Archived Hubble Makes 1st Precise Distance Measurement to Globular Star Cluster (nasa.gov)
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Archived Hubble Makes 1st Precise Distance Measurement to Globular Star Cluster (nasa.gov)
submitted ago by killer7
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[–] Crensch 0 points 3 points 3 points (+3|-0) ago (edited ago)
It was almost impossible until we found what's called a standard candle. That is, a way to ensure that twinkling lights out there are at a known quantity of brightness.
We found that standard candle in supernovae. They are all equally bright.
Light disperses at 1 over the distance squared, and with the knowledge of how bright something is supposed to be, and how bright it looks, you can calculate its distance from you.
Fun fact: The lack of standard candles is why Hubble's (the man, not the telescope) calculations were wrong originally, leading to a calculation that the universe was only 1.5 billion years old; younger than the planet was already known to be at the time.
Fun fact: Supernovae are the brightest things in the universe.
[–] Rakosman 0 points 1 point 1 point (+1|-0) ago
Quasars are the brightest objects in the universe, which are generated from supermassive black holes. Although, I don't know if they are in specifically visible light.
[–] Crensch 0 points 1 point 1 point (+1|-0) ago
I do believe visible light was the qualifier with that statement. It was from memory of an astrophysicist's book.
Mea culpa if I am wrong.
[–] [deleted] 0 points 1 point 1 point (+1|-0) ago
[–] Rakosman 0 points 1 point 1 point (+1|-0) ago
To measure closer objects you can use basic trigonometry to solve the distance. You look at the change of apparent angle between near and distant stars (parallax) by looking at a star from opposite sides of the Sun. Measuring the distance to certain pulsating stars (Cephids) we learned they had a reliable period based on their true brightness, and thus the periodicity of more distant stars yields the distance without the need for parallax measurements.
For distant galaxies quasars are often used, which are supermassive black holes that "emit" utterly massive amounts of radiation. You can also measure the redshift of the light, which is how much the light gets stretched by the expansion of the universe (red being the longer wavelength side of the visible light spectrum, lengthening = "toward red" = redshift)
It's worth noting that a standard candle is more about a particular star in a particular area rather than a proper unit. Various things can effect the apparent brightness.
The proper answer to your question is that there are numerous ways to measure distance. If possible and practical, more than one is used.
In this case, at least from what I can understand, they were using a continuous parallax measurement that utilized more bands of electromagnetic radiation than previous measurements to get a more precise distance.
Also, a "parsec" is the distance of something with one second (1/3600 degrees) of parallax; a parallax-second.