SIERRA COLLEGE OBSERVATIONAL ASTRONOMY

LABORATORY EXERCISE

NUMBER III.D. TITLE: The Sun

DATE- PRINT NAME/S AND INITIAL BELOW: GROUP

DAY-

LOCATION

PURPOSE:

· To learn how to safely view the sun with a small telescope.

· To observe sunspots and other solar features visible.

· To measure the motion of sunspots and determine the synodic period of solar

rotation.

· To calculate sidereal period given the synodic period.

· To determine the diameter of the sun by ‘pinhole projection’.

PROCEDURE:

· The instructor will demonstrate how to use the photographs in the prepared lab exercise to make measurements of the movement of sunspots between dates listed in the table below.

· Use protractor , construction compass, and straight edge as shown.

· Determine the synodic period (S) of rotation from the photographs by equation #1. Then determine the sidereal (P) period of rotation of the sun using equation #2.

· Determine the diameter of the sun with observations provided by instructor.

OBSERVATIONS, DATA, AND CONSLUSIONS:

SPOT	DATE	TIME INTERVAL ‘T’	ANGLE INTERVAL ‘D’	D/T
A	MAY 18.67	----------	----------	----------
A	MAY 20.62	1.95 DAYS
A	MAY 22.71
A	MAY 23.65
-----------	----------	----------	Spot ‘A’ Average :	Total / 3 =
B	MAY 26.66	----------	----------	----------
B	MAY 28.57
B	JUNE 1.65
----------	----------	----------	Spot ‘B’ Average :	Total / 2 =

E = 365.25 DAYS

B B

A A

	A A
B

CALCULATIONS:

DAYS

CALCULATE THE SYNODIC PERIOD VIA SPOT ‘A’

DAYS

CALCULATE THE SYNODIC PERIOD VIA SPOT ‘B’

DAYS

CALCULATE THE SIDEREAL PERIOD FOR SPOT ‘A’

DAYS

CALCULATE THE SIDEREAL PERIOD FOR SPOT ‘B’

QUESTIONS:

1. Give two possible reasons why the sidereal periods given by spot A and B are different.

2. If the period of rotation for the sun changed, how would that affect the length of an ‘earth’ day?

3. For an observer on the planet Mercury, would the synodic period of the sun be longer, shorter, or the same as that measured by an Earth observer?

4. See the diagram on the bottom front page of Sky and Telescope Reprint. Which dates for observing sunspots would provide best results (for period of solar rotation) for the method of measurement used in this exercise?

5. What ‘layer’ of the sun is a sunspot located?

6. Is a sunspot hotter, cooler, or the same temperature of the area surrounding it?

7. Calculate the diameter of the sun with the ‘pinhole projection’ data provided by the instructor. Show work below.

8. For BLUEBOOK SUMMARY - What precautions should be taken when observing the sun with the unaided eye and with an optical device?