The document discusses Polaris, also known as the North Star. It explains that Polaris lines up almost perfectly with the Earth's axis over the north pole, which is why it does not appear to move in the night sky as the Earth rotates. The Earth's axis slowly changes alignment over many years in a process called precession, similar to the wobble of a top.

1. Polaris
Polaris (the North Star) lines-up almost perfectly
with the Earth's axis over the north pole.
For this reason, it does not appear to move in
the night sky as the Earth rotates.

2. Polaris
Polaris (the North Star) lines-up almost perfectly
with the Earth's axis over the north pole.
For this reason, it does not appear to move in
the night sky as the Earth rotates.

3. Precession
Over many years the Earth's axis slowly
changes alignment as it rotates and revolves.
This "wobble" is called Precession (much like a
top or dreidel).

4. Star Luminosity and
Temperature

5. Hertzsprung-Russel Diagrams
Stars are classified using 2 properties:
Luminosity – Magnitude of brightness from dim
to very bright. Directly related to size.
Temperature – How hot the star is. Directly
related to colour (blue is hottest, red is coolest).

6. Hertzsprung-Russel Diagrams

7. Hertzsprung-Russel Diagrams

8. Hertzsprung-Russel Diagrams