Download Observing the Sun Description

Physics PHY 102
General Astronomy
Observing the Sun
(based on Project Star instructions)
Description
In this lab you will construct your telescope and use it to make observations of the Sun. Hopefully the
weather will cooperate enough for the Sun to be visible for several days in a row.
Building the Telescope
For this exercise you will need to assemble a telescope from the lenses that you studied in an earlier
lab session.
MATERIALS
2 cardboard tubes (one slightly smaller than the other)
1 foam lens holder
1 1/2 inch spacer
1 plastic cap
1 cardboard washer
1 large lens
1 small lens
(NOTE: To avoid scratching the lenses, place them on a piece of paper or cloth.)
Refer to Fig. 1 for the following instructions.
Figure 1. Exploded diagram of the telescope.
1. Pick up the large lens, being careful not to smudge it with your fingers. Fit the curved side of the
lens snugly against the front of the outer tube, making sure it is positioned perpendicular to and
centered on the tube. Slip the plastic cap over this end of the tube so that the lens is firmly held in
place.
2. Using the small piece of cloth or tissue to prevent smudging, push the small lens into the foam lens
holder.
3. Slide the spacer into the foam holder such that it pushes against the flat part of the lens. Push the
spacer into the holder just far enough so the end of the spacer is flat with the end of the foam holder.
4. With the curved side of the lens facing toward the large lens, slide the foam holder into the end of
the smaller of the sliding tubes. The foam holder should be flat with the end of the tube.
Observing the Sun
Now lets use our telescope to project an image of the Sun onto a screen for observation. First, you will
want to tape a sunshade onto the telescope tube, in order to shade the area of the screen onto which the
image will be projected. To form an image of the Sun, arrange the telescope as shown in Fig. 2.
Sun
Sunshade
Viewing
Screen
Telescope
Image
Figure 2. Using your telescope to project the image of the Sun.
Light from the Sun enters the telescope, where it is focussed by lenses onto the viewing screen. The
farther the eyepiece of the telescope is from the viewing screen, the larger the image will appear.
However, increasing the magnification in this way also magnifies any motion. Thus it become more
difficult to hold the tube steady the larger the image is. Try to pick a distance that is large enough for
the image to be easily examined, but small enough so that the tube may be easily held steady. Focus
the image by sliding the eyepiece tube in and out.
Assignment
Observe the Sun on at least three days. It would be best if they were fairly consecutive – hopefully
you will be able to find 3 clear days in the next two weeks. On each day I want you to sketch the
Sun’s surface in the places provided below. Look for the following:
1. Sunspots – can you see the umbra and penumbra?
2. Limb darkening.
3. Rotation. Do the Sunspot groups appear to be moving across the surface of the Sun? Estimate
how long it takes the Sun to rotate once. This is easier if you can find consecutive clear days to
observe.
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Sketches
Sketch the Sun’s surface in the places provided below. Be sure to note the date and local time.
Date:______________________________
Time:_____________________________
Observing Location:__________________________
Date:______________________________
Time:_____________________________
Observing Location:__________________________
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Date:______________________________
Time:_____________________________
Observing Location:__________________________
Date:______________________________
Time:_____________________________
Observing Location:__________________________
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