University of Michigan - Department of Astronomy

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Daytime Observing at Angell Hall Worksheet

NEVER LOOK AT THE SUN THROUGH ANY TELESCOPE, INCLUDING THE FINDER SCOPES, UNLESS A SOLAR FILTER IS CORRECTLY ATTACHED!! Permanent eye damage can be 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 neutral-density (white light) filter and an Hα filter.

Part 1: The Sun's Photosphere

  1. The GSI will project the Sun's image onto a screen, showing the photosphere. What do you see? Describe it in words and make a sketch below.

    space for sketch

Part 2: The Sun's Chromosphere

  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? Is it safe to look through the telescope at the Sun?


  2. Note that we actually use two filters: one to reduce the light entering the telescope, and one to limit what you see to a single wavelength, the Hα nebular emission line. See the Introduction for more on this filter.

    Look through the telescope. Describe the color of the Sun when viewed with the Hα filter. Be as specific as you can in your description.


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

    space for sketch
  4. Label the features on your sketch (e.g., sunspot, prominence, etc).

Part 3: Venus

Examine the 0.4-m telescope in the dome, comparing it to the other telescopes. Compare the field of view in the finder scope and the main telescope.

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


  2. Is this telescope mounted for the altitude-azimuth, or equatorial coordinate system? How can you tell?




  3. Sketch what you see through the main telescope. If Venus does not look round, include the orientation in your sketch, with up at the top.







Concluding Questions

  1. Explain why looking at the Sun through an unfiltered telescope is far more harmful than even looking at it without a telescope.



  2. Compare and contrast your Hα and white light sketches. Why are features similar and/or different?




  3. Consider a filter with the same wavelength range as Hα but centered on a different, random wavelength. Would we see the photosphere, chromosphere, corona, or none of these? Explain.




  4. With a ruler, measure one of the sunspots in your white light picture. Indicate the spot in your sketch. Given that the Sun's apparent diameter on the sky is about 32 arcminutes, set up a proportionality to obtain the angular diameter of the sunspot. Solve and show your work.





  5. The actual diameter of the Sun is 1.4x106 km. Use the answer to the previous question to determine the diameter of the sunspot in km. Show your work. How does this compare to the diameter of the Earth (12,400 km)?






updated: 7/9/10 by MSO and SAM

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