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2001–2002: A Year of Planets

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 you’ll 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 year’s 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 observing.

A digression 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. That’s 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. It’s quite complex because the retina of the eye is actually brain tissue, but the principle’s the same. Once planetary observing is learned, it’s like riding a bike, you don’t forget.

Saturn and Jupiter Now!

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 Jupiter’s four Galilean moons and Saturn’s largest moon, Titan. While Titan revolves around Saturn in 16 days, Jupiter’s 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, you’ll 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 at 125×

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 three-inch telescope.

Jupiter clearly yields her prominent bands and if you look hard, you’ll 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.

It’s 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 you’ll see more detail than you ever imagined the small telescope would reveal; more than in the pictures. Observe regularly and you’re bound to catch an especially steady sky one evening and you’ll see much more. You’ll be hooked on observing planets.

Why is Saturn special in 2000-2001?

In 1996, Saturn’s rings were on edge to our line of site; and to observers they appeared like a line going through the planet. Saturn’s 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 planet’s 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 Jupiter’s moons, several interesting observations await the consistent observer:

• Transits of Jupiter’s moons: The shadows are seen as black dots against the planet’s bright areas with a good four-inch scope in steady seeing. Similarly, a good eight-inch telescope reveals the moon itself against the planet’s 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 Jupiter’s 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 Jupiter’s 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, you’ve 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.

Venus 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.

Start Now

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 weren’t there?”

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