1. Hubbles Law

2. Lesson Objectives
To understand the relation between distance to, and radial velocity of, a galaxy.
To perform simple calculations using the Hubble Law equation.
To show an understanding that the Hubble Constant can be used to determine the age of the Universe.

3. What is Hubbles Law
So far we have looked at evidence for the expanding Universe. Not until the early 20th century did scientists realise that 'spiral nebula' were actually different galaxies and not part of ours. One of the most prominent of modern astronomers was Edwin Hubble.
He proposed there was a relationship between the distance to galaxies to their redshift (or receding velocity). In other words how fast a galaxy moved was in proportion to its distance.

5. Hubble More Information
Velocity is taken by measuring the galaxy over a period of time
We can calculate the distance to nearby galaxies by knowing their apparent and absolute luminosity.
To do this Hubble needed a constant of proportionality - the Hubble constant.
This is a special measurement to astronomers, as it means they can measure the age of the Universe
Different measurements have been made, notably by the Hubble Space Telescope (HST) and Wilkinson Microwave Anisotropy Probe (WMAP). Most past measurements have been values between 50 and 100 Mpc. HST measured 74.2 ± 3.6 (km/s)/Mpc in 2009.
If the number is too high we find stars older than the Universe, and if it is too low there is not enough matter in the Universe to account for it. The constant therefore supports the Big Bang theory.
There are two areas on which scientists cannot yet agree:
1. An accurate measurement everyone can agree on
2. Knowing if the constant is constant and always has been that value.

6. Apply your Knowledge
Try Hubbles law Questions

7. Review Why is the value of the Hubble constant significant?
In a sentence, describe Hubble's Law
What is the formula for Hubble's Law?