Autumn always begins for us in the northern hemisphere in September.

This year that will happen at 9:54 p.m. on Saturday the 22nd. This will mark the end of a long, hot summer as the nights will cool off and get more transparent even as they are getting shorter, already heading toward winter again.

The autumnal and the vernal equinoxes are both interesting days on Earth because they mark the only two days each year when the sun rises due east and sets due west for everyone on Earth except for the poles. Within a few days of the equinoxes are also the only two days each year that are exactly 12 hours long for everyone on Earth except for the poles. The reason for that is our slightly elliptical orbit around the sun and our 23.5-degree tilt on our axis.

The days are always 12 hours long at the equator and they don’t experience any seasons, but the rest of the world does. The seasonal changes are especially enjoyable in New England because there is a slow and continual transformation going on both in our view of the sky above us and on the Earth below as we are always orbiting the sun and just tilting one hemisphere or the other a little more toward this life-giving natural force that affects everything.

The highlights this month include all four of the brightest planets still being visible in our evening sky at the same time. There will also be some nice conjunctions of the moon with all of those planets, but no good meteor showers until next month.

Venus is the brightest of the four and the first one to set in the west, about one hour after sunset. Notice that it will be just one degree to the lower left of Spica in Virgo early this month. Our sister planet is still getting brighter in our sky as it continues to catch up with us in its orbit. We have already passed our other neighbor, Mars, but both are still much closer to Earth than usual. Venus continues to get brighter even as it gets less illuminated by the sun. It will be only 18 percent illuminated, similar to a waning crescent moon, by the end of the month.

Then continue east along the ecliptic and you will encounter Jupiter in Libra, just one constellation to the east of Venus. Notice that Venus will be catching up with Jupiter during the month, closing that gap to just 14 degrees by the end of it. Jupiter has been back to its direct, eastward motion in the sky since the middle of July. So the king of the planets continues to fade a little more as we are pulling farther ahead of it. It starts the month setting around 10 p.m. and ends the month setting 2 hours earlier.

Jupiter is still very close to a double star in Libra with the long Arabic name of Zubenelgenubi, but it is slowly drifting farther away from this star whose name means “the southern claw.” Libra used to be part of Scorpius, the next constellation to the east.

Then continue eastward along the ecliptic about 30 degrees, the biggest gap between any of the four planets now visible, and you will encounter Saturn in Sagittarius. Its rings are still tilted open near their maximum of 27 degrees, even though it is slowly dimming since it is a few months past its opposition now. You will easily see its largest moon, Titan, through a telescope and you could even see four or five more moons on a good night.

The last one in this great planetary lineup that has been with us all summer now is Mars. The red planet was at its best in 15 years just last month, but it will still be much brighter and larger than usual for another few months. It even got brighter than Jupiter last month, but Mars will fade a little more this month and become less bright than Jupiter again on the 7th as the Earth is now pulling farther ahead of the red planet in our faster orbit around the sun.

I was able to see some detail on the Martian surface through several telescopes last month. I could see some dark markings and a hint of both the north and south polar ice caps. I didn’t see any of the Martian atmosphere this time because of some planet-wide dust storms that are covering much of its surface.

There will be four close lunar conjunctions with the planets this month as the moon will nicely highlight each of those planets as they move on their appointed paths along the ecliptic. We start with the slender crescent moon pointing out Venus on the 12th, then it will be just 4 degrees north of Jupiter on the 13th, then only 2 degrees north of Saturn on the 17th, and finally it will end this cycle 5 degrees north of Mars on the 20th. The moon moves about 12 degrees eastward along the ecliptic each day.

I attended the annual Stellafane convention last month. This is the oldest and one of the largest star parties in the world. Nearly 1,000 avid amateur astronomers attended this summer. It was held during the peak of the Perseid meteor shower and near new moon. This is an annual pilgrimage for a diverse group of people that share a common interest. Everyone learns new things there and shares new experiences as they peer through hundreds of great telescopes at the heavens above, always obtaining new views of our familiar sky and its myriad contents as we expand our cosmic perspective of where we really are all the time.

There are hands-on workshops as well as many great presentations for everyone. I attended some on astrophotography, light pollution, variable stars, and binoculars. The main speaker was Samuel Hale, the grandson of George Ellery Hale, the most famous telescope maker in the world, who designed and built the four largest telescopes in the world from 1898 through 1938.

Todd Mason also gave a great presentation. He made the documentary “Journey to Palomar” and now creates computer graphics of the largest new telescopes in the world to show people what they look like and how they will really work when completed. These include the Large Synoptic Survey Telescope that will find thousands of potentially hazardous asteroids, the Giant Magellan Telescope with its seven-mirror segments equal to 25 meters, and the Extremely Large Telescope with a 39-meter mirror, nearly 4 times larger than the largest telescope in the world today. They should see first light within seven years or so and they will likely completely revolutionize our current limited understanding of our universe.

Sept. 3: On this day in 1976, Viking 2 landed on Mars, just weeks after Viking 1.

Sept. 9: New moon is at 2:03 p.m.

Sept. 12: The moon will be near Venus tonight.

Sept. 13: The moon will be near Jupiter tonight.

Sept. 16: First quarter moon is at 7:16 p.m.

Sept. 17: The moon is near Saturn tonight.

Sept. 20: The waxing gibbous moon will be near Mars tonight.

Sept. 22: Fall begins today at 9:54 p.m. as the sun crosses downward over the celestial equator.

Sept. 23: J. Galle discovered Neptune on this day in 1846. Two other astronomers calculated exactly where this planet should be based on its influences on other planets. Neptune is at its best in Aquarius now, but you will need a telescope to see it. It had only made one orbit by 2011, 165 years after it was discovered.

Sept. 24: Full moon is at 10:54 p.m. This is the famous Harvest Moon since it is closest to the equinox.

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

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