The Night Sky

Important Safety Information: If you cannot view the Southern Cross from your window, only go outside if you feel that it is safe to do so. Ensure to follow the current rules of your local authority for social distancing and remaining at home if you are ill. If you are unable to complete this part of the assessment, please contact the subject coordinator.

Part A: Locating South

1. Find South using the Southern Cross and Pointers. Note where this is either in the sky (South Celestial Pole, SCP) or by a landmark on the horizon. Either of two methods can be used:

a. Extend the long axis of the Southern Cross by ~4.5 times its length.

b. Extend the long axis of the Southern Cross and draw a line from the midpoint of the two Pointers at 90°. Where these lines intersect is near the SCP.

2. Find South using the compass on your phone.

3. What is the difference between these two methods in terms of accuracy, that is, can you estimate the angle difference between where South is using method 1) and method 2)? (Method for approximating angles in the night sky: the width of your little finger held at arm's length is 1-1.5° and the width of the back of your fist held at arm's length is ~10°).

4. Why is there a difference in the position of South using each method?

Part B: Stellarium

Download the Stellarium software (a free planetarium software found at: https://stellnrium.org/). Use the following steps to familiarise yourself with Stellarium:

1) On the left-hand side of the screen, click ,Location' and set it to Wollongong.

2) Underneath the ,Location' button is the ,Time/Date' button. If it is daytime, change it to be sometime at night. To speed up time in forward or reverse, either change it in the ,Time/Date' window, use the fast forward/rewind button in the toolbar at the bottom of the screen, or hold ,Ctrl' while clicking and dragging the mouse in either direction. Use your mouse wheel to zoom in and out.

3) Now that objects (stars, nebulae, galaxies, star clusters etc) in the night sky are visible, click on various objects, as well as try the different functions in the toolbar along the bottom of the screen to familiarise yourself with Stellarium. You can navigate using the mouse or arrow keys. If you are interested in learning more about the capabilities of this program, download the user guide from the Stellarium website (link above).

Use Stellarium to complete the following exercises:

1) To locate objects in the sky, astronomers use the coordinate system of right ascension/declination (see figure on page 3). Locate 10 objects, classify, and note the right ascension/declination coordinates of each in the table below. Do not use objects that are mentioned later in the assignment.

Figure 1. Right ascension and declination

2) Turn on ,Deep Sky Objects' in the horizontal toolbar. Locate the Jewel Box Cluster. Describe its approximate position in the sky in relation to other objects. Zoom in on the Jewel Box Cluster and draw it in the box below, noting the approximate position of the red supergiant.

3) Which planet(s) are visible in the night sky at sunset as of 1^st March?

4) Set the date to be 100 years in the past. Why do you think the night sky 100 years ago looks so familiar?

5) At the equator, are the North Celestial Pole (NCP) and SCP visible? Where can they be found? Hint: if you're not sure, change the location in Stellarium to the equator (either latitude 0° or find a location on the equator), and turn on the Equatorial grid (in the horizontal toolbar).

6) Set the program's time to be 7:30 pm on today's date. On the star chart below, find the following objects in Stellarium:

Circle (in RED) the following constellations:

a) Crux (Southern Cross)

b) Triangulum Australe

c) Gemini

Label (in RED) the following stars:

d) Alpha and Beta Centauri

e) Achernar

f) Sirius