Even a
small telescope will show you the other worlds in our solar system. You'll be
surprised by how much you'll see.
The other planets of our solar system aren’t just targets for spacecraft.
They’re also worlds you can observe. Even a small telescope will reveal details
on the giant planets. Through a medium-sized scope, you’ll see Venus, Mars,
Jupiter, and Saturn change on a nightly basis. And you won’t need a dark sky to
do so: Even under city lights, the planets provide easy objects to watch
evolve.
Observing Mercury
Through a telescope, you can detect Mercury’s phases, but details are scant.
The best times to spot this elusive orb are when Mercury lies at one of its
elongations, either farthest west of the Sun in the eastern morning sky or
farthest east of the Sun in the evening sky.
Most good views of Mercury occur at midday, when the planet sits high in the
sky. (Be careful never to point your telescope at the Sun.) If you can locate
Mercury, use a yellow or orange filter to cut down the sky’s blue light.
Observing Venus
Venus is easier to observe than Mercury. Astronomers routinely follow its
phases, along with size changes — a feature easier to spot with Venus than
Mercury. While the innermost planet looks twice as big when between Earth and
the Sun than it does when it lies on the far side of our star, Venus is more
than six times larger. Daytime observations of Venus are also easier than those
of Mercury because Venus shines brighter and can lie farther from the Sun.
Features in Venus’ atmosphere range from dusty shadings to bright spots. You
may be able to spot the most famous through a #47 (violet) filter. This filter
doesn’t allow much light through, so use it with at least an 8-inch telescope.
Look for an immense C- or Y-shaped feature centered on the planet’s equator.
Observing
Mars
Mars and Earth are closest once every 26 months, but don’t wait for the Red
Planet to reach maximum apparent size before you start observing it. As long as
Mars’ atmosphere is transparent, you’ll see detail several months before and
after opposition (when Mars rises at sunset, usually within a week of closest
approach).
Use high magnifications to observe the Red Planet, right up to the limit
of the atmosphere’s steadiness. Concentrate on a small area or a single
feature. Don’t try to observe the entire disk or dart your gaze from one
feature to another.
Mars’ atmosphere features several cloud types. Seasonal examples occur
because of heating and cooling. Discrete clouds are localized and get carried
along as the planet rotates.
Orographic clouds are made from water created by wind passing over
martian mountains and volcanoes. To view orographic clouds, use a #80A (blue)
or #47 (violet) filter. For the low-altitude ones, a #58 (green) works better.
You also can observe morning and evening clouds — bright, isolated
patches of surface fog appearing at martian sunrise and sunset. Evening clouds
are generally larger and more numerous. For the best views, use a blue or
violet filter.
Observing
Jupiter
Next to the Sun and the Moon, the celestial object with the greatest observable
detail is Jupiter. Even small scopes show several dark stripes — the North and
South Equatorial Belts — flanking the giant planet’s equator.
Watching Jupiter nightly can be rewarding. In addition to the changing
positions of its four largest moons, the planet’s rotation brings nearly all of
its possible visible area into view in a single night. Be sure to target the
Great Red Spot.
A #38A (dark blue) filter will enhance the planet’s zones. Blue filters
also sharpen bright cloud features. A #23A (red) filter brings out details
along Jupiter’s equator and sharpens contrast in the major belts.
Moving moons
Four events are possible involving Jupiter and its four large moons. An eclipse
occurs when a satellite moves through Jupiter’s shadow. An occultation occurs
when the satellite disappears behind the joivan disk.
A transit occurs when a moon moves in front of Jupiter. Best views come
when the satellites appear against the gas giant’s dark belts.
A shadow transit occurs when a moon’s shade crosses Jupiter’s disk.
Shadows appear as small black dots through any telescope.
Observing
Saturn
When observing Saturn, look for the Cassini Division, a dark gap between its
two brightest rings. Through an 8-inch scope, note the rings’ brightnesses,
color differences, and textures.
Markings on Saturn’s disk are subtle. Note any bright or dark spots
compared to the belt or zone they’re in. From night to night, these features
may change position.
Saturn’s zones appear off-white, slate-gray, or yellow. Saturn’s belts
look bluish-gray, brown, and red. Such features stand out well through red,
orange, or yellow filters. Occasional bright patches look best through a #58
(green) filter. Highlight the rings using a #56 (light green) or #82A (light
blue) filter.
Observing Uranus
Uranus’ atmosphere is usually a featureless haze. Observers first reported
details in 1870. Since then, other skywatchers have seen markings and belts.
Through a small telescope, greenish Uranus appears as a slightly elliptical
disk because of its rapid rotation. The planet moves slowly. It takes Uranus
about 44 days to move the width of the Full Moon.
Observing Neptune
To the amateur astronomer with binoculars or a telescope, Neptune is no problem
to find. At opposition, it displays a small blue disk that shines at about
magnitude 7.7.
Even a large telescope won’t reveal much detail on Neptune, although you
will see its largest moon, Triton, which shines at magnitude 13.5. The thrill
of observing Neptune comes when you first spot it through your telescope.
Because it lies farther from the Sun than Uranus, Neptune moves even more
slowly. It takes approximately 85 days for the planet to traverse a Full Moon’s
span.
Besides a telescope, it doesn’t take much to observe the planets. A good
way to start is to check out “The Sky this Month” in each issue of Astronomy.
Before you know it, you’ll have made seven new celestial friends.
Source : astronomy.com
