In December, a little south of west at sunset, Venus will shine
with a pure steady white light. As Venus sets and the sky darkens,
look east and youll see golden Saturn above the trees with
Jupiter much brighter and not far behind. Just before sunrise,
low in the west, reddish Mars will be above the horizon. This
planetary show improves through winter as Venus reaches greatest
elongation on January 17 and continues through spring into summer
2001 as Mars reaches opposition on June 13. Mars will dominate
the western sky at years end when Jupiter (opposition January
1, 2002) and Saturn (opposition December 3, 2001) are visible
in the eastern sky at sunset and are well placed for springtime
into visual acuity
Seeing fine planetary detail is a skill that calls for learning
some basics about observing, telescopes and your eyes and practice.
When you practice a new skill regularly, it seems to become easy
all at once. Thats because your body must build new networks
in the tissues involved; when these pathways connect, you go from
klutz to good in one step. Your eyes require
complex neural networks and blood capillaries to feed them. Its
quite complex because the retina of the eye is actually brain
tissue, but the principles the same. Once planetary observing
is learned, its like riding a bike, you dont forget.
Saturn and Jupiter
Saturn and Jupiter just passed opposition on November 19 and 28,
respectively. This year's apparitions are the best in almost 20
years since Saturn is at 17° declination and Jupiter over
20°. This places them well above the murk and
much unsteady air that often dominate our area. Almost any optical
aid will reward the observer. Standard 7×50 binoculars will
reveal Jupiters four Galilean moons and Saturns largest
moon, Titan. While Titan revolves around Saturn in 16 days, Jupiters
four Galilean moons revolve quite rapidly and they change position
from night to night. A simple, rewarding project is to simply
observe Jupiter each clear night at the same time and note the
position of Jupiter and these four moons on a calendar. In no
time, youll have a record you can compare to the charts
in Sky & Telescope or the Observers Handbook,
and identify each moon. Yet binoculars only whet your appetite,
since Jupiter and Saturn allow a small telescope to shine. A good
small telescope magnifying 30× will show disks for both
Jupiter and Saturn.
Jupiter and Saturn
A well-made three- or four-inch
telescope with a stable mount puts you ahead of the astronomers
who discovered the interesting physical characteristics of Jupiter
and Saturn. Measure the width of this image, then look at it from
a distance of 10 times that amount; and the two pictures indicate
what you can see at about 125× on these two planets in a
Jupiter clearly yields her prominent bands and if you look hard,
youll make out some detail in them. Saturn not only shows
its majestic rings and some disk shadings, but you can definitely
make out the Cassini division.
Its not quite so easy at the telescope because the image
is not always rock steady, and bounces in and out
of focus. However, if you will simply give each planet 30 minutes
every reasonably clear evening, within about three weeks youll
see more detail than you ever imagined the small telescope would
reveal; more than in the pictures. Observe regularly and youre
bound to catch an especially steady sky one evening and youll
see much more. Youll be hooked on observing planets.
Why is Saturn
special in 2000-2001?
In 1996, Saturns rings were on edge to our line of site;
and to observers they appeared like a line going through the planet.
Saturns polar axis is sufficiently inclined so that its
South Pole is now tilted toward us and the rings have opened 23°.
The opening of rings, coupled with the planets high declination,
adds up to a spectacular sight. This positioning is nicely illustrated
by the five images taken at about the same time each year. Notice
how the rings have opened to our line of sight.
From top to bottom, these images
were made in September 1996, September 1997, September 1998,
October 1999, and September 2000.
The first two are by Thierry LeGault, printed with permission.
The others are by Jim Scala.
Observing treasures await the small telescope owner who gives
Jupiter regular observing time. As your visual acuity improves,
you will see more and more detail. Besides simply noting the positions
of Jupiters moons, several interesting observations await
the consistent observer:
Transits of Jupiters moons: The shadows are seen
as black dots against the planets bright areas with a good
four-inch scope in steady seeing. Similarly, a good eight-inch
telescope reveals the moon itself against the planets darker
shaded areas. The moon is easier in a ten-inch telescope.
Eclipses of the moons: At opposition, the moons flick out
when they pass behind the disk because Jupiters shadow is
projected directly behind. As we swing by, the eclipses take on
interesting changes since we see the entire show from either side.
Watching an eclipse from a side makes spatial relations very clear.
Red spot and other atmospheric phenomena: Transits of Jupiters
famous red spot (now a pale salmon color) is easily timed with
a three- or four-inch refractor. Once you can detect the red spot,
youve developed the visual acuity to see all the other atmospheric
phenomena Jupiter shows.
These figures show a double shadow transit such as you could follow
in a good four-inch refractor on a clear evening. The satellites
were Io and Europa. The first picture, on the left, was taken
on the morning of August 12, 2000, at 05:10 pdt. The second was
taken 35 minutes later.
For a list of December occultations, transits and shadow transits,
see Sky & Telescope, December, Page 114.
Venus and Mars
Venus has just come out from behind the Sun and is now in a gibbous
phase. As winter segues into spring, Venus will dominate the western
evening sky until early April when it eventually passes in front
of the Sun and becomes a morning object and will dominate the
dawn. Although Venus is low at declination 21°, its
position will improve to only 9° in January. As Venus
moves closer its disk grows from 17" now to 23" at greatest
elongation on January 17 and reaches 59" in April when even
binoculars will show its phases.
was poorly positioned on November 12 when this image was made,
but its gibbous phase was obvious.
Mars is too low in the sky at sunrise
and its disk too small (5") to observe effectively. However,
as Saturn and Jupiter slowly move closer to the Sun, Mars will
begin to dominate the spring observing season.
Observing Jupiter and Saturn now will slowly develop and hone
your visual acuity for Venus and Mars. Begin regular observing
now and when Mars swings close you will be rewarded with fascinating
views. Who knows, you might see the canals. Have you ever wondered:
Why were they there if they werent there?