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I always wondered about these measurements. Excuse me if this is rookie astronomical information. I have read that we gauge the distance through brightness. Tha

I always wondered about these measurements. Excuse me if this is rookie astronomical information. I have read that we gauge the distance through brightness. That is we know how bright such an object should be at the source, and estimate the distance based on actual brightness at the instrument. How do we know it's not just brighter than we believe, instead of being as far away as we believe?

benjoffe 10y ago
A lot of research in astronomy is conducted to figure out how bright certain objects are, one classic example is "Cepheid variable" stars, these pulsate at a rate correlating with their brightness. You're right in that there is sometimes debate about whether the "standard candles" as they're referred to are as bright as we expect, see: https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Problems https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Problem...
gewoonkris 10y ago
I always understood the distance is measured by the amount of red shift: the further away a galaxy is, the faster it moves away from us due to the expansion of the universe. As a result, the wavelength of the light originating from this galaxy is streched moving it more to the red end of the spectrum. The amount of red shift can be used to calculate the distance of an object fairly accurately.
adrianratnapala 10y ago
Let's distinguish redshift from (the more murky notion of) distance. Astronomers usually just think in terms of redshift and might never convert into "X light years from Earth" until they write a press release. Red-shift is measured directly, because we have all kinds of ways of knowing about the spectrum expecte from various things, and we just see the expected pattern shifted. The calibrarion from red-shift to distance is done by considering the brightness of objects. But here astronomers can just pick and choose those objects for which they have good models. An example is the type 1a supernova (https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Supernovae https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Superno...). These are stars that were actually growing until the tripped over a very specific mass threshold and went nova. Because they all had the same initial mass, they all have the same brightness.

benjoffe 10y ago

A lot of research in astronomy is conducted to figure out how bright certain objects are, one classic example is "Cepheid variable" stars, these pulsate at a rate correlating with their brightness. You're right in that there is sometimes debate about whether the "standard candles" as they're referred to are as bright as we expect, see: https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Problems https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Problem...

gewoonkris 10y ago

I always understood the distance is measured by the amount of red shift: the further away a galaxy is, the faster it moves away from us due to the expansion of the universe. As a result, the wavelength of the light originating from this galaxy is streched moving it more to the red end of the spectrum. The amount of red shift can be used to calculate the distance of an object fairly accurately.

adrianratnapala 10y ago

Let's distinguish redshift from (the more murky notion of) distance. Astronomers usually just think in terms of redshift and might never convert into "X light years from Earth" until they write a press release. Red-shift is measured directly, because we have all kinds of ways of knowing about the spectrum expecte from various things, and we just see the expected pattern shifted. The calibrarion from red-shift to distance is done by considering the brightness of objects. But here astronomers can just pick and choose those objects for which they have good models. An example is the type 1a supernova (https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Supernovae https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Superno...). These are stars that were actually growing until the tripped over a very specific mass threshold and went nova. Because they all had the same initial mass, they all have the same brightness.