September was the seventh month of the year when March was the first month. Fall always begins for us in the northern hemisphere this month and this will happen on Wednesday the 23rd at 4:21 a.m. The autumnal equinox is further defined by the sun on the ecliptic crossing over the celestial equator on a downward path, meaning the days are getting shorter and shorter.

The weather is usually at its best at this time of year, and the nights will be getting longer and cooler, so this will be a great month to get out and enjoy some of the natural wonders of the sky above us and the Earth beneath us.

SKY GUIDE: This chart represents the sky as it appears over Maine during September. The stars are shown as they appear at 10:30 p.m. early in the month, at 9:30 p.m. at midmonth and at 8:30 p.m. at month’s end. Saturn is shown in its midmonth position. To use the map, hold it vertically and turn it so that the direction you are facing is at the bottom. Sky chart prepared by George Ayers

That is one of only two days each year that the sun rises due east and sets due west for everyone on Earth except at the poles. The other day is the beginning of spring. Within a few days of that date is also the only time that the days and nights are exactly 12 hours long for everyone on Earth except at the poles. They are always 12 hours long at the equator.

This month’s highlight is a total eclipse of the Harvest Moon. This lunar eclipse will be the last in the current tetrad, which are four total lunar eclipses in a row with no partial eclipses in between. It will start on Sunday evening the 27th at 9:07 and the total phase will start at 10:11. The moon will begin to re-emerge out of our shadow at 11:23 p.m. and the partial eclipse phase will end at 12:27 a.m. Monday the 28th. The entire total lunar eclipse will last about 3 1/2 hours.

Not only will this be the most famous of the moons being eclipsed, but it will also be the closest Harvest Moon in a lifetime, since the eclipse will occur when the moon is less than one hour from perigee, which is its closest point to Earth for the month. So you don’t need to stay up particularly late or get up really early to see this one from right here in the Northeast. The entire eclipse will not be visible for the western half of our country.

Every lunar eclipse is unique. Watch closely and also try to photograph it to capture its beauty and to get a better sense of what is really happening. The shadow cone of Earth, which always extends about 1 million miles into space, will be sweeping across the moon at this time, which is about four times smaller than our planet.

Our atmosphere bends or refracts the sunlight around Earth and back onto the moon, allowing us to see it in many subtle shades of red and orange during the total phase. What you are really seeing is the combined effect of all the sunrises and sunsets on Earth simultaneously reflected back at us from the stark lunar surface. The more dust in our atmosphere at the time, the darker the lunar eclipse would be.

I just returned from the Stellafane convention in Springfield, Vermont. This is an annual pilgrimage for many amateur astronomers and always an exciting time to learn more about many aspects of astronomy, make new friends, reconnect with old friends and, most importantly, really experience and soak in the beauty of a pristine night sky a quarter-mile above sea level while magnifying tiny parts of it with larger telescopes than you could have access to anywhere else.

The bonus this year was catching many remaining Perseid meteors, though it was a couple of nights after their peak. There is nothing like witnessing the pitch dark sky sprinkled with its random arrangement of softly glowing stars and other celestial objects suddenly being silently split apart by a brilliant streak of light that leaves a twisting trail of matter high in our atmosphere. You can get a better sense of the real nature of our life-sustaining atmosphere as you attentively watch exactly how our protective envelope of precious air absorbs and extinguishes these tiny sand-grain size objects safely as you see this silent streak.

I gained a much better appreciation for Pluto, and all the work and luck that went into making this a successful mission that will continue for many more years by listening to Alan Stern, the chief investigator for the New Horizons mission that just got to the dwaft planet on July 14 after 91/2 years of high-speed travel.

Pluto is turning out to be quite an active place with moving nitrogen and methane ice mountains, and an atmosphere that is four times thicker than we first thought. It looks more like Mars with its orange and reddish colors. There are many mysteries still to be uncovered here as we try to develop plausible mechanisms that could explain some of what these great high resolutions imply.

Saturn is now setting about three hours after sunset into the western sky even as it is drifting farther away from us as Earth leaves it behind in our faster orbit around the sun. The ringed planet is still an impressive sight in the constellation of Scorpius. Watch as the waxing crescent moon passes close to it on the evening of Friday the 18th.

Venus, Mars and Jupiter are all in the morning sky now. Look for them about evenly spaced one hour before sunrise in the eastern morning sky toward the end of the month. Before that you will only see Mars and Venus in the morning sky. Watch and try to photograph as a slender waning crescent moon passes right between Venus and Mars on the morning of Thursday the 10th.

Venus starts September as a large, slender crescent and finishes much smaller and one-third lit by the sun as our sister planet races ahead of us in our continual orbits around the sun.

SEPTEMBER HIGHLIGHTS

Sept. 3: In 1976, Viking 2 landed on Mars.

Sept. 4: The waning gibbous moon will occult Aldebaran in Taurus at midnight. The star will then re-emerge about an hour later from behind the dark limb of the moon. Watch with binoculars so that you will get a sense of the continual motion of the moon. Also try to photograph this event.

Sept. 5: Last-quarter moon is at 5:54 a.m.

Sept. 11: In 1985 the International Cometary Explorer made its first fly-by of a comet and it also flew by Halley’s Comet the next year. It was placed in a Lagrangian orbit where the gravitational forces of Earth, sun and moon are perfectly balanced so that gravity seems to be suspended in those areas. We lost communication with this satellite in February 2014.

Sept. 13: New moon is at 2:41 a.m. There will also be a partial solar eclipse today, visible only over Antarctica and part of South Africa.

Sept. 17: In 1789 William Herschel discovered Mimas, the smallest and innermost of Saturn’s seven largest moons. Mimas is 250 miles in diameter, has a giant crater that covers one- third of its surface and has a four-mile-high central peak.

Sept. 23: Autumn begins at 4:21 a.m. for us in the Northern Hemisphere. On this day in 1846 Johan Galle discovered Neptune very close to where Urbain LaVerrier predicted it would be. Neptune just completed its first orbit around the sun four years ago after its discovery. Its 165-year orbit has a perfect 2-to-3 resonance with Pluto’s 248-year orbit. There are about 12 other Kuiper Belt Objects with this resonance and they are all called Plutinos.

Sept. 27: A total lunar eclipse takes place starting at 9:07 this Sunday evening and ending at 12:27 the next morning.

Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.

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