The heat of summer will come to an end in September, and the days and nights will reach equal length. Try to get out under the night sky a little more often and really begin to experience the beauty of our natural inheritance, the celestial events, always happening, through which the Earth and solar system move effortlessly, embedded in our vast Milky Way galaxy, deep within the universe that we are all connected to in subtle ways.

The autumnal equinox arrives at 5:05 a.m. Sept. 23 this year. The word equinox means “equal night.” There are only two days each year, the autumnal and vernal equinoxes, when everyone on Earth, except at the poles, will experience the sun rising due east and setting due west and equal days and nights. Due to our elliptical orbit around the sun, the days and nights are exactly equal a couple days after fall starts.

Additional Photos

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. Jupiter 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

Saturn is getting very low in the western sky now and will sink below the horizon by the middle of September. Fortunately, Jupiter will take its place soon after Saturn sets. The King of the Planets will rise around 10 p.m. at the beginning of the month, and it will rise two hours earlier by the end of the month. It is getting a little brighter and closer each night, approaching its opposition on Oct. 29. Try to see how many of its four Galilean moons you can see with just a pair of binoculars.

Mars now rises around 2 a.m. in Gemini. The red planet forms a straight line with the Twins brightest stars, Pollux and Castor, on the 15th. Its brightness is directly between that of the twin stars, at 1.4 magnitude. Its orange color is also very similar to that of Pollux, the immortal twin in Gemini. By the end of the month, Mars, which moves quite rapidly eastward against the fixed background of stars, will be entering the Beehive Cluster in Cancer. Mars moves one degree per day, which is 12 times slower than the moon, which always moves eastward one degree every two hours, or its own width, half a degree, every hour. Watch the waning crescent moon pass just below Mars about 90 minutes before sunrise on the morning of the 23rd, exactly when autumn begins. The next morning the moon will be 12 degrees farther below Mars.

Venus has been missing from our morning sky for a month now, and it will not return again until early next month in our evening sky. Mercury makes a brief appearance into our dawn sky during the first 10 days of September. Look for our first planet less than one degree to the left of Regulus in Leo half an hour before sunrise in the eastern sky on the morning of Oct. 9.

The planet Uranus will be at opposition on the evening of the 25th, just after fall starts. At magnitude 5.7, you could actually see it without binoculars from a perfectly dark sky. It can be found just below the circlet in Pisces. With binoculars, try to also find Neptune, which is just one more constellation to the west of Pisces, in Aquarius, both just below Pegasus the Flying Horse. Remember that Neptune has completed only one orbit around the sun since it was discovered in 1846, which is 165 years ago, nearly in the same place it is now. In a telescope, Uranus is a pale greenish disc, and Neptune is a wonderful shade of light blue.

These ice giants are each about four times the diameter of earth. This is a common size for planets in other solar systems — the Kepler mission has already discovered hundreds of new planets this size just in the last year. Uranus and Neptune are mostly made of water, ammonia and methane. By contrast, Jupiter and Saturn are mostly hydrogen and helium by mass.

As an additional challenge, you can also try to find the two brightest asteroids in September. They are in the same area of the sky just below Pegasus. The brighter one, Vesta, about the size of Arizona at 330 miles in diameter, will be about 6.5 magnitude in Capricorn. The other one, Ceres, is the largest of all asteroids, at 600 miles in diameter, or about the size of Texas, and will be in the eastern part of Aquarius at 7.6 magnitude. You will need binoculars to see them. Remember that the Dawn spacecraft, launched four years ago, just settled into a survey orbit around Vesta, 1,700 miles above its alien surface. It will continue to study Vesta for a year until it heads off for Ceres, which it will reach in 2015. The evolution of these two large asteroids is very different. They could both have become full-sized planets if the influence of Jupiter had not stunted their growth. We will learn many new amazing things about the formation of our solar system by studying these two asteroids in detail.

Sept. 1: On this day in 1979, Pioneer 11 became the first spacecraft to ever fly by Saturn.

Sept. 3: On this day in 1976, Viking 2 landed on Mars. The waxing crescent moon passes very close to Delta Scorpii, the middle bright star in the head of Scorpius.

Sept. 4: First quarter moon is at 1:39 p.m.

Sept. 5: On this day in 1977, Voyager 1 was launched to a highly successful and enlightening tour of our solar system. Only a very rare and fortuitous arrangement of the planets in our solar system made it possible for the two Voyager missions to visit the superior planets the way they did, using a gravity assist from one planet to slingshot it on its way to the next planet, all the way out to Neptune, our last planet.

Sept. 9: Mercury is less than one degree below and to the left of Regulus, the brightest star in Leo, half an hour before sunrise this morning low in the eastern sky.

Sept. 12: Full moon is at 5:27 a.m. Harvest moon, closest to equinox.

Sept. 16: Jupiter is to the right of the moon this evening. Ceres, the largest asteroid and the first one to be discovered, on Jan. 1, 1801, is at opposition tonight. That means it will rise at sunset and stay in our sky all night long.

Sept. 20: Last quarter moon is at 9:39 a.m.

Sept. 22: On this day in 1990, Pioneer 10 left our solar system.

Sept. 23: The autumnal equinox is at 5:05 a.m. Mars is to the upper left of the waning crescent moon this morning at the same time. The German astronomer, Johann Galle, discovered Neptune on this day in 1846. He found it within just one hour of searching for it and only one degree away from where the French astronomer, Urbain Le Verrier predicted mathematically that it had to be after wrestling with very difficult calculations for a full year. Some British astronomers were also involved in this fascinating story of discovery based on theory and math. John Adams essentially made the same calculations as Le Verrier but was not as sure of himself and never published his results to get the credit. It turned out that several people, including Galileo, had actually seen Neptune much earlier, but it doesn’t count if they didn’t know what they were looking at. They thought it was just another star.

Sept. 25: The planet Uranus is at opposition tonight. It can be seen in the constellation of Pisces below and to the left of the circlet with binoculars.

Sept. 26: Look for an extremely thin waning crescent moon a few degrees above the eastern horizon half an hour before sunrise this morning.

Sept. 27: New moon is at 7:09 a.m.

Sept. 30: On this day in 1995, daily communication with Pioneer 11 ended, after 16 years.

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

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