Focus on the planets

Mercury is found low on the western horizon about a half-hour after sunset and sets about an hour later. The bright star very near, and to the upper left of Mercury is Spica.

Venus rises about 4:00 a.m. and is well up on the eastern horizon at dawn. The sickle of Leo lies to the left of Venus with Regulus beneath, and slightly to the lower left, of the brilliant “morning star.”

Mars is high in the south at nightfall where it spends the month among the stars of Sagittarius. While Mars is well past its prominence of early summer, a number of surface features are still visible through a medium-sized telescope.

Jupiter rises about two hours after midnight in the east-northeast where it lies between the limbs of Gemini the Twins. Castor and Pollux are to Jupiter’s immediate left.

Saturn rises on the eastern horizon around midnight as September opens and about 10 p.m. at month’s end. Saturn is located among the stars of Taurus with Aldebaran, the ‘red eye’ of the Bull to the upper right. The moon occults, or passes, in front of Saturn, on the 10th of the month but it will happen well after sunrise, 9:27 a.m. to 10:27 a.m., for viewers on the East Coast.

Uranus and Neptune are in the south nestled among the stars of Capricornus the Goat during the late evening hours. The bluish disk of Neptune and the green-blue disk of Uranus are both visible through a telescope.

Pluto is in the southwest in Ophiuchus where a powerful telescope and finder’s chart will be needed to locate it.

Our celestial neighborhood

Jupiter, the fifth planet out from the sun, contains more mass than the rest of the planets put together. Its mass is 318 times that of the Earth and pressure in the planet’s core is so great that hydrogen acts as a metallic fluid. Yet, contrary to what has been written in some books, it falls far short of becoming a star, needing 75 times more mass to ignite a nuclear fire in its core. Its gravity is 2.64 times that of Earth so a 185-pound person on Earth would weigh in at over 488 pounds on Jupiter.

The most prominent feature of its totally gaseous surface is the Great Red Spot, a storm that has been raging across the face of the planet for hundreds of years. Galileo reported on the Spot, large enough to contain two Earths, in 1610. There have been numerous probes of Jupiter, starting with Pioneer 10 in 1973. Galileo sent a probe through the Jovian cloud cover in 1995 and found it was composed of sulfur compounds, water vapor, and ammonia. A great deal of Jupiter’s chemistry was learned in 1994 when comet Shoemaker-Levy 9 crashed into its surface.

Jupiter has four major moons, with the most spectacular being Io that bears a strong resemblance to a pizza pie and is dotted with volcanoes spouting molten sulfur.

September events

1 Sunrise, 5:57 a.m.; sunset, 7:13 p.m. The moon is at apogee, or furthest distance from the earth, today.

2 Full Moon, 7:44 p.m. The full moon of September is called the Fruit Moon or Dying Grass Moon.

10 The moon’s occultation of Saturn occurs during the daylight hours on the East Coast. Moon in last quarter, 3 p.m.

12 Look for the moon and Jupiter very close together on the eastern horizon during the pre-dawn hours.

15 The thin crescent moon is to the lower left of Venus at dawn. The bright star Regulus lies below.

16 The moon is at perigee, or closest approach to the earth, today. The sun enters Virgo on the ecliptic.

17 New Moon, 6:27 a.m. The Jewish year 5762 begins at sunset.

18 Mercury is very low on the southwestern horizon shortly after sunset with Spica directly above and the crescent moon to the upper right.

22 Autumnal equinox, 7:02 p.m. This is the point at which the sun crosses the celestial equator into the southern hemisphere. The sun enters the astrological sign of Libra but, astronomically, is still in Virgo.

24 Moon in first quarter, 5:30 a.m. The moon is nestled close to Mars shortly after sunset in the teapot dome of Sagittarius.

29 The moon is at apogee for the second time this month.

30 Sunrise, 6:31 a.m.; sunset, 6:18 p.m.