astronomy labs

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LABORATORY 1

THE CELESTIAL SPHERE

Equipment Star chart, skyviewcafe.com

Purpose The purpose of the lab is to understand the motion and position of the stars, Sun, and planets using the celestial globe. Introduction

From the earliest times, we have studied the stars. In our minds we have created models of how the universe worked. We created patterns out the motion and locations of the stars, Sun, and planets. The apparent patterns we have created in location of the stars are called constellations. Throughout time, we have mapped the constellations in star charts. From these star charts, we can plot the motion of the stars, Sun, and planets. The stars have three motions; diurnal (daily) motion, annual motion, and precession. The daily motion is due the Earth rotating on its axis. The annual motion is due to the Earth orbiting the Sun. And precession is caused by the Earth wobbling on its axis. As the Earth is tilted on its axis, the Sun’s motion in the sky is more complex than stellar motion as it rises and sets in different positions in the sky each day. The most complex motions are the planetary motions as they co-revolve around the Sun along with the Earth.

We can use a celestial globe to explore the sky. The globe is a smaller translucent globe with stars printed on the sky along with the lines of right ascension and parallels of declination; the coordinates of longitude and latitude in the celestial sphere, respectively. We can move the sphere to simulate the motion of the stars in the sky throughout the night and the year to explore diurnal and annual motion. Also, we can adjust the tilt of the globe to visit different locations on the Earth as to observe how the sky appears at these locations. In this lab, we will use the aforementioned two special tools in astronomy. We will visit the planetarium and confirm the results with the celestial sphere in the laboratory. We will observe the motion of the different motions of the stars, planets, and the Sun in the planetarium. Following up in the laboratory, then we will recreate the motions on the celestial globe.

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Procedure 1: Locating Objects on the Globe

1. Open skyview.com on your browser. Figure 1 shows the entry page. Note how to

change the date/times and locations on the earth. Note 12 noon is local noon and the Sun rises on eastern horizon and sets on western horizon.

Figure 1 Skyview Cafe Webpage. You can click on any star to see the altitude/azimuth and right ascension/declination.

2. Now find the objects or coordinates indicated in Table 1 and list their right ascension/declination or their names in Table 1 using your star chart or the website.

3. Now note the presences of a wave-like line surrounding the equator; this is the ecliptic, the Sun’s path around the sky during the year. Now click Celestial and Ecliptic Grid to guide you which constellation the Sun is located on the dates listed in Table 1. Record these constellations in Table 1.

Procedure 2: The Sun’s Motion and the Visibility of Stars

1. Now we are going to set the globe for our location on the Earth. We need to set the correct inclination for our sky view. We do this by determining the co-latitude. We do this set the correct altitude of the North Star. Please find our location by setting either 26◦ North or finding Davie in the location box. And set the dates for 2020 in the dates/time box as indicated in Figure 1.

2. Using the date/time box, set the sun to June 21. Now click on the hour in the date/time

box and then use the up and down arrows move the Sun from sunrise to sunset; count the number of hours from sunrise to sunset and record in Table 2. Also record the

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azimuth at sunrise and sunset for each date by clicking on the Sun. Repeat for the December 21.

3. Now set the Sun for Noon by setting the time for 12:00 noon. Please find the altitude for the noon sun for June 21. Set the website for 50 degrees using the co-latitude and find the altitude for the noon sun. Do this for 90 degrees. Repeat these for December 21. Record these altitudes for the latitudes in Table 2. Set the Sun for Midnight (00:00) on these dates and record which stars that are listed in Table 1 in Table 2.

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Table 1 Procedure 1: Locating Objects on the Globe

1) Please find these four stars in these constellations and list their right ascension and declination: Constellation Star Right Ascension Declination Bootes Arcturus Gemini Castor Ursa Minor Polaris Scorpio Antares

2) Please list and find the different stars/constellation and for these right ascensions

and declinations: Right Ascension Declination Star Constellation 6 Hr 45 Min -19◦ 18 Hr 40 Min +39◦ 5 Hr 15 Min +46◦

3) What constellations in the Sun located for each date?

Date Constellation Horoscope Constellation March 21 Ares June 21 Cancer September 21 Virgo December 4 Sagittarius December 21 Sagittarius

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Table 2 Procedure 2: The Sun's Motion and the Visibility of Stars

1) What are number of hours in the day for June 21? December 21? And the azimuths of sunrise and sunset? The altitude of the noon Sun? The stars are visible at midnight? Date For 26 degrees For 50 degrees For 90 degrees June 21 Hours _____

Sunrise _____ Sunset ______ Altitude _____ Stars Visible:

Hours _____ Sunrise _____ Sunset ______ Altitude ______ Stars Visible:

Hours _____ Sunrise _____ Sunset ______ Altitude _____ Stars Visible:

December 21 Hours _____ Sunrise _____ Sunset ______ Altitude _____ Stars Visible:

Hours _____ Sunrise _____ Sunset ______ Altitude ______ Stars Visible:

Hours _____ Sunrise _____ Sunset ______ Altitude _____ Stars Visible:

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Questions:

1) Explain and analyze the possible shift of the Sun with respect to the stars.

2) Analyze the motion and position of the Sun at the different latitudes and times of the year.

3) Looking the visibility of the stars, evaluate which location would be good for an observatory.

4) Comment on which device, star chart or celestial globe, would be better to use for observing with a telescope.