The Cosmological Distance Ladder

More than Points of Light

The methods we have discussed so far do not depend on any knowledge of what a star is.  That is, the stars are simply treated as points in the sky, and the methods for measuring distance have relied on geometric or trigonometric calculations.  Our problem is we've reached a limit, (at least with for now), on how small an angle we can measure.  To reach further out into the cosmos, we must start treating stars as more than mere points of light.  We will need to know something about the properties of stars to continue outward along the distance ladder. 

The next two pages will introduce three key concepts that will allow us to start using our knowledge of stars to move us beyond the limits of stellar parallax.  These keys are:

1.  The fact that there is a relationship between how bright an object appears and how far away it is.

2.  The fact that a star's spectrum provides a wealth of information about the star including its surface temperature.

3.  The fact that a relationship exists between a star's luminosity and it's surface temperature.

Let's see how these key facts have allowed us to reach further out into the cosmos.