Determining distance using standard candles
Standard Candles
- A standard candle is defined as:
An astronomical object which has a known luminosity due to a characteristic quality possessed by that class of object
- Examples of standard candles are:
- Cepheid variable stars
- A type of pulsating star which increases and decreases in brightness over a set time period
- This variation has a well defined relationship to the luminosity
- Type 1a supernovae
- A supernova explosion involving a white dwarf
- The luminosity at the time of the explosion is always the same
Determining distances using standard candles
- Measuring astronomical distances accurately is an extremely difficult task
- A direct distance measurement is only possible if the object is close enough to the Earth
- For more distant objects, indirect methods must be used - this is where standard candles come in useful
- If the luminosity of a source is known, then the distance can be estimated based on how bright it appears from Earth
- Astronomers measure the radiant flux intensity, of the electromagnetic radiation arriving at the Earth
- Since the luminosity is known (as the object is a standard candle), the distance can be calculated using the inverse square law of flux
- Each standard candle method can measure distances within a certain range
- Collating the data and measurements from each method allows astronomers to build up a larger picture of the scale of the universe
- This is known as the cosmic distance ladder
A combination of methods involving standard candles allows astronomers to build up a cosmic distance ladder from nearby stars to distant galaxies
