Naked Eye Observing Project

Note: This is a project that can be done with the naked eye under great weather and light conditions, so please assess the weather and the amount of light pollution at your location. The use of binoculars will also help, but is optional.

The Earth is constantly rotating about its axis like a top. The Earth takes about 24 hours to make one spin. Because of this rotation, different parts of the sky are constantly coming into our view while other parts are constantly leaving our view. This rotation causes the Sun, Moon, and stars to periodically show up in our sky then leave our sky. This motion is too slow to readily perceive with your naked eyes but can be obvious when looking through a telescope.

The Earth is rotating counterclockwise when viewed from the north pole. More directly, San Diego is heading eastward (at about ~800 mph). This is why "new" sky appears above the eastern horizon and the "old" sky disappears below the western horizon (like the Sun).

For this task, pick a constellation that is visible on the horizon about one hour after sunset. Remember, stars set on the western horizon, so its best to pick something on the eastern horizon. If there are not any easily recognizable constellations to the east, the souther horizon is another good place to look. In the late Summer and early Fall, two good constellations to use are Scorpius and Sagitarrius. In late Winter and early Spring, try Canis Major and Orion.

To get better idea which constellations will be up during what times, download an evening skymap from  www.skymaps.com/downloads.html and use the skymap from the current month in the Northern Hemisphere. Note that the skymaps
typically show you what the sky looks like around 8 - 9 PM at night. See your instructor if you need help on how to use an evening skymap.

Part I Procedure (Do this early in the semester!!):

1. Read the questions first before proceeding. These will help you get an idea how detailed your observations need to be.

2. Find a nice spot where you can see the constellation and a fixed point of reference. The point of reference can be anything large and stationary; telephone poles, buildings, a mountain, etc. It maybe be helpful to mark your spot with a rock, chalk, or some tape so you can be sure you are standing in the same place later.

3. Using the Motion of the Sky sheet, draw a picture of the constellation and your reference point. In your drawing, make sure you write down where you are standing, which direction you are facing (N, E, S, W or NE, NW, SE, SW) and what time.

4. Wait about an hour or two, then go back to the same exact spot you were when you drew your first picture. Draw a picture of where the constellation is now, using the same point of reference. Do not forget to write down the time of your second observation.

5. On a separate sheet of paper, draw a bigger portion of the sky (wider field of view) such that you can easily refer to it several weeks later. This time, draw an additional three constellations that are currently visible. Again, write down the time, location, and direction you are facing. You will be using this to compare with Part II.

Questions: Please answer in clear, complete sentences and use diagrams/drawings if you need to!

1. Approximate in degrees how far your chosen constellation is above the horizon and how far it has moved from its initial position. As a general rule of thumb, you can use this:

2. Based on your two observations and your answer above, at what time do you estimate the constellation set that night? How did you come up with this estimate? (Hint: How long does it take for stars to rise from the eastern horizon and set on the western horizon?)

3. Why might this motion be more obvious through a telescope?

Part II Procedure (Do this several weeks after Part I):

1. Read the questions first before proceeding. These will help you get an idea how detailed your observations need to be.

2. Simply sketch the wide region of the sky, with the same constellations you included from Part I. Note that you should make these observations from the same place and around the same time (make sure to account for Daylight Savings Time!).

Questions: Please answer in clear, complete sentences and use diagrams/drawings if you need to!

1. Compare your observations from several weeks before. Due to the Earth's motion around the Sun, all the stars in the sky, rise about four minutes earlier each day. Over several weeks, you will be able to see those four minute intervals add up to a significant displacement in the sky. Have the constellations moved closer to the eastern, or western horizon?

2. Is this what you expect? Why?

3. Why can't we see winter constellations at night in the summer time? Where are the winter constellations in the summertime?

4. What fraction of the year is the interval between your two observations (for example, 3 months is 1/4th of a year)?

5. Approximately what fraction of the sky have the constellations moved across?