STANDARD CANDLES
We will now look at different examples in astronomy of measuring distance to celestial objects using knowledge of the luminosity or absolute magnitude, objects that are termed Standard Candles.
Any object that can be considered as a Standard Candle in astronomy needs to have the following properties:
- it must be easy to identify and not being confused with a different type of object
- it must have a know luminosity related to some physical property we can measure
- it should preferably be very bright so we can use it to large distances.
Fortunately there are several ways in which we can find estimates for a star’s luminosity. These methods are generally deducted from particular physical processes in a star (or entire galaxy) that are indicative for the object’s luminosity. These techniques allow us to estimate distances, even at inter-galactic scale.
But being mindful of the principle of the Distance Ladder (see page 4), we must have several objects in any particular class of standard candles to which we can also measure distance with another technique, so that we can mutually calibrate the distance scale.
Below we will describe a few of these techniques in detail and summarise several others.
We will start with a couple of methods that are based on the magnitude and the distance modulus we discussed above.
These are Spectroscopic Parallax and Main Sequence Fitting.