Astronomy 10: Observing the Sun

Observing the Sun

Worth 30 points -- Due Monday, July 1st 2002

Again observation is integral to the scientific process. In this project you will be able to gain some understanding of the importance of observation and some of its methods.

In this project you will observe the progress of the Sun over the course of the session. You will discover what the Sun's path looks like and how it changes, and you will observe how this changes the rising and setting times and locations of the Sun throughout the year. There are two parts to this lab.

The first part will be observing the location on the horizon of the setting Sun. Choose a location where you will have an un-obstructed view of the western horizon (roof of a tall building, peak of a hill or mountain, or a large clearing). A great place would be the Lawrence Hall of Science just up the hill from campus. Wheverever you choose, be sure to always make your observations from this same location. Over the course of the session the Sun will set as seen from Berkeley between 8:23 PM and 8:36 PM. Be sure to arrive at your observing location in time to see it. You need not observe the sunset every day. Every 4-5 days will be fine. But you should be sure to keep up the observations for the entire 6-weeks of the session. Make a special effort to observe the Sun on Friday, June 21st. This is the day of the Summer Solstice.

DO NOT look directly at the Sun until it is at least three-quarters below the horizon and then it would be best to only do so while wearing a good pair of sunglasses. Looking directly at the Sun will cause extreme damage to your eyes, most of which will not be immediately noticeable.

You should record the following things:

  1. The location of the Observation
  2. Date of the Observation
  3. The precise time you observe the Sun to disappear below the horizon
  4. Weather conditions at the time and location of the observation (cloudy, foggy, clear, hazy, etc.)
  5. The Sun's position on the horizon with respect to landmarks and the compass direction (North, East, South, and West)
  6. A sketch or photograph of the sunset with landmarks clearly visible

After completing your observations write a discussion of the observations and the conclusions you can draw from them. In this discussion address the following questions:

  1. Did you observe the time and the position of the sunset to change from day to day? What causes this?
  2. Is the amount of change constant from day to day?
  3. Is the amount of change the same as seen from everywhere on Earth? Use diagrams whenever you might find them useful for explanation.
  4. Did you notice the color of the sunset to vary at all with the weather conditions? If so, how could you explain this?
  5. What was special about the Solstice on June 21st?

In the second part of this project you will see how the Sun's path in the sky changes as the session progresses. You will need to measure a shadow cast by the Sun at the same time on at least 5 different days (if you can manage it, around noon would be a good time). For best effect, 5-6 days should pass between each observation (although you can make additional observations more frequently if you wish). Your observations should span the the majority of the 6-weeks of the session. You should be sure to observe on the Summer Solstice (June 21st).

Use a vertical stick (e.g., flat-bottomed pen or pencil) to create a shadow on a flat piece of paper. Each time you observe the Sun, mark on the sheet of paper where the tip of the shadow falls. You should be careful to line up the paper exactly the same each day. Also, use the same stick each time. On at least one day, make measurements at several different, well separated times so you can trace the arc of the Sun's shadow.

After completing your series of observations, discuss the results and explain what you think is happening. You should address the following questions:

  1. At a given time of day, does the length of the Sun's shadow change from day to day? Why?
  2. At what time of day is the shadow shortest? Again, use diagrams wherever you find them helpful in explaining.
  3. How does the length of the shadow relate to the Sun's path through the sky?
  4. What was special about the shadow on the Solstice?

Using the information from both parts of this project explain why the Summer Solstice is the longest day of the year. What have you learned from this project about the Sun that you did not know before?

If the weather is foggy and you cannot make an observation at that time record that information. You should keep these observations together in a single notebook that you will hand in at the end of the project. Be as artistic as you want with the observations. A useful way to make observations would be to sketch the western horizon as seen from your observation location. Mark the compass directions on the sketch (West, Northwest, Southwest). Make several photocopies of the sketch and draw the setting sun on the photocopies at each observation.

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