STARS AND NIGHT SKY
skies, the absence of pollution, and the deepest of dark nights make
Southern Africa excellent for Astronomy and Stargazing and there is
only one place to go: Southern Africa.
Clear skies that provide
open windows to witness the heavens: to see stars in patterns that
signify mapped constellations, and to view deep sky objects (hundreds
of thousands of objects have been discovered that lie beyond our solar
system and are known collectively as deep sky objects; this term
encompasses clusters of stars, nebulae and the galaxies).If you should
see with your mind as much as with your eyes: the astronomical vastness
of space is for the broad-minded.
There are a total of 88 official
constellations, 82 of which can be seen fully or partially from
Southern Africa; only 6 of the identified constellations are true
northern hemispheric constellations. Our observable constellations
range from the smallest (Crux, the Southern Cross) to the largest
(Hydra, the Water Snake), including one of the most recognizable,
namely Orion, The Hunter. As for deep sky objects, more than 45 are
visible in the course of an evening, year-round. Among the cited top
100 deep sky objects, we have: 40 open star clusters (e.g. the stunning
Jewel Box in Crux, and the magnificent Pleiades, commonly known as the
Seven Sisters, in Taurus), 24 globular clusters (e.g. Omega Centauri,
the largest and brightest globular cluster we know of), 15 galaxies
(e.g. Andromeda, a spiral galaxy some 2.5million light-years away), 8
planetary nebulae, 7 bright nebulae, 5 dark nebulae and 1 star cloud.
Many of these are visible to the unaided eye, and are even more
spectacular witnessed through binoculars and telescopes; and with
Sutherland’s SALT Observatory building the largest single telescope in
the southern hemisphere over the next few years, with a hexagonal
mirror array 11metres across, SALT will be able to record distant
stars, galaxies and quasars a billion times too faint to see with the
unaided eye – as faint as a candle flame at the distance of the
moon...In fact, the most famous astrophotography photos of the Milky
Way and the Southern Cross were done from South Africa.
component of our universe made up of gas and a large number (usually
more than a million) of stars held together by gravity. When
capitalized, Galaxy refers to our own Milky Way Galaxy.
A body that revolves around a larger body. For example, the moon is a satellite of the earth.
A large ball of gas that creates and emits its own radiation.
bunch of stars (ranging in number from a few to hundreds of thousands)
which are bound to each other by their mutual gravitational attraction
Violent eruptions of gas on the Sun's surface
The movement of one celestial body which is in orbit around another. It is often measured as the "orbital period."
The spin of a celestial body on its own axis. In high energy astronomy, this is often measured as the "spin period."
A star that has low surface temperature and a diameter that is large relative to the Sun.
unit of length used in astronomy which equals the distance light
travels in a year. At the rate of 300,000 kilometers per second (671
million miles per hour), 1 light-year is equivalent to 9.46053 x 1012
km, 5,880,000,000,000 miles
The path of an object that is moving around a second object or point.
can only see a few thousand stars at most with our unaided eyes. These
are a mixture of stars which are nearby, and bright stars which are
further away; but they are only a tiny fraction of the 100,000,000,000
stars in our own galaxy. We can't see stars in other galaxies without
powerful telescopes. In fact the entire brightest neighboring galaxy
(The Andromeda galaxy), which contains more stars than our own, is only
as bright as an average star visible to the unaided eye.
planets are often conspicuous and will usually draw a question from
somebody, along the lines of "What's that bright one over there?" So...
check in advance and identify which planets are going to be up, and
where they will be.
No one will notice Mercury, so you will
need to actively hunt it down and point it out. It is a tricky one and
needs to be at or near its greatest separation from the sun. You need
to catch it at the right time of twilight -- too early and the sky is
too bright to see it, too late and it's lost to the horizon. My
experience is that there is a window of about 10 to 20 minutes in which
Mercury can be seen -- but it is a worthwhile pursuit. Finding and
catching Mercury can be an adventure in itself.
Venus, and Mars make their best impression, from a stargazing point of
view, by eye -- the telescope does not add a great deal unless you are
quite serious about your astronomy. However, if Jupiter or Saturn, or
both, are visible then either will make a good showing in the telescope
-- Saturn for its rings and Jupiter for its bands and for its moons.
if you expect to have Jupiter in the sky it is also worthwhile to do a
little homework and determine where the moons will be positioned. This
varies hour by hour so you need to be precise about when you will be
showing it. We once had a moon pop out of nowhere while we were
watching -- Io was emerging from behind Jupiter (very cool).
such as Astronomy or Sky & Telescope will give you planet
positions, as well as positions of Jupiter's moons (Sky & Telescope
also shows Saturn's moons). You can also get software that will give
you this information. A good web-based Java program is available at Sky
View Cafe and an excellent, full listing of available software can be
found at nineplanets.org. Personally I use The Sky astronomy software.
