AST 1002 Module 7
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University of Florida *
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1002
Subject
Astronomy
Date
Feb 20, 2024
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docx
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Uploaded by taitai97
Project #2: Charting Sunspots
The Sun has spots! They were first observed by Galileo, and we understand them today as the
result of intense magnetic "activity" on the Sun's surface (see Chapter 11 in your text). The spots
are darker than the rest of the solar "surface" because the strong magnetic field running through
the spots inhibits the convection (up-welling) of hot gas from below. Thus, the gas in the spots is
cooler and darker than the surroundings. Above the spots (higher up in the Sun's atmosphere) is
very hot gas, which is often involved in coronal "loops" and "flares."
NASA has a satellite called SOHO (SOlar and Heliospheric Observatory) that takes daily
pictures of the Sun. Here are some images from Oct 21
st
, 2013:
The middle image above shows a few dark spots in visible light. The first image (taken at about
the same time) shows extreme hot gas measured in far-UV light. Notice that the hot spots seen in
UV light lie directly above the cool dark sunspots seen in the visible. The third image shows the
strength of the magnetic field in the solar photosphere, with black and white indicating polarity.
You can see how the sunspots align with the north and south polarities in the magnetic field. This
is the reason why sunspots always appear to be in pairs.
The Assignment:
Estimate the rotation period of the Sun based on the movement of the spots.
Procedure:
1.
Log onto the SOHO web site
2.
Go to the sunspot archive to download images of the Sun: https://sohowww.nascom.nasa.gov/data/synoptic/sunspots_earth/
There are images of the Sun in the archive since 2006. However, the Sun doesn’t always have sunspots: a good recent period for sunspots was during August and September 2017.
You can review the images from that period to select a sunspot to follow.
3.
You need to review images of different days until you find a large, clearly visible,
sunspot like the one in the image above labeled 1877, the one with the red arrow. (The
spot should be on the left side of the Sun in the first image you select because the spots
will move from left to right and you will need to track it.)
4.
Once you identify a "good" sunspot to follow, select 10 consecutive days to
download images. These images should be included with your project. Each time, record
the date listed for the image, the sunspot numbers and locations as described below.
While you're there, click on "The Sun Now" icon to see images of coronal loops and
active regions concentrated above the Sunspots. If you click around even more, you'll
find movies and other cool stuff.
5.
For your first "observation," the one with the sunspot closest to the left rim of the
Sun, record the date listed for the image, the sunspot number and mark its location on the
image below:
This grid marks every 10 degrees of longitude (and latitude), with 0 degrees longitude
corresponding to the bold vertical line down the center.
6.
Record the position of the sunspot every other day on the same grid. For
example
, if your first image was from August 21
st
, 2017, you will record the position of
the sunspot on August 21
st
, 23
rd
, 25
th
, 27
th
, 29
th
and 31
st
. That will give you 10 days of
observations.
7.
Read the approximate sunspot longitude from the grid.
Recording #1 SOHO Image 10-14-15
Recording #2 SOHO Image 10-15-15
Recording #3 SOHO Image 10-16-15
Recording #4 SOHO Image 10-17-15
Recording #5 SOHO Image 10-23-15
Recording #6 SOHO Image 10-25-15 (Sunspot 2434 is no longer visible to the eye)
Record your observations on the table below:
Sunspot Number: _______2434_________
Recording Day
Date of Observation
Sunspot Longitude
1 10-14-15
10-24-18
-60
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2 10-15-15
10-26-18
-48
3 10-16-15
10-28-18
-35
4 10-17-15
10-30-18
-31
5 10-23-15
11-01-18
58
6 10-25-15
11-03-18
No longer visible
After 10 days of observations (10 days after the first observation, not 10 observations because
you are recording the position every 2 days, not every day), estimate the rotation period of the
Sun based on the change in longitude of the spots over this time interval.
For example,
if P is the full rotation period and X is the change in longitude of a particular spot
in 10 days, then we can find the period from:
X=Longitude at day 10 – Longitude at day 1
P/10 [days] = 360/X [degrees]
X= 58 – (-60) = 118
X=118
=
=
= 3.051
10
= 3.051
P= 30.51
To be submitted electronically:
1)
The six
downloaded images used in the project (10 points).
Images should include:
a.
dates of observations (10 points)
b.
sunspot numbers (5 points)
2)
The grid you used to find the longitudes of the sunspot.
The grid needs to have:
a.
all the positions of the sunspot over the 10 day period. (20 points)
b.
An empty grid receives 0 points.
3)
The completed table you used to record the observations. (25 points)
4)
Your calculation of the Sun’s rotation period based on your 10 days observation.
a.
include all steps and show all your work (25 points)
b.
correct final answer (5 points)