16. Solar Observing
This lab involves observing the Sun using the telescopes set up for this
by your instructor and TA during the daytime observing period that will
be announced in class and by email. To complete this lab you'll be expected
to obtain sketches from observations you make of the Sun and to combine
this with information you collect from current space and ground observations
of the Sun.
THE SUN and SPACE WEATHER
The Sun is variable on almost all timescales. In this lab we'd like you
to use all of the observing resources at your disposal to describe this
variability. Many of these changes that take place on the Sun affect the
solar system and near-Earth environment. You may wish to explore some of
the links below to learn more about this and the space environment changes
we call "space weather". This lab will involve combining observations you
make from the lab telescopes specially set up by PSB (NEVER
POINTED DIRECTLY AT THE SUN WITHOUT SPECIAL FILTERS)
and from www resources (like our own Mees observatory observations and
data obtained from the solar space experiment SOHO -- Solar Heliospheric
Observatory). Your task here is first to pick a sunspot or sunspot
group. You'll need to identify this (with an NOAA--National Oceanic and
Atmospheric Administration--ID number) and count the number of spots you
see on the disk. You can then find out about the history of this spot by
looking at past observations. What is the level of X-ray energy flux reaching
the Earth, and is there any evidence of solar flares (rapid spikes in this
energy) since the spot was on the disk? Finally I'd like you to look at
the magnetic field associated with the spot. This will either come from
Mees observations or you can use the SOHO/MDI magnetograph. This will appear
as an image with dark and lighter shades against a grey background. The
lighter shades corresponds to magnetic field lines coming up through the
surface of the Sun, and the darker correspond to field lines going down
into the solar photosphere. You'll be asked to describe these fields.
WWW Data Sources
Virtually all of the useful web sites for solar data are linked to the
IfA Solar group web pages. Go to www.solar.ifa.hawaii.edu
to start this virtual tour.
Near the top of the page are three links to mosaics of recent images
from Mees Observatory on Haleakala, from several other ground-based
observatories and from three spacecraft observatories.
These are pretty useful for current data.
And on the Spacecraft observatories page, clicking on the link beneath
one of the images gets you to the source web site, where more data
are available.
For Mees data other than the most recent day or two, it works best to
go to the page
Mees Solar Observatory.
It has links to current and archived active region maps, white light images,
and vector magnetograms, among others. Each of these has a Search Archives
feature, with neat graphic calendar search methods for data before the
current month. For data from the current month but not today or yesterday,
you have to type in the date at the top of the search page.
On the main IfA solar page, notice the link to "Other Solar Data".
This page has quite a few links to other observatories and
various resources, including the SOHO
home page and the Space Environment
Center. The MDI magnetograph data, for example,
are available from SOHO,
and a graph of the GOES12 solar X-ray flux as it is measured above the Earth's
atmosphere comes from the Space Environment Center.
LAB QUESTIONS
-
Using the lab telescope and the full-aperture neutral density filter, sketch
the appearance of the disk of the Sun. Indicate the approximate E
and North directions on your sketch. Designate one spot or spot group.
How many spots are visible on the disk?
-
From the Mees website obtain the latest
NOAA active region line sketch. Identify your designated region
from this map with its 4 digit NOAA number.
-
Notice that the solar rotation axis is inclined from the north direction
in the sky. If it takes approximately 28d for the Sun to rotate, estimate
when (how many days ago) your region was coming over the Solar east limb.
-
Use the SEC data to find the GOES 12 1-8 angstrom X-ray flux for the last
day. What is the average flux (approximately)? Were there any flares during
this time and what was the peak flux during the flare?
-
Now bring up the MDI magnetogram
for today from the Spacecraft observatories page.
If you need to find one from a previous day, click on the link below
the current image and track it down on the SOHO web site.
Notice that these images have solar north rotated
to the top of the image. Can you see your sunspot on the magnetogram? Describe
the magnetic field near it. For example is the field all of one polarity?
Is it mostly flux coming up, or going down into the Sun, or is it what
we call "bipolar"?
-
Explore how the Sun has varied since your Sunspot appeared on the Sun.
Has it gotten substantially larger or smaller (See Mees or MDI data
archives). What's the largest X-ray flux spike (solar flare) since the
spot has been on the visible disk? Is it likely that this X-ray spike originated
from this spot, or were there others that could have caused this?
Don Mickey (mickey@ifa.hawaii.edu)
Last modified: April 19, 2005
http://www.ifa.hawaii.edu/users/mickey/ASTR110L_S05/solarlab.html