luminous beauty of the night sky has a presence that is overwhelming,
and commands the attention of your tour group. This spectacular display
does all the work -- our added value to the tour group is when we
reveal to their eyes the things they otherwise would not have seen,
noticed or appreciated. So stargazing is show and tell, with emphasis
on the "show" and less on the "tell". These tours are designed to
support that approach. Some pointers:
I have found that deep
sky objects that are not visible (or barely visible) to the naked eye
and pop out in the binoculars are a particular delight. A couple of
classic examples are the Coathanger in the summer sky and the Beehive
in the Winter/Spring sky. Some other similar goodies are the Double
Cluster (winter), the Double-Double (summer), M13 (summer), and the
Andromeda galaxy (fall/winter).
Focus only on what is easily
visible. Extremely faint and challenging objects are best left for
later, when you are testing the limits of your telescope with the
hard-core crowd. Galaxies, in particular, look spectacular in
photographs and fall well short of those images in the telescope. Aside
from the Andromeda galaxy and M81, galaxies require a crystal-clear,
dark sky, or a big telescope (8 inches or larger), and preferably both.
Attach a story to each celestial feature you point out. Answer the question of why your friends care that they can see it.
the high points quickly and early, because the night chill and fatigue
of the day will get to the crowd. Even under the best circumstances you
will gradually lose more and more of your budding astronomers as the
evening wears on.
If you are going to use a telescope for any
part of your tour, it's best to have someone help by finding the next
target in the telescope for you while you are showing and explaining
other items of interest.
If you are going to direct stargazing
and point the telescope too, practice finding those objects until you
can do it quickly & easily. Practice on your own, well beforehand.
Optimally you will practice on several nights under different
conditions. If you're used to your light-polluted back yard and you get
out under a dark sky full of stars you hadn't been seeing before, that
can present a time-consuming challenge that will test the patience of
your tour group (not a good tour feature).
You don't need to
cover everything. Most stargazing sessions I lead with Scouts or
otherwise, are spur-of-the-moment affairs prompted by the abrupt
realization that we are under a perfect, clear, dark sky. As a result,
while we have covered all the items of all these tours at one time or
another, I doubt I've ever conducted a stargazing tour where I hit
every single solitary item on the list. Rather, I follow the general
flow and outline of the tours and allow the discussion to follow the
interests of the group. As you might imagine, that seems to work out
single best book to have is the Audubon Society Field Guide to the
Night Sky. I have over 40 books on astronomy and I find I keep going
back to this one. Plus it fits in your back pocket.
Also handy is Orion DeepMap 600 which can be found at www.oriontel.com.
that you want these for preparation in advance. If you plan on
referencing them while you're stargazing, bring along a red LED
flashlight, which will prevent you from destroying your night vision
once your eyes are dark-adapted.
want this for seeing so much as you want it for pointing out stars and
tracing out constellations. You therefore want one with a highly
focused beam that will give you a searchlight shaft into the night sky.
(If you can afford a green laser pointer - I can't, they're a hundred
bucks - these are much cooler and more high-tech than a flashlight.)
single most versatile instrument for astronomy is a pair of 10x50
binoculars. They're small and light so they can go on any outing, and
they're powerful. In fact, a little too powerful -- at 10x
magnification you need to control the shaking from your hands to get
the full resolving power of the image. (Some people prefer 7x50 or 8x50
for this reason.) Laying on your back, bracing the binoculars with your
hands against your face, works really well for steadying out the
shaking. You can also get a tripod mount for most binoculars.
ones (Meade, Celestron, Orion, Bushnell) will go for around $50,
excellent ones will go for as much as ten times that (or more of
course). Avoid the cheap ones (think of how much you can see through
those magnifying glasses from cereal boxes).
if you really think you need it. For stargazing purposes you won't use
it extensively, although it can add a nice touch. Decent ones start at
around $150, and the prices for good ones quickly skyrocket from there
-- from $400 to $1000 for a nice and reasonably mobile instrument. The
diameter of the objective lens, which is the most important dimension
of a telescope, needs to be greater than 3 inches for the telescope to
do much good.
The telescope I use is a Meade ETX (the
original, with a 3.5" objective). For more challenging targets (and
more impressive telescope images) we rely on one of the dads who
occasionally brings along an 10-inch scope.
The tours are just
fine without a telescope at all. I include the telescope objects in
case you have access to one and you really want to use it. If you don't
use it, no one will miss it. In fact, even though I usually have
binoculars handy for stargazing (and personally I really like them), I
have found that the tours are just fine with no optical aids at all.
We're stargazing, here, after all.