Construction of Celestial Sphere

This assignment, which will be graded, is for you to construct your celestial sphere. We will work with the spheres in lab Tuesday, September 2 (next week!). You must have this part completed when you come into lab, or you will not be able to complete the lab. I will check each person’s sphere at the beginning of lab. If it is completed correctly you get 100%. If it is completed, but something is incorrect, there will be deductions accordingly. If it is not completed, you get a zero.

The first part of the construction is marking the stars on the celestial sphere (steps 1-5). This isn’t complicated, although it does require a little care. It will probably take you an hour or so for this part, although it shouldn’t be hard to do while you’re sitting watching television. Read all the instructions before proceeding.

Step 1

Cut out the two star charts with a pair of scissors. Cut along the outside lines only. Each star chart will look like a flower with eight black petals.

Step 2

One of the charts is labeled “South”; this is a chart of the southern sky. Place the chart of the southern sky inside one of the plastic hemispheres with the printed side facing up. You have done this correctly if you look into the hemisphere as if you are looking into a bowl and the printed side is facing you. Carefully align the chart so the ends of the ecliptic (the line that crosses each of the chart’s “petals”) touch the base of the hemisphere at two opposite ridges (the indentations that cross at 90˚ angles). Secure the chart by placing the other hemisphere over the star chart and pushing it against the first hemisphere. Make sure that the ridges of both hemispheres match.

Step 3

Tape the edges of the two hemispheres together so that they don't slide while you are marking.

Step 4

Mark the stars on the inside of the inner hemisphere with the marking pen. Also draw the lines that mark the ecliptic and some of the brighter constellations. You can use different colored pens for the ecliptic and constellation outlines if you wish. The brighter stars are indicated by the biggest symbols. (The magnitude of a star is an indicator of its brightness. A zero magnitude star is brighter than a fourth magnitude star.)

Step 5

When you have marked all the stars, separate the two hemispheres and remove the star chart. Repeat steps 2-4 with the northern star chart and the unmarked hemisphere (the outer hemisphere the first time around). Confirm that the ecliptic lines touch the base at opposite ridges. Use the hemisphere you have already marked to secure the chart in place.

Step 6

Slide the Earth onto the center of the wooden dowel rod.

Step 7

Cut the drinking straw into two pieces, each 7.5 cm long.

Step 8

Slide the two pieces of straw over each end of the dowel rod.

Step 9

With the pushpin, make a small hole through the center of both

hemispheres (where the ridges cross).

Step 10

Slide the two star hemispheres onto the dowel with the southern hemisphere of the Earth globe facing into the southern hemisphere of stars, and the northern hemisphere of the Earth globe facing into the northern hemisphere of stars.

Step 11

Rotate the two hemispheres until the points where the ecliptic touches the equator match on both hemispheres. The dimples on both hemispheres should line up. Tape the two hemispheres together in just a few places (so that it is easy to take them apart again).

Step 12

You should trim some, but not all of the plastic surrounding the hemispheres. Leave three-quarters of an inch beyond the dimples for labels.

Step 13

Put your name on each hemisphere somewhere on the flat sheet that surrounds the hemisphere.

Labeling the sphere.

1. Label the North Celestial Pole “NCP”.

2. Label the South Celestial Pole “SCP”.

3. Draw a line along the Celestial Equator.

4. Label both equinoxes and solstices. [Hint: the vernal equinox occurs near the constellation Pegasus which looks like a square(!?) on your globe.]

5. Each dimple corresponds to one hour of right ascension. Start with zero at the vernal equinox and label them with the correct hours of right ascension in the correct direction around the sphere (hint: which season follows spring…).

6. Pack it back in the bag with all the rest of the parts and bring it to lab.