OBSERVING PROJECT I: VISIT THE TEACHING OBSERVATORY
Deadline: April 21.
The Teaching Observatory is
located just south of the Reitz Union. Public open houses are held
every clear Friday night from 8:30pm to 10:00pm. Attend the open
house. Describe the objects you observed through the telescopes by
answering the questions on the Observing
Form. You should obtain a token from the telescope operator
to attach to this form. This project can be done anytime throughout
the semester. However, the completed form will be due by April 21,
at the very latest.
OBSERVING PROJECT II: MEASURE THE ROTATION OF THE SUN
NEW DEADLINE: March 26.
The goal of this project is to measure the rotation of the Sun using
sunspots as tracers of the spin motion. The Sun rotates
differentially, i.e., faster at the equator and more slowly at the
poles. To investigate this phenomenon, the positions of two sunspots
at different latitude on the Sun's surface will be recorded daily over
a period of at least 15 days. From these observations, you will be
able to measure the Sun's rotation following the steps given below:
1.- Get the daily SOHO image of
the Sun from the SOHO web page (Click here) . You will need at
least 15 consecutive daily images to do this project. If you miss one
day, you can always retrieve the image from the SOHO archive. Just
click on "Archive" from the main SOHO web page, and then click on
"Search for Near Real Time Images". You can select the desired start
and end dates and retrieve all the images you need for this
project. The images are called "MDI Continuum".
2.- For each image of the Sun,
draw the rotation axis (North-South diameter) and the equator
(East-West diameter). Measure the East-West diameter (d) in mm.
3.- Choose two sunspots located
left of the rotation axis and at different distances from the equator.
The sunspots can be located above or below the equator. The closer the
sunspots are to the left edge of the solar disc the better.
4.- Draw a line parallel to the
equator from the position of each sunspot. The intersection of these
lines with the rotation axis for each sunspot will be the origin of
coordinates to measure the motions of each sunspot across the solar
disc. As the days go by, each sunspot will move along the horizontal
coordinate from left to right till it disappears behind the right edge
of the solar disc.
5.- Measure the distance (s)
from each sunspot to their origin in mm. Distances to the left of
the rotation axis will have negative sign. Distances to the right of
the rotation axis will have positive sign.
6.- Draw a graph of s/d versus
t, where "t" is the time of each SOHO observation in units of days
(see example below). For instance, t=5 corresponds to 5 days after the
7.- Identify the time when each
sunspot disappears behind the right edge of the solar disc (tf). The
time it takes the sunspot to move across half the solar disc (tq), or
one quarter of the Sun's surface, is the difference between tf and the
time when s=0. The Sun's rotation period (p) is then: p = 4 * tq * 86400
(this will yield "p" in seconds).
8.- Calculate the latitude (l)
of each sunspot using the following formula: cos L = sqrt(1 - 4 *
(h/d)2). The latitude is then calculated using
cos-1 with your calculator in degree mode.
L = latitude (in deg)
h = distance from the sunspot to the equator (in mm)
d = diameter of the solar disc (in mm)
9.- Calculate the radius (r) of
the circunference described by each sunspot on the Sun's surface using
the following formula: r = Rsun * cos L (this will yield
"r" in km).
Rsun= Solar radius in km (see Chapter 9)
10.- Calculate the rotational
velocity (v) at the latitude of each sunspot using the following
formula: v = 2 * pi * r / p (this will yield "v" in km/s).
Once you have done all the calculations, the results should be
presented in three pages as illustrated in the example below. The
first page should have the fifteen SOHO images taken at different
days. Each image should be dated. The two sunspots used in your study
should be clearly identified in each image, as well as the Sun's
rotation axis and equator. The second page should show the s/d versus
t plot for the first sunspot and give the measurements and
calculations made to estimate the Sun's rotation, including "tq"
"h/d", "L", "r", and "v" (do not forget the units). Please, show the
results in the front and include all your calculations in the
back. The third page should show the same information for the second