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Astronomy 1401 Department of Physics and Geology
Celestial Globe
Equipment Needed Quantity Equipment Needed Quantity Celestial Globe 1 Star and Planet Locator 1 Starry Night 1
Part 1: Background – Celestial Globe
1.1 General
The celestial globe (see Figure 1.1 ) is one of the oldest tools in Astronomy. In ancient times humans thought that the stars were fixed to the inner surface of a great celestial sphere that surrounded the Earth and turned daily carrying the stars around it. Modern humans realize there is no real celestial sphere and that the stars are distributed throughout space at various distances. Nevertheless, it is still convenient to imagine that the sky is a sphere of great radius with the Earth a tiny object at the center. The celestial globe is a model of this sphere.
Figure 1.
1.2 Vocabulary
North Celestial Pole and South Celestial Pole
Notice that the globe is pivoted at the North Celestial Pole “ Pn ”, and at the South Celestial Pole “ Ps ” (see Figure 1.2 ). These are points on the sky resulting from the intersection of the Earth’s rotation axis and the Celestial Sphere. These points are the extensions of Earth’s North and South Pole onto the Celestial Sphere.
Celestial Equator
Halfway between the celestial poles lies the Celestial Equator , the intersection of the plane of Earth’s equator and the Celestial Sphere (see Figure 1.2 ). As the Sun, during a year, moves eastward along the ecliptic it eventually crosses the Celestial Equator as it goes from the southern half of the sky into the northern half. This point of intersection is called the Spring Equinox; the Sun arrives there around March 21, the beginning of spring.
Perhaps it is convenient at this point for you to put the Celestial Globe in such a form that the North Celestial Pole points straight up, so you can visualize the Celestial Equator.
Figure 1.2 The North Celestial Pole (Pn), the South Celestial Pole (Ps), the Celestial Equator and the Ecliptic on the Celestial Globe
Ecliptic
The apparent path of the Sun, called the Ecliptic (see Figure 1.2 ), is inclined 23.5o^ with respect to the Celestial Equator. This inclination is the result of the tilt of the Earth’s axis, and is what causes our seasons. The Ecliptic might also be thought of as the projection of the plane of the Earth’s orbit onto the Celestial Sphere. Months and days of the year are marked off along the Ecliptic so that you can locate the position of the Sun on any day of the year. On the Celestial Globe the Ecliptic is easily found
Figure 1.3 Declination (Dec.) and Right Ascension (R.A.)
Star and Planet Locator The Star and Planet Locator is a tool used to observe the night sky for latitude 40˚N, it is also useful for any mid-latitude area of the Northern Hemisphere.
How to use:
- The outermost-movable ring (white letters/numbers on blue background) contains the days corresponding to each month of the year.
- The innermost-fixed ring (blue letters/numbers on white background) contains the time of day.
- To use the star and planet locator, align the month and day you are investigating with the time of day by rotating the outermost-movable ring.
- Once the month/day have been aligned with the time of day, a map of the corresponding “night-sky” will appear showing the positions in the sky of stars and constellations.
- Note that the ecliptic , the celestial equator , and the Milky Way band, as seen in the sky, will also be shown.
SAFETY REMINDER
Do not drop the Celestial Globes.
Follow the directions for using the equipment.
Part 2: Lab Activity – Celestial Globe
The purpose of this laboratory activity is to learn the basic terms and abbreviations used in the celestial sphere and its coordinate system. Let’s start our tour through this imaginary sphere by examining your celestial globe in front of you.
2.1 Big Dipper (in Ursa Major)
- Locate the Big Dipper (hint: it is in the constellation of Ursa Major , close to the North Celestial P ole ).
- Draw in the space provided in the lab report, section 3.1 (as best as you can), the Big Dipper , numerating the position and the name of each star belonging to it.
2.2 Declination (Dec.)
Indicate the Declination (Dec.) of the objects listed in the lab report section 3.2.
2.3 Right Ascension (R.A.)
Find the Right Ascension (R.A.) for the objects listed in the lab report section 3.3.
2.4 Problems
Solve the problems in section 3.4, using the celestial globe.
2.5 Star and Planet Locator
Solve the problems in section 3.5, using the star and planet locator.
2.6 Starry Night Program
Solve the problems in section 3.6, using the starry night program.
Record your results in the Lab Report section.
