Galileo Sunspots
General Description
The EJS Galileo Sunspots Model illustrates the motion and changes in
appearance of sunspots as they move across the disk of the Sun.
Galileo's observation of the changing appearance of sunspots around
1611 provided strong evidence that the spots were actually blemishes
on the surface of the Sun, an idea that conflicted with the
Aristotelean notion of the
perfections of the heavens. Through these observations Galileo was
able to determine the obliquity of the Sun (the angle between the
Sun's equator and the Ecliptic plane) as well as the rotational period
of the Sun.
The simulation shows four randomly generated sunspots, and one sunspot
that has a user-defined latitude (to allow the user to examine the
behavior of sunspots at various latitudes). All sunspots are oval in
shape. As the spots move across the Sun their appearance changes due
to foreshortening and a slight tilt as the spots approaches the limb
(or edge) of the solar disk. These effects come about because the
Sun's surface is spherical, not flat. So the sunspot changes it
orientation relative to the viewer as it moves around on the Sun's
surface.
In addition to controls that allow the user to define the latitude of
one of the sunspots, this model allows the user to set the obliquity
of a line representing the Sun's equator. The user can adjust the
obliquity of this line until the sunspots all move parallel to the
line. In this case the obliquity of the line is the actual obliquity
of the Sun. In addition, the model displays the elapsed time (in
days) so that the user can determine the rotational period of the Sun
by measuring the time required for a sunspot to complete its motion
around the Sun. (Note that the period of a sunspots motion is
latitude-dependent, as it is in the real Sun.)
Sunspots Frame
- Display Options Menu
- Show Equator Line: show a line representing the Sun's
equator. The obliquity of this line can be adjusted by the user to
match the motion of the sunspots.
- Show Ecliptic Line: show a line representing the Ecliptic (the
plane of Earth's orbit around the sun).
- Show Directions: show arrows indicating East and West
directions along the Ecliptic.
- Show Randomly Generated Sunspots: show the four randomly
generated sunspots.
- Show User-Defined Sunspot: show the sunspot with user-defined latitude.
- Visual Elements
- Orange disk: the disk of the Sun.
- Red line: the Ecliptic.
- White arrows: East and West direction arrows along the
Ecliptic.
- Blue line: line representing the Sun's equator.
- Black ovals: randomly generated sunspots.
- Blue oval: sunspot with user-defined latitude.
- Controls
- Play/pause button: start or stop the simulation.
- Step button: advance the simulation by one time step.
- Reset button: reset the simulation and generate new
sunspots.
- Time: elapsed time in days.
- Obliquity: the angle between the equator line and the
Ecliptic, in degrees.
- Latitude: the latitude (measured from the true equator
of the Sun) of the user-defined sunspot, in degrees.
Todd K. Timberlake (ttimberlake@berry.edu)