On a clear dark night in Maine with no interference from the moon, the sky appears dotted with millions of stars. One reader was curious: Just how many stars can we see? There is no true answer to this question as each person’s eyes are different even if sky conditions are ideal.

A website called Universe Today says the number would be about 9,000 with the naked eye, 200,000 with strong binoculars and 15 million using a backyard telescope. These numbers seem huge, but the Milky Way is estimated to contain 100 to 400 billion stars. What we see is an extremely small fraction of what our galaxy contains.

The visible universe is estimated to contain a septillion stars or 1 followed by 24 zeros! A book worth reading by late astronomer Carl Sagan, “Billions & Billions: Thoughts on Life and Death at the Brink of the Millennium,” offers insights on this mind-boggling topic.

Focus on the planets

Mercury just peeks above the western horizon a half hour after sunset. It will be hard to spot even with binoculars and the best chance of seeing it is on Sept. 24 when it is just above the bright star Spica.

Venus is about a third of the way up on the west-southwest horizon a half-hour after sunset. Venus brightens as the month wears on, and viewers will be treated to a pairing with the thin crescent moon Sept. 8.

Mars rises in the east around 4:00 a.m. and while small and faint, can be distinguished by its reddish hue with optical aid. Check out Mars Sept. 8 and 9 as it passes through the Beehive Cluster.

Jupiter may be found high in the east shortly after midnight as the month opens and rises earlier each successive night. Viewers with telescopes are treated to the dance of its four moons around the giant planet.

Saturn starts the month to the upper left of Venus but closes rapidly with its brighter neighbor culminating in a near pairing Sept. 18. Saturn is too low to the horizon for good viewing and sets 2.5 hours after the sun as September opens and earlier each night as the month progresses.

Uranus is in the east among the stars of Pisces after midnight, while Neptune occupies Aquarius in the south. Both the blue-green disk of Uranus and the blue-gray disk of Neptune may be found with the aid of a finder chart published by Sky & Telescope magazine on-line at skypub.com/urnep.

September events

1 Sunrise, 5:57 a.m.; sunset, 7:13 p.m. Jupiter stands directly above the crescent moon on the eastern horizon about an hour before sunrise. Mars is far to the lower left of the moon.

2 Mars is to the upper left of the moon when looking east at dawn. This is a good chance to see the faint planet.

5 New moon, 7:35 a.m.

8 Looking west about an hour after sunset reveals Spica, Venus with the moon adjacent, and Saturn in an ascending diagonal line from the horizon. Mars is less than half a degree from the center of the Beehive Cluster.

11 Orange Antares of Scorpius is situated directly below the moon tonight.

12 Moon in first quarter, 1:09 p.m.

15 Moon at perigee or closest approach to Earth today.

16 Saturn lies directly above Venus in the west-southwest an hour after sunset. The sun enters Virgo on the ecliptic.

19 Full moon, 7:12 a.m. The full moon of September is the Harvest Moon as it occurs closest to the fall equinox. Rarely the Harvest Moon falls in early October. Other names for the September full moon is the Corn Moon, Fruit Moon, or perhaps for rabid fans, the Football Moon!

22 The fall or autumn equinox occurs at 4:44 p.m. This is the point at which the sun crosses the equator into the southern hemisphere. The sun enters the astrological sign of Libra at the equinox but, astronomically, is still in Virgo.

24 Saturn is just to the right of Venus in the west-southwest a half hour after sunset with Mercury just above the horizon far to the pair’s lower right.

25 Mercury is less than a degree from the star Spica in the evening sky. This is the closest approach of a planet to a 1st magnitude star this year.

27 Moon in last quarter, 11:55 p.m. The moon is at apogee or farthest distance from the Earth today.

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

Send astronomical queries to Clair Wood at cgmewood@aol.com or care of the Bangor Daily News, Style Desk, P.O. Box 1329, Bangor 04402.