Celestial Sphere And Star Charts (Page 2 of 6) in pdf

Astronomy 101

Celestial Sphere and Star Charts

The Horizon is a great circle that divides the celestial sphere into two halves. The stars on one half are (in

principle) visible to a person whose location is centered at the top of the sphere for a given orientation, and

the stars in the other half are below the horizon and cannot be seen. The Meridian is a great circle

perpendicular to the horizon. It passes through the celestial poles and the zenith (the point directly overhead

of an observer on Earth).

EXERCISES:

I. Using the Celestial Sphere Model

Move the Sun and locate the ecliptic, the path the Sun takes in the sky against the background

stars over the course of a year. What are the units of measurement along the ecliptic?

______________________

Notice that the ecliptic makes an angle of 23.5 degrees with the celestial equator. This is the angle the

Earth's spin axis makes with the plane of its orbit. What constellation is the Sun in on July 5th?

______________________

In what constellation do you find the vernal equinox (the location on the sphere where the Sun crosses the

celestial equator moving northward).

_______________________

2. Longitudinal positions are given in right ascension, R.A., as measured eastward, in hours, from the

vernal equinox. The celestial latitude is called declination and is measured in degrees north or south of the

celestial equator. What are the major divisions(tic marks) of R.A. and Dec. on your globe?

R.A.__________ Dec.____________

Find the R.A. and declination of the Sun on today's date, and on the first day of spring. Notice that

declinations south of the celestial equator are negative.

Today:

R.A. ___________

Dec.__________

First day of spring:

R.A. ___________

Dec.__________

3. What stars have the following coordinates? (Note: On these globes CONSTELLATION names are in

capital letters, star names are not capitalized.)

a. R.A. 05h 54m, Dec. +07 __________________

b. R.A. 06h 44m, Dec. –16 __________________

c. R.A. 14h 14m, Dec. +19 __________________

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