Observing Sunspots
By Jim Scala
Bay Area weather generally offers fair astronomical seeing and
occasionally, good to excellent, but much of the year our superb
maritime climate produces skies with moisture aloft that degrades
nighttime seeing. However, during the day, the Sun cuts right
through this “scud,” which helps steady solar observing.
Since we’re in a sunspot maximum, it’s an excellent
time to view the ever-changing surface of our nearest star and
enjoy the convenience of daytime astronomy.
Observing sunspots doesn’t require expensive equipment; however,
like anything, you can go as far as your pocketbook will allow.
A good two-inch telescope will do just fine, and four inches is
overkill. Many sunspot groups exceed 60 arc seconds in size. Since
a two-inch telescope will resolve 2.3 arc seconds, a plethora
of sunspot detail awaits the small scope owner. For example, figure
one is a sunspot group that covered just under four arc minutes
and was visible on November 15, 1999 when Mercury’s 9 arc
second disk transited the Sun. In a two-inch scope, Mercury was
a just a round black speck, but this sunspot group was clearly
visible in a one-inch scope.
November 15, 1999 Sunspot
Group. This sunspot group was prominent when Mercury transited
and added to the viewing. This group is 200,203 km at its
longest dimension. It could easily hold 16 earth-sized planets!
CCD images taken through a 355 Maksutov using a Thousand Oaks
Type Two solar filter. Additionally two ND-1 filters were required
to reduce light intensity enough for the CCD.
Take Correct Precautions
Anyone who has ever experimented with a magnifying glass knows
that concentrated sunlight creates enough heat to start a fire.
Indeed, a telescope is really just a large magnifying glass (light
bucket) that concentrates light and heat. So, if you look at the
Sun through a telescope, you will burn out your eye before you
can turn away. Consequently, you have to observe in one of two
ways: either cut down light by a factor of about a 1,000 before
it enters the scope; or let it into the scope and then project
the Sun’s image on an appropriate viewing screen. This latter
method has drawbacks since in a compound scope, such as an SCT
or Maksutov, internal heat can cause damage to the scope.
Caution
is essential!
Variety Awaits
Here is a sampling of sunspots that have graced the surface over
the past few months and illustrates their variety and how much
they change. Each grouping usually lasts for several weeks, if
not months. They start at upper or lower (temperate) latitudes
and migrate toward the equator. The Sun rotates in about 10 days,
so if you observe every three to five days, you can watch a group
as it takes shape, then decays, and disappears.
March 11, 2000. (Left)
The longest dimension of this group is 3 arc minutes; that’s
125,381 km. It is just below naked-eye visibility. Some
keen-eyed people could probably have seen this spot. (Right) This
is the second group visible on March 11. It was 94,040 km
at its longest dimension. It was easily visible in a small
scope.
June 2, 2000. This grouping of spots (Left) was near the Sun’s
edge. It is 84,761 km at its longest dimension. Still
not large enough for naked-eye visibility. This single sunspot
(Right) was near the center of the solar disk.
A Small Scope Will Do
The following images illustrate what you can do with a small scope.
Ellis Myers, using Kodak Gold 200 film through a 70 mm (2.7")
scope equipped with a solar filter, took the general view from
Moraga on June 12, a day with misty clouds. Jim Scala, atop Mt.
Diablo, took the other images on June 10th with a 2.5-inch scope
(at f/42) using Ilford XP-2 film. The close-up was taken with
a 2× Barlow lens, giving a focal ratio of f/84! Both negatives
will stand much enlargement, illustrating what a small scope can
do with ample sunlight.
(Left) June 12, 2000. TeleVue Oracle telescope (f.l.= 560 mm)
with Thousand Oaks solar filter.
(Below Left) June 10, 2000. General view of the sunspots taken with a 64-mm solar filter reducing aperture of a 7" (178 mm) telescope with a 2540 focal length. (Below Right) The same scope equipped with a 2× Barlow giving a final focal length of 5080 mm.
Get Started Now
The June 1999 and January 2000 issues of Sky and Telescope
have superb articles on making sunspot scopes, or converting your
present scope, from readily available materials. First, purchase
a two- or three-inch objective lens from one of the many suppliers
(choose a high focal ratio) listed in S&T; then, after a couple
of trips to the hardware store and some pleasant work at the bench,
you will have a fine sunspot telescope.
For those who own a telescope, the easiest course is to purchase
a solar filter from one of the suppliers listed in S&T;
then, you can observe the Sun directly. To really cut costs, you
can purchase aluminized Mylar and make your own full-aperture
solar screen.
Universe 2000
The dawn of the
new millennium is an unbelievably exciting time for astronomy.
Giant planets have been discovered orbiting nearby Sun-like stars.
Recent spacecraft observations of Mars show conclusively that
water once flowed freely on the red planet’s surface, perhaps
giving life a chance to take hold there. And bacteria have been
found thriving deep in the crust of the Earth, suggesting that
other subsurface environments among the planets and moons of our
solar system could be comfortable habitats for living organisms.
Universe 2000, the 112th Annual Meeting of the Astronomical Society
of the Pacific, will focus on the developments taking place in
the new interdisciplinary field of astrobiology. Leading researchers
at the cutting edges of astronomy, planetary science, geology,
and biology will give keynote addresses on Saturday, July 15th
and Sunday the 16th in Pasadena, California. Four programs will
meet the varied interests of attendees:
Universe 2000 Expo; Cosmos in the Classroom Symposium; Universe
in the Classroom: A Workshop on Teaching Astronomy in Grades 3-12;
and an Astrobiology Symposium: “From Dust to Life: Surviving
the First Billion Years of the Solar System.”
The research symposium will provide interdisciplinary links between
astronomy and the other academic disciplines related to astrobiology,
at a level that is appropriate for professional researchers who
are being introduced to other fields. We anticipate an audience
that is made up of astronomers, geologists, biologists, chemists,
and other scientists representing a host of other related disciplines.
The focus of the symposium will be the formation of the solar
system and the first billion years of Earth’s history, from
the accretion of planetesimals to the first life. A variety of
perspectives will be offered on this first phase of Earth’s
evolution, i.e., what can the fields of astronomy, planetary
science, geology, oceanography, chemistry, and biology tell us
about this remarkable period? The symposium will endeavor to develop
as complete a picture as possible of our current understanding
of this unknown era, with emphasis on what information is needed
across disciplinary boundaries.
Topics covered and issues to be explored include: the chemical
and radiation environments of the early solar system; the formation
of the Earth; the biochemistry of life; the anaerobic Earth; our
earliest living ancestor (the tree of life); life in extreme environments
and bacterial survival.
The program is intended to provide a meaningful and engaging experience
for all. Everyone is encouraged to attend the public symposium,
which complements the other symposia. Four interdisciplinary panels
exploring the relationship between astronomy, the arts, and other
areas of human endeavor should be of particular interest to members’
families and guests. Field trips to the Mount Wilson Observatory,
Griffith Park Observatory, and other engaging destinations are
also being planned. The ASP Awards dinner on Saturday, July 15,
will feature Bill Nye, the Science Guy, as a guest speaker!
Join us at ASP 2000 as we kick off the next millennium of astronomy
and space exploration! More information, and a registration form
are available at www.aspsky.org.
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