1. Scaling & Daily Motion

2. How does it scale?
Properties of objects scale like the perimeter, the area or the volume
Mass scales like the volume (“more of the same stuff”)
A roof will collect rain water proportional to its surface area

3. Daily Motion

4. Daily Motion The sky seems to turn around the celestial pole
Its altitude is the latitude of the observer
The position of the celestial equator on the meridian is 90⁰ minus latitude
Objects closer to the pole have a longer daily arc, stay above horizon longer
Daily Motion

5. Daily Motion
Stars move counterclockwise around the CNP in a (siderial) day
See Stellarium or Skygazer simulations

6. Daily Motion: View changes in hours

7. The Apparent Motion of Stars at Different Latitudes
Apparent motion: motion as it appears in the sky
This is due to the position (latitude) of the observer on earth, and the fact that the earth rotates about its axis
This can also be explained by a competing theory: that there is a celestial sphere which rotates around the motionless earth.

8. These different star movement patterns made it obvious to humans early on that we live on a sphere
Change your observation spot on the spherical earth, and you will change the pattern of motion you observe

9. Mid-Northern Latitudes: Typical Rising and Setting pattern as the Celestial Sphere rotates around the CNP
North

10. The View from 35° North Latitude
Do not confuse southern stars (½ the celestial sphere, those closer to the SCP) with the stars in *your* southern part of the sky

11. Daily Rising and Setting is Different for Sun and Stars!
Due to the rotation of the Earth around its axis (YouTube) (PSU avi)
Period of rotation:
1 siderial day= 23h56m4.1s
1 solar day (Noon to Noon) =24h
Stars rotate around the North Star – Polaris
How are these rotations different?
Circumpolar – never rise or set 11