Astronomy Lab - Star Charts, North Circumpolar Constellations, Parallax, Precession

OBJECTIVES: Hold a star chart correctly to observe the stars. Define and use the terms horizon and zenith. Correctly hold and orient a star chart and use it to find stars and constellations. Locate constellations on a star chart by star hopping. Identify the zenith and the horizon on a star chart and on the sky. From a star chart, describe the direction and approximate altitude of a star. From a star chart, describe where to look on the sky for a given constellation. Practice using the fist method to locate objects on the sky. Describe the magnitude scale for brightness of stars. Locate the North Star, hence north. Set up an observing session plan for a star gazing trip. Name the five North Circumpolar Constellations and locate them on the celestial sphere. Using the celestial sphere model in lab, describe why they are always visible to Minnesotans when star gazing and why Polaris is the North Star. Look for and describe parallax in various situations. Explain Aristotle’s strongest argument against the heliocentric model. Describe precession. Measure the precession of a gyroscope. Describe how Earth’s seasons and Earth’s stars will be different in 13000 years?

BEFORE YOU COME TO LAB: Enter the title “Star Charts, North Circumpolar Constellations, Parallax, Precession” at the top of a right hand page. Enter the title and page number in your Table of Contents. On the title page, enter the date you work on this exercise. Enter the OBJECTIVES in your notebook (copy or cut and tape). Enter the word “PREPARATION”. Under it, write “horizon” and “zenith” along with a definition or description of each. Also enter the reference where you found those definitions or descriptions. Under that name the five North Circumpolar Constellations. Also, in one sentence, describe parallax (cite your reference). In one sentence, describe precession (cite your reference). How many years does it take for Earth to precess once (cite your reference)?

Under the preparation paragraph, enter “PARTNERS”. Once you begin work in lab, write the names of your partners.

BRING TO LAB: 1. Your lab notebook, prepped as described above 2. This lab write-up (printed or on laptop) 3. Pen 4. Star chart handed out in lecture (I will bring star charts for those who had astronomy during a different semester) Star Charts Page 2 of 3

PROCEDURE IN LAB – STAR CHARTS Use your star charts to answer the following questions. Write your answers in your notebook. Put the questions in your notebook too so you or someone else can tell what the answers mean. Make notes to yourself to help you understand what you did and why you answered the way you did.

Dates and Times 1. On what dates and times can you use the star chart that was handed out? Explain where you found this information.

Magnitudes Hipparchus used a magnitude scale for brightness of 1 to 6. The scale has been modified since then. 2. Name the brightest star on your star chart? About what is its magnitude? Explain why you gave your answer. 3. What is the magnitude of the faintest star on your chart? Again explain. 4. Estimate the magnitude of Polaris. Explain.

Direction and altitude 5. Where is the horizon on your star chart? Where is the zenith on your star chart? 6. How many degrees are there between the horizon and the zenith in the real sky? Explain your answer. 7. For the dates and times shown on your star chart, use altitude and direction to describe where to find Vega? Fall semester students only: Describe where to find Altair and Arcturus. Spring semester students only: Describe where to find Procyon and Capella. 8. How else could you describe the location of a star that is 80 degrees above the western horizon?

Measuring angles 9. Go to the front lobby of the science building (second floor lobby). a. Measure the altitude of the top of the Basilica from the horizon. Describe how you did this. b. Measure the horizontal angle between the MCTC sign on the T building and the American flag on the other side of Hennepin Avenue.

Holding a star chart 10. Describe how to correctly hold a star chart so that it matches the sky.

Star gazing 11. Describe how to find north using the Big Dipper. 12. Facing north, where is east? 13. Write a systematic plan for what you will do when you go star gazing to find three different constellations. What will you look for first and where in the sky will you look (use altitude and direction)? What will you look for next and where (use star hopping as well as altitude and direction)? What will you look for next and where (again use star hopping as well as altitude and direction)?

Before you leave lab 14. Staple or tape your star chart into your notebook before you leave lab.

Continued PROCEDURE IN LAB - North Circumpolar Constellations 1. Look at one of the geocentric celestial sphere models. Locate the five North Circumpolar Constellations. Star Charts Page 3 of 3 2. Can you see these from the South Pole? 3. How far north (on Earth) could you travel and still see all five all night? 4. Can you see from the model that you cannot go much further south from Minneapolis and see all five all night? 5. Describe in your own words, why Polaris does not seem to move during the night.

Continued PROCEDURE IN LAB - Parallax 1. Hold one thumb up at arm’s length. Move your head side to side. Can you see parallax compared to the wall in the background?

2. Stand at one end of the room. Look at one of the hanging cords that is closest to you. Move your head side to side. Can you see parallax compared to the distant wall? Look at a cord on the other side of the room. Compare the parallax of the two (near cord to far cord); which one shows more parallax?

3. Go into the hall. Stand at the door near the astronomy lab. Look at someone near the water fountain. Move your head side to side. Can you see parallax of that person against the background windows? Now look at someone near the stairs. Can you see parallax? Which shows more parallax?

4. Explain Aristotle’s main argument against the heliocentric model.

Continued PROCEDURE IN LAB - Precession The gyroscopes are delicate so please follow the directions and handle with care. Thanks. 1. Hold the frame of the gyroscope firmly in your hand and feed the starter T-handle through the guided end of the gyroscope. See picture below. The instructor will demonstrate if you need help. Make sure the teeth of the T-handle face the gear on the axle. Pull the T-handle away from the gyro with a strong steady pull (gyro frame is still held firmly in your hand).

2. Place the gyro on the pedestal with a slight tilt so that it precesses. Estimate the period of precession. The period of precession is the time for the axis to go around once.

3. What is the period of Earth’s precession?

4. In your own words, describe precession.

5. Due to precession, how will Earth’s stars and seasons be different in 13000 years.

Revised 13 Sep 2015