As the 2009 begins, Jupiter, the largest planet, is briefly juxtaposed in the evening sky with Mercury, -- the smallest. On New Year's Day, the two are about 2° apart, but they will have already begun to separate, with Jupiter sinking lower every evening and Mercury getting higher. Jupiter is the brighter of the pair, at magnitude -1.9 as compared to Mercury's -0.7. A telescope reveals Jupiter's disk as 33 arc-seconds across; Mercury's disk, on January 1st, is just 6" across and only 2/3 illuminated. Within days, Jupiter will have disappeared into the twilight glare; it goes through superior conjunction -- passing "behind" the Sun -- on the 24th. Mercury reaches its greatest eastern elongation from the Sun, 19°, on January 4, when it attains magnitude -0.6 and displays a phase 58% illuminated. It begins to lose altitude and dims from magnitude 0 on the 9th to magnitude +1.8 on the 14th. It goes through inferior conjunction -- passing between the Sun and Earth -- on the 20th. But Mercury is not content to entirely disappear from the scene; it reappears in the morning sky, and by the 31st has reached magnitude +0.6.

Venus reaches its greatest eastern elongation (47°) on January 14. It appears much higher up in the sky than Mercury did at its highest, and is incomparably brighter. Not only is Venus a larger planet than Mercury (12,100 km in diameter vs. Mercury's 4879 km across), but its surface is enshrouded with layers of brilliant-white clouds. Mercury has no significant atmosphere, and we see only the dark regolith of its surface. In fact, during January, Venus' brightness increases from magnitude -4.4 on the 1st, to -4.55 on the 14th, to an astounding -4.7 at month's end. Its globe swells from a gibbous disk 21.2 arc-seconds across and 58% illuminated on January 1st to one 29.4" across and 42% illuminated on the 31st.

Venus can serve as a good guide to the Ice Giant planets of the outer solar system. At the beginning of January, Neptune lies about 6° to the lower right of Venus, and about 2° to the right of 3rd-magnitude Delta Capricorni. You'll need at least binoculars to see the 8.0-magnitude planet; a telescope will show its 2.2"-wide dull blue disk.

Venus can also be a guide to Uranus. It passes less than one and a quarter degrees to the north of Uranus on January 22. For several days on either side of that date, however, the two planets appear in the same binocular field. At magnitude 5.9, Uranus should be easy to make out, although it takes a telescope to reveal its 3.4"-wide greenish-white disk.

Once these objects have gone down in the west, the sky remains bereft of planets until Saturn rises, around 10:30 PM as the month begins and two hours earlier at month's end. Saturn brightens a little during January -- from magnitude 1.0 to 0.8 -- but the planet nevertheless appears somewhat subdued. The reason is that the rings, which normally contribute to its gleam, are nearly edge-on to our line of sight. In fact, at the end of December they were inclined toward us by only 0.8°. This month, they have begun a temporary retreat from that extreme, but will soon resume the march to an edge-on configuration. Earth goes through such a "ring-plane crossing" twice every Saturnian year, or about once every 14-15 years. For those newer to astronomy, this year might present the first opportunity to see Saturn as it appears "without" its rings. Unfortunately, during the actual ring-plane crossing in September, Saturn will be near the Sun in the sky and may be difficult to observe. As a practical matter, January may provide the best opportunity to see the planet with its about-to-vanish rings against a dark sky.

Mars is too close to the Sun to be visible this month.

Dwarf Planets/Asteroids

Pluto is too close to the Sun to be readily observable.

The 8th-magnitude main belt asteroid/dwarf planet 1 Ceres, is in Leo, about 15° to the NNW of Saturn.

The 8th-magnitude asteroid, 4 Vesta crosses from Pisces into Cetus and is visible the first half of the night.