distance. So I'd just got myself confused with thinking it was ALL about the brightness. |
Nov 2023
5:32pm, 15 Nov 2023
994 posts
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Silent Runner
Certain types of supernova provide another "standard candle". As with Cepheid variables, their behaviour - in this case I believe it's mainly the way the intensity of light from the initial explosion decays over time - is related to their absolute brightness; so given that and their relative brightness as seen from Earth, it's possible to infer their distance from us. As the useful ranges of the different methods (parallax, Cepheid variables, supernovae) overlap, they can be checked against each other to ensure consistency, and used to determine distances from "local" stars out to other galaxies. |
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Nov 2023
5:35pm, 15 Nov 2023
995 posts
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Silent Runner
In practice there are difficulties - for example, intervening gas clouds will dim the brightness of the objects being measured more than distance alone would - so it's not an easy procedure, nor always an exact one.
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