13
The Planets
The planets don’t stay put like the stars, so to find
them
you
should
refer
to
our
website
(www.bintel.com.au/newsletter.html), or to charts
published monthly in our newslettrer Night Sky or
astronomy magazines like Sky and Space, Sky &
Telescope.. Venus, Mars, Jupiter, and Saturn are the
brightest objects in the sky after the Sun and the
Moon.
Your Bintel Dobsonian is capable of showing you
these planets in some detail. Other planets may be
visible but will likely appear star like. Because
planets are quite small in apparent size, optional
higher power eye-pieces are recommended and
often needed for detailed observations. Not all the
planets are generally visible at anyone time.
JUPITER
The largest planet, Jupiter, is a great
subject for observation. You can see the disk of the
giant planet and watch the ever-changing positions
of its four largest moons -Io, Callisto, Europa, and
Ganymede. Higher power eyepieces should bring out
the cloud bands on the planet’s disk.
SATURN
The ringed planet is a breathtaking sight
when it is well positioned. The tilt angle of the rings
varies over a period of many years; sometimes they
are seen edge-on, while at other times they are
broadside and look like giant “ears” on each side of
Saturn’s disk. A steady atmosphere (good see- ing)
is necessary for a good view. You will probably see a
bright “star” close by, which is Saturn’s brightest
moon, Titan.
VENUS
At its brightest, Venus is the most luminous
object in the sky, excluding the Sun and the Moon.
It is so bright that sometimes it is visible to the
naked eye during full daylight! Ironically, Venus
appears as a thin crescent, not a full disk, when at
its peak brightness. Because it is so close to the
Sun, it never wanders too far from the morning or
evening horizon. No surface markings can be seen
on Venus, which is always shrouded in dense clouds.
MARS
The Red Planet makes its closest approach to
Earth every two years. During close approaches
you’ll see a red disk, and may be able to see the
polar ice cap. To see surface detail on Mars, you will
need a high power eyepiece and very steady air!
The Stars
Stars will appear like twinkling points of light. Even
powerful telescopes cannot magnify stars to appear
as more than a point of light! You can, however,
enjoy the different colors of the stars and locate
many pretty double and multiple stars. The famous
“Alpha Cenaturi” in the constellation Centaurus and
the gorgeous two-color double star Albireo in Cygnus
are favorites. Defocusing a star slightly can help
bring out its color.
Deep-Sky Objects
Under dark skies, you can observe a wealth of
fascinating deep-sky objects, including gaseous neb-
ulas, open and Globular star clusters, and a varie-
ty of different types of galaxies. Most deep-sky ob-
jects are very faint, so it is important that you find
an observing site well away from light pollution.
Take plenty of time to let your eyes adjust to the
darkness. Do not expect these subjects to appear
like the photographs you see in books and mag-
azines; most will look like dim gray smudges.
How to Find Deep-sky Objects:
Starhopping
Starhopping, as it is called by astronomers, is
perhaps the simplest way to hunt down objects to
view in the night sky. It entails first pointing the tel-
escope at a star close to the object you wish to ob-
serve, and then progressing to other stars closer and
closer to the object until it is in the field of view of
the eyepiece. It is a very intuitive technique that has
been employed for hundreds of years by profes-
sional and amateur astronomers alike. Keep in mind,
as with any new task, that starhopping may seem
challenging at first, but will become easier over time
and with practice.
To starhop, only a minimal amount of additional
equipment is necessary. A star chart or atlas that
shows stars to at least magnitude 5 is required.
Select one that shows the positions of many deep-
sky objects, so you will have a lot of options to
choose from. If you do not know the positions of the
constellations in the night sky, you will need to get a
planisphere to identify them. Start by choosing
bright objects to view. The brightness of an object is
measured by its visual magnitude; the brighter an
object, the lower its magnitude. Choose an object
with a visual magnitude of 9 or lower. Many
beginners start with the Messier objects, which
represent some of the best and brightest deep-sky
objects, first catalogued about 200 years ago by the
French astronomer Charles Messier.
Determine in which constellation the object lies.
Now, find the constellation in the sky. If you do not
recognize the constellations on sight, consult a plani-
sphere. The planisphere gives an all-sky view and
shows which constellations are visible on a given
night at a given time. Now, look at your star chart
and find the brightest star in the constellation that is
near the object you are trying to find. Using the find-
er scope, point the telescope at this star and center
it on the crosshairs. Next, look again at the star
chart and find another suitably bright star near the
bright star currently centered in the finder. Keep
in mind that the field of view of the finder scope is
approximately 5°, so you should choose another
star that is no more that 5° from the first star, if
possible. Move the telescope slightly, until the tele-
scope is centered on the new star. Continue using
stars as guideposts in this way until you are at the
approximate position of the object you are trying to
find (Figure 17). Look in the telescope’s eyepiece,
and the object should be somewhere within the field
of view. If it’s not, sweep the telescope carefully
around the immediate vicinity until the object is
found.. If you have trouble finding the object, start
the starhop again from the brightest star near the
object you wish to view. This time, be sure the stars
indicated on the star chart are in fact the stars you
are centering in the eyepiece. Remember, the finder
scope (and main telescope eyepiece, for that matter)
gives an inverted image, so you must keep this in
mind when star-hopping from star to star.
