Save our skies
Be a considerate neighbor:
Reduce nighttime glare.
Shield all your outside lights downward
(or turn them off completely)
and enjoy the beautiful, starry night sky.
August 2006 Night Sky
There is a type of star, called variables, which changes brightness
over time. The brightness changes of these stars can range from
a thousandth of a magnitude to as much as twenty magnitudes over
periods of a fraction of a second to years, depending on the type
of variable star. Over thirty thousand variable stars are known,
and many thousands more are suspected to be variable. There are
a number of reasons why variable stars change their brightness.
Pulsating variables, for example, swell and shrink due to internal
forces, while an eclipsing binary will dim when it is eclipsed by
a faint companion, and then brightens when the occulting star moves
out of the way.
So, get out your binoculars and let's play some stellar hide-and-seek.
You will definitely need binoculars to observe these stars.
Z URSA MAJORIS
Z Ursa Majoris is located in the constellation Ursa Major and within
the bowl of the Big Dipper. Z UMa is easy to find, in a friendly
constellation. Its semi-regular periodicity is exciting to follow
and results from several different pulsation periods within the
star. This variable is perfect for beginning observers to locate
and monitor, and it is bright enough to be followed with small telescopes
The star changes between a magnitude of 6.4 and 9.3 over a period
of 196 days.
R CORONAE BOREALIS
R Coronae Borealis is one of the most interesting and most peculiar
of all variables. It has been a favorite with observers ever since
its discovery nearly two hundred years ago. Located inside the bright
circlet of stars that form the Northern Crown, R CrB is usually
easy to find with binoculars at sixth magnitude. R CrB type stars
stay at maximum and then intermittently experience fluctuations
because dust cloud periodically obscures the star. R CrB, when exposed,
is a star that usually shines around sixth magnitude, and it is
during this time that the star is at maximum. At highly irregular
time intervals that are unpredictable, the star enters a deep minimum
caused by a dust cloud. There are no good explanations for the why
or how dust clouds form. Eventually, the dust cloud moves out of
the way, reexposing the photosphere of the star. This star varies
between a magnitude of 5.9 and a very dim 14.4.
RY Sagittarii is located in the constellation of Sagittarius, just
a few degrees north of the boundary shared with Corona Australius.
In fact, it can be found just between the handle of the tea-kettle
asterism in Sagittarius and the crown of Corona Australius. RY Sgr
is another variable belonging to the R Coronae Borealis-class (RCB)
of stars. With just under fifty known RCB variable stars, it appears
to belong to an elite gang of rebellious variables. While astronomers
have been trained to think that activity of a star generally occurs
as the star brightens, RCB stars prefer to do just the opposite.
While spending the majority of their time at maximum brightness,
this odd lot of variable stars are seen to be in an active phase
as they fade to fainter magnitudes. RY Sgr varies between 6.0 and
13.3 magnitude irregularly because of the dust clouds it generates.
R Cyg can be found at the northwestern wing of the swan constellation
of Cygnus. Nestled between the bright stars of iota and delta Cyg,
R Cyg is relatively easy to find. R Cyg has an average magnitude
of 7.5 at maximum and 13.9 at minimum, with a mean period of 429.2
days between bright and dim.
Anyone can be a variable-star observer. All you really need to
begin observing are your eyes, a pair of binoculars, and a little
patience. For more information about variable stars and how to observe
them, see the American Association of Variable Star Observers Web
THE PLANETS AND THE MOON
• Mercury and Venus can be found side-by-side very low
in the east just before sunrise the first week of August.
• Mars this month will be very low in the west after sunset
the first half of the month.
• Jupiter is high in the sky after sunset, shining as the
brightest “star” in the sky.
• Saturn will rise with the Sun this month and will not
• Look for the full moon on August 9 and a new moon on August
If you have a question, comment, or suggestion for Charlie, e-mail
him at: firstname.lastname@example.org.