DISTANCES TO NEARBY STARS
AND THEIR MOTIONS:
An Introductory Astronomy Lab
Java Visualization Page
This demonstration allows you to explore the geometry of stellar parallaxes
and proper motions by allowing you to 'look down' (or around!) a simulated
model of the orbiting Earth, a nearby star, and a field of distant stars.
You are able to adjust many of the system parameters, such as the
distance to the star, the size of the Earth's orbit, and the speed of the
System requirements: This portion requires a Java 1.1 enabled browser,
such as Microsoft's Internet Explorer 4.0 and above. Netscape does not
yet support the latest version of the Java language and will therefore be
unable to run this package.
Instructions of use
Once the applet stops loading, you should see an edge-on view of the
Earth's orbit (which will initially look a horizontal line) surrounded by
a square box.
The circle represents the orbit of the Earth, with the sun in the middle.
The dots on the opposite side represent a field of distant stars
The straight line connects the Earth to the foreground star and continues
until it pierces the star field
The wiggly line represents the apparent motion of the star as seen by an
observer on the Earth.
The box represents....nothing, really.
- To Start/Stop the Animation
- Click on the 'Start' button to animate the Earth's orbital motion; its
label will change to 'Stop'. Click on it again to stop/pause the animation.
- To change the viewing angle / orbit orientation
- Hold down the left mouse button while moving it around the screen (drag);
let go once the orientation is to your liking. Click on the 'Change
button to adjust the orientation of the Earth's orbit; click on the same
button (now labeled 'Change View Angle') to go back to adjust viewing
- To draw a line between Earth and star
- Click on the 'Laser On' button to draw a line connecting the Earth to
the star as well as the projected path of the star onto the distant star
field. Click on 'Laser Off' to turn off this feature; the image of the
star will now be displayed on the distant star field.
- To change the distance to the star
- Click on the arrows next to the 'Distance' label.
- To change the size of the Earth's orbit
- Click on the arrows next to the 'Orbit Size' label.
- To change the star's transverse speed (proper motion)
- Click on 'Proper Motion On' to start the star's motion; click on
'Proper Motion Off' to halt the star.
What to do
We want you to play with the demo by changing the parameters, and notice
what effect they have on the observed position of the foreground star.
Specifically, answer the following:
- How is the observed parallax affected by...
- the distance to the star?
- the size of the Earth's orbit?
- the inclination of its orbit with respect to the location of the star?
- the star's own motion?
- Sketch at least 5 different 'parallax patterns' that you
were able to generate.