2: Apparent Motion

Lab Goals

As a result of this lab, you should be able to:

• Collect observational data on the change in position of star patterns in the night sky over time
• Identify patterns relating latitude/longitude and visible star patterns.
• Identify patterns relating latitude/longitude and celestial sphere features (poles, equator, circumpolar regions, etc)

Equipment and Setup

This lab requires the following equipment on each table.

• Computer/Tablet with internet access

Submission Instructions

Submit a brief lab report that includes the following sections:

1. Results

2. Discussion

Background Information

We will continue our exploration of the night sky using a computer simulation. This simulation will allow us to see the effect of time on our sky maps. Open the University of Nebraska-Lincoln NAAP Rotating Sky Explorer Simulator:

• https://astro.unl.edu/naap/motion2/animations/ce_hc.html
• https://tinyurl.com/Sky-Explorer

The entire Earth has been mapped using coordinates of longitude and latitude. You use these coordinates every day, even if you are not aware of it. The GPS on phones and computer apps use these coordinates to pinpoint your position on Earth. Your position on Earth determines what objects are visible to you in the sky at a specific time. For this lab we will use our current location to make sense of our local view of the sky. Look up information about your latitude and longitude to set up the simulation.

Astronomical Coordinates are similar to Latitude and Longitude but they mark locations in the sky, not locations on Earth. We will explore the markings of this Celestial Sphere in this lab to make sense of sky maps and how they change over time.

The North Celestial Pole (NCP) and South Celestial Pole (SCP) will be marked on the simulation These locations represent the projections of the north and south geographical poles on Earth on the celestial sphere model.

The zenith is also marked, which represents the point directly above the observer's head on the sky. The zenith is at an altitude of 90 degrees from the horizon. Lastly, the ‘meridian’ represents an imaginary circle that passes through the north and south celestial poles. The meridian functions as a helpful way to think about the altitude of stars as the Earth turns.

The green circle represents the observer’s horizon. The horizon marks the visible separation between the Earth and the sky and is at an altitude of 0 degrees. The observable sky is what is visible above your horizon. Your horizon is local to you; if two people are at significantly different positions on Earth, they have different horizons. This is due to the spherical nature of the Earth and the fact that you cannot see around a curve. Horizons also may be partially blocked due to trees, buildings, mountains, clouds, etc.

Setup Instructions

1. Use an internet resource to look up the longitude and latitude of Hayward, CA, and enter it in the “Observer's Location” section in the lower left area of the Rotating Sky Explorer simulation. This will replicate the sky in our area.
2. On the “Star Controls” panel, select the pull-down menu for ‘star patterns’ and make sure all three options are checked (Big Dipper, Orion, and the Southern Cross). On the “Appearance Settings” panel, select the option for ‘show labels’.
3. On the “Appearance Settings” panel, select the box for “show the angle between the celestial equator and horizon.”
4. In the “Animation Controls” panel, click “ start animation” and adjust the animation controls as you like to observe the star patterns move over time.

Lab Instructions