The Planets

Attentive observers will be able to see Venus low in the W shortly after sunset beginning this month. As July begins, the -3.9-magntiude planet sets less than a half-hour after the Sun; by month's end, however, it stays up for 45 minutes after sunset. Telescopically, it still only shows a disk 10 arc-seconds or less in diameter.

Slightly higher up in the evening twilight, Mars creeps up on Saturn as the month progresses. On the 10th, both planets are in the same low-power telescopic field of view. Regulus, the brightest star in Leo (mag. 1.3), lurks nearby.

Jupiter reaches opposition on July 9, and so rises at sunset, attains its highest altitude at midnight, and sets at sunrise. The planet lies in Sagittarius, and glares brilliantly at magnitude -2.7. As the brightest point of light in the late night sky, Jupiter is hard to miss. (Venus, arguably its rival, is only visible briefly, in a twilit sky). Despite the fact that Jupiter remains low for Northern Hemisphere observers, this is an opposition slightly more favorable than most, and substantial detail will be visible on its 47"-wide disk. Jupiter's rotation period is only about 9 hours – and its furious spin smears atmospheric features into a global pattern of alternating dark "belts" and lighter "zones." Once every rotation the well-known "Great Red Spot" comes into view; in recent years this venerable feature has been joined by smaller spots that rival it in color and contrast (though none – so far – have exceeded it in size). Given our present ignorance about Jovian meteorology, the planet can continue to surprise us.

Jupiter’s satellite system, on the other hand, is much more predictable. Though a total of 63 moons have been discovered so far, only the 4 large one discovered by Galileo – Io, Europa, Ganymede, and Callisto – are easily visible to amateurs. These 4 are continually changing their configuration – sometimes transiting in front of Jupiter or behind it, or casting their shadows on the giant planet or being eclipsed by it. You will have months to enjoy the nightly show!

Neptune lies less than 2-l/2° to the N of Gamma Capricorni. Binoculars or a small telescope will show the 7.9-magnitude planet. A large telescope may reveal its blue-white 2.3"-wide disk.

Uranus lies below the "Circlet" of Pisces; if you visualize a line from Theta Piscium (the northernmost star of the asterism) to Kappa (the southernmost) and extend it an equal distance in the same direction, you will come to the vicinity where Uranus spends the month. Binoculars will easily show the 5.8-magnitide planet, and a telescope will show its 3.5"-diameter greenish disk.

Mercury attains greatest western elongation - 22° W of the Sun – on July 1. It then rises in the NNE almost an hour and a quarter before the Sun. It remains an easy sight in the morning twilight for the first two weeks of the month.

Dwarf Planets/Asteroids

Pluto lies just to the NW of Jupiter, in Sagittarius. At magnitude 13.9, however, it is a true challenge, demanding skill, good equipment, and superb dark skies.

The Main Belt Asteroid 3 Juno, at magnitude 10.2, can be located in the same finder field as the 6th-magnitude globular star cluster M10, near the center of the large faint constellation Ophiuchus.