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# Solar Observing and Angular Size

Do not look at the Sun through any telescope, including the finder 'scopes, unless there is a filter on it. Permanent eye damage can be almost instantaneous!

Some of the smaller telescopes at Angell Hall have solar filters so you can observe the Sun safely. There are two types of filters here: a white light filter and an H-α filter.

## Part 1: White Light Filter

1. Before you begin, take a look at the front of the telescope. You may need to back far away or step up onto the stepstool to see. What do you see? Why is it safe to look through the telescope at the Sun?

2. Is this telescope a reflector or refractor? How can you tell?

3. Look through the telescope. What color is the Sun viewed with the white light filter?

4. What do you see? Describe it in words and do a sketch below.

## Part 2: Hydrogen &α; Filter

Note that this actually uses 2 filters, one to cut down on the light entering the telescope and one to limit what you see to a single wavelength: the first Balmer line. See the introduction for more on this filter.

1. Is this telescope a reflector or refrator? How can you tell?
2. Look through the telescope. What color is the Sun viewed with the H-α filter?
3. What do you see? Describe it in words and do a sketch below.
4. In the sketch, Label the features in your sketch with what they are (eg. sunspot, prominence, granulation, etc).

5. Compare this sketch to the white light one. Is there a link between activity on the photosphere and in the chromosphere?

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## Concluding Questions

1. Measure one of the sunspots in your white light picture. Indicate the spot in your sketch. Given that the Sun is about 32 arc minutes across, what is the angular size of the sunspot?

2. The actual diameter of the Sun is 1.39x106 km. Use this and the answer to the previous question to determine the diameter of the sunspot in km. Show your work. How does this compare to the size of the Earth (12,400 km diameter)?

3. Compare the H-α to the white light sketch. Is there a link between activity on the photosphere and in the chromosphere?

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Updated: 7/9/10 by SAM

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