The moon’s orbit is tilted by about five degrees. When the orbit crosses the ecliptic, the imaginary plane where the planets orbit the sun, it’s termed a “node.” So, on Sept. 7, at 11:08 p.m. UT (5:08 p.m. CST), the moon is at the ascending node. Ascending meaning moving from south to north, descending goes the other way.
A node-crossing event brings about an eclipse season twice a year, sometimes three times a year. Thus, on Sept. 7, the sun, Earth and the full moon line up such that Earth’s shadow darkens the moon – a lunar eclipse. The event lasts a couple of hours and can been seen from most of the Eastern Hemisphere; unfortunately not visible in the Western Hemisphere.
Fourteen days later, a solar eclipse occurs during new moon, only visible from the extreme South Pacific and Antarctica. In the meantime, we have some planetary and stellar close calls to observe. Sept. 8, Saturn and Neptune are within four and three degrees of the moon, respectively. The Pleiades are one degree away Sept. 12. By Sept. 16, Jupiter is five degrees south of the waning crescent moon, and the following day it’s two degrees north of the Beehive Cluster (M44). The morning of Sept. 19 sees a trio of the moon, Regulus, and Venus. Sept. 23 sees Spica in Virgo only 1.1 degrees from a barely visible thin crescent moon. Mars is four degrees north Sept. 24 and Antares (the opposite of Mars/Ares) is 0.6 degrees north Sept. 27.
Mercury is behind the sun, or too close to observe, all month.
Venus remains a Morning Star in the eastern dawn. Watch for a trio of Venus, Regulus, and the crescent moon Sept. 19.
Mars is tiny but visible in the western evening twilight. It passes 2 degrees north of Spica Sept. 12th.
Jupiter is prominent in the evening sky and through the night. The waning crescent moon passes five degrees to the north Sept. 16. Toward the end of the month, a series of double shadow transits of two Galilean moons occur at 3.5-day intervals.
Saturn is at opposition in Pisces Sept. 21, so the closest to us and furthest from the sun, making for prime observing and astrophotography. The Ringed Planet will be in retrograde motion for most of the month. Watch for the moon nearby Sept. 8.
Uranus begins retrograde motion Sept. 6 among the stars of Taurus, just to the south of the Pleiades. Its apparent westward motion continues for nearly six months.
Neptune is in southern Pisces all month, along with Saturn, and reaches opposition Sept. 23. At its extreme distance from the sun, the reflected light takes four hours to reach us.
The zodiacal light is visible before eastern morning twilight for the last two weeks of the month.
The autumnal equinox occurs in the afternoon of Sept. 22.
James Edgar has had an interest in the night sky all his life. He joined the Royal Astronomical Society of Canada in 2000, was national president for two terms, is now the editor of the Observer’s Handbook, and production manager of the bi-monthly RASC Journal. The IAU named asteroid 1995 XC5 “(22421) Jamesedgar” in his honour and he is a Fellow of the RASC.
