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Parallax and standard candles
Intermediate
Methods to measure cosmic distances.
Parallax gives distances to nearby stars: d (pc) = 1/p (arcsec). Standard candles (Cepheid variables, Type Ia supernovae) with known luminosity give greater distances via the inverse-square law.
Gaia measured a billion stars.
A distance ladder links the methods.
In more detail
Parallax measures the apparent shift of nearby stars against distant background stars as Earth orbits the Sun. Standard candles, such as Cepheid variables and Type Ia supernovae, provide distances for farther objects.
Real-world uses
- Gaia measures parallaxes for billions of stars.
- Cepheids and supernovae calibrate the distance scale to galaxies.
- Astronomers use parallax for nearby stars, and standard candles such as Cepheids and supernovae for more distant galaxies.
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Frequently asked questions
What is a parsec?
The distance at which one astronomical unit subtends one arcsecond, about 3.26 light-years.
What is a standard candle?
An object with a known luminosity, which lets us compute its distance from its brightness.
What is a standard candle?
An object whose true brightness is known, so its apparent brightness reveals its distance.
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