1. Navigating the Night Sky
Constellation Charts and Planispheres

2. Big Questions:
What are the “guideposts” we use when navigating the night sky?
How do Earth’s rotation and revolution affect what we see in the sky?
What tools can we use to locate objects in the sky?

3. Celestial Sphere “Guideposts”
Horizon
Zenith
Celestial North Pole
Celestial Equator
Ecliptic
Declination
Right Ascension

4. Your Personal Location
Your horizon (the red line) depends on your location
Your latitude on Earth is also the Declination of your Zenith

5. The Horizon and Visible Stars
The southernmost stars you can see must have a declination greater than – (90o - l)
For us: - (90o – 40o) = - 50o
So we can never see the “Southern Cross” constellation Crux, because it has a declination of - 60o and is always below our horizon.

6. Because of Earth’s Rotation
Celestial Sphere appears to rotate clockwise (E to W)
Stars near the equator (equatorial constellations) appear to rise in the East and set in the West
Stars near the poles (circumpolar constellations) appear to circle around the Celestial Poles

7. Because of Earth’s Revolution
Each day, you look in a slightly different direction in space
Stars appear to rise 4 minutes earlier each night. 
In two weeks, the stars rise about an hour earlier
Different stars are visible in the winter vs. the summer
In 12 months, they appear to move all the way around the sky back to the same position

8. Star Trails
Equatorial stars
Circumpolar stars

9. Measuring the Sky
Astronomers measure angular separation of objects in degrees.
1o = 60’ (arcminutes) The full Moon is about 30′ across.
1’ = 60” (arcseconds) The resolution of a good telescope
The angular separation of any point on the horizon and the zenith is 90o.

10. Angles in the Sky
Your hands and fingers are convenient measuring tools. When you hold your hand at arm’s length, you can estimate angles like this:
10o 1o 5o
15o
25o

11. Types of “Sky Maps”

12. A Sky Chart for a specific date, time, and latitude
Shows the sky visible to an observer at a specific latitude for a specific date and time. The circle’s edge is the horizon, your zenith is at the center

13. A Planisphere or Star Wheel
Adjustable
Rotate the wheel until the date matches with the time of the observation.
Polaris is at the center
Align to a cardinal point (N, S, W, E)

14. Equatorial Constellation Chart (SC001)
Shows Declinations from -60 to +60
Good for any date/time/mid-latitude

15. Web interactive
For practice reading an equatorial constellation chart, visit:

16. Circumpolar Constellation Chart (SC002)
Shows constellations near the North or South Celestial Poles
Shows lines of RA and Dec
Good for any date/time