1. University of Scouting March 24, 2012 Gary G. Smith
In the Night Sky
University of Scouting
March 24, 2012
Gary G. Smith

2. Table of Contents Observing tools (3) Find the North Star (4)
Earth Motions: Seasonal Constellations (7)
Rotation: Clock (8, 11)
Magnitudes (9, 10)
Big Dipper as Pointer (12)
Earth Orbit (13-17)
Star Colors (18)

3. Observing tools Your eyes with a dark sky
Civil twilight: sunset + 30 minutes
Nautical twilight: sunset + 60 minutes
Astronomical twilight: sunset + 90 minutes
Star maps with constellations and bright stars marked, red flashlight
Binoculars
Telescope

4. How to Find the North Star
This method only works in the Northern Hemisphere
Find the Big Dipper
From the pointer stars draw a straight line away from the open side of the dipper
The first “bright” star on this line is the North Star, also called Polaris

6. North Star Points of Interest
Not the brightest star in the night sky.
The altitude (in degrees) of the North Star above the horizon is the same number of degrees as your latitude north of the equator.
The North Star shows you true north, not the magnetic north shown by a compass.
ToC

7. Earth Motions
Rotation: Earth spins on its axis to give us day and night (one day).
Revolution: Earth revolves around the sun to give us seasons of the year and different visible constellations (~365 days).
Wobble: just as a top wobbles about its spin axis, so does the earth (~25,000 years).
Sun: pulls the solar system around the center of the galaxy (~200 million years).

8. Rotation
Sun appears to rise in the east and appears to set in the west.
Stars appear to rise in the east and appear to set in the west unless they are close to the north (celestial) pole.
Circumpolar stars appear to rotate around the north star during the night hours (you have a clock).

9. Star Magnitudes
On a clear, dark night, the best human eyes can see stars from 1st magnitude (the brightest) down to 6th magnitude (very faint). Each magnitude ~ 2.5 times brighter than next.
Beyond 6th magnitude, one needs binoculars and telescopes to see faint objects

10. Star Bright
Two values determine just how bright a star appears in our night sky:
1) how much light (energy) the star emits
2) how far away from earth the star is
Think of this analogy: a candle and spotlight held at different distances so they look the same brightness to an observer.

11. Twenty Brightest Stars and …Polaris
Data courtesy of Wikipedia

12. Stars as a Clock
Star Clock

13. Big Dipper as Pointer

14. Earth’s Orbit
Earth Orbit
Courtesy of the Office of Naval Research

15. Spring Constellations
"Courtesy of Windows to the Universe,

16. Summer Constellations
"Courtesy of Windows to the Universe,

17. Fall Constellations
"Courtesy of Windows to the Universe,

18. Winter Constellations
"Courtesy of Windows to the Universe,
ToC

19. Star Colors Stars come in different colors from red to blue-white.
The different colors indicate the surface temperatures of the stars.
Red stars have a “cool” surface, e.g degrees.
Blue-white stars have a “hot” surface, e.g degrees.

20. Pointers to Winter Constellations

21. Pointers to Fall Constellations

22. Summer Pointers
ToC

23. Some Internet Sites http://hubblesite.org/newscenter/
Google Earth has Sky and Mars options