SKY GUIDE: This map represents the night sky as it appears over Maine during October. The stars are shown as they appear at 9:30 p.m. early in the month and at midmonth, and at 8:30 p.m. at month’s end. Jupiter and Saturn are shown at their midmonth positions. 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 Seth Lockman

The leaves have started to turn and soon much of New England will be ablaze with its famous flaming fall foliage. October always marks the first full month of autumn for us in the northern hemisphere. Just as our terrestrial landscape is transforming itself, now so our celestial landscape above us is also undergoing its gradual annual change from our familiar summer constellations like the summer triangle and Sagittarius and Scorpius to the more brilliant stars of Orion and the winter hexagon.

Since any given star will rise 4 minutes earlier each night, this is a gradual transformation, but it is quite noticeable over a week or two. The sky will look the same at 10 p.m. tonight as it will look at 8 p.m. next month on the same date. It changes by 120 minutes each month and completes its cycle of 24 hours each year.

The nights have already been cooler and crisper, and fall is usually the best time of year to get some consistently good skies for viewing before it gets too cold to stay out for long periods of time. It is always well worth going outside and looking up to enjoy and learn more about the many wonders that the cosmos is always offering us, but this is a particularly good month for that with each night getting a few minutes longer.

The highlights this month include Mars getting a little closer and brighter each night as we are catching up with it in our respective orbits, Venus getting higher and brighter in our evening sky as it catches up with Earth in its faster orbit around the sun, Saturn still close to its best as an evening planet, some nice conjunctions of the moon and planets, the annual Orionid meteor shower which peaks on Oct. 21, and a potentially brilliant comet that could light up our evening skies early this month if it survives its always perilous journey around the sun. Along with all of that we are still waiting for the Blaze Star, T Corona Borealis, to erupt as a recurrent nova and suddenly become about 1,000 times brighter in our evening sky.

Mars now rises around midnight to begin this month and it will rise by 11 p.m. by the end of October. It is moving in its normal eastward, or prograde, motion through Gemini now and it will enter the constellation of Cancer the Crab on Oct. 29. The red planet will start its retrograde, or westward motion, on Dec. 6 and it will reach opposition on Jan. 16 and then it will end its retrograde about a month after that, on Feb. 23.

Mars only reaches opposition every 26 months, so we only have about four months in every 26 months when Mars is close enough to Earth to spot some of its very interesting features in average amateur telescopes. That time will start near the end of September. We have sent 39 missions to Mars, and only 15 of them have been successful. Mars and even the moon still present some serious challenges to land on, even without any humans on board.

Venus is finally getting higher and brighter in our evening sky. It now sets fully 80 minutes after the sun in the western sky in the constellation of Libra the scales. Through a telescope you will see that Venus is 84 percent lit by the sun but even as that wanes it is getting brighter since it is getting closer to us and larger in our sky as our sister planet is catching up with us. Notice that a slender waxing crescent moon will pass very close to Venus on the evening of Oct. 5 and Mercury will join Venus by Oct. 24, but it will remain very low in the sky and you may need binoculars to spot our first planet.

Since Saturn is just past opposition now, it will already be up in our eastern sky as soon as it gets dark enough to spot it. It is still in Aquarius. Since it takes nearly 30 years to orbit the sun, the ringed planet will spend over two years in each of our 12 zodiac constellations. I saw a great view of Saturn through one of the telescopes at our club’s observatory in Kennebunk the other night with the shadow of the planet clearly visible on its rings along with three of its 146 moons. Its famous rings are now very thin, tilted open at only 5 degrees instead of its maximum of 27 degrees. The tilt will increase a little more and then it will decrease to zero in March of next year before it opens up again. This whole cycle happens twice every 29 years. Saturn is slowly getting smaller and dimmer again as it gets farther away from Earth. It is currently almost 100 times fainter than Venus, which now shines at minus 3.9 magnitude while Saturn is 0.7 magnitude.

Jupiter continues to get higher and brighter and rises a little earlier each night as it is getting closer to Earth approaching its opposition on Dec. 7. It now rises at 10 p.m. in Taurus and it will rise at 8 p.m. by the end of October. It will reach minus 2.7 magnitude, or only three times fainter than Venus. The Orionid meteor shower peaks on the night of Oct. 21. Unfortunately, the moon will be just four days past full, so it will interfere with the meteors when it rises around 9 p.m. and it will still be about 80 percent full in its waning gibbous phase. This shower will be active from Oct. 2 through Nov. 7. That is how long it takes the Earth to pass through all of the debris from Halley’s comet.

The last major highlight this month is a good possibility of seeing a very bright comet in our evening sky passing through Virgo into Serpens and Ophiuchus shortly after sunset from Oct. 13-21. This is Comet C/2023 A3 (Tsuchinshan-ATLAS). Tsuchinshan means Purple Mountain in Chinese after the observatory that first discovered it in 2023.

Many comets do not survive their journey around the sun if they pass too close to its powerful gravitational field and huge mass in relation to the tiny mass of the comet whose nucleus is usually only about 5 miles across. Many comets actually hit the sun on their perilous perihelion passes and others get torn up or greatly diminished which just happened recently to a comet that we had great hopes for but did not make it around. I call all comets the great imposters of the solar system since they look so impressive with their tails spanning up to 100 million miles and their comas, caused by the sublimation of their material due to their heating up and their proximity to the sun, reaching about the diameter of the earth while their nucleuses are only a few miles across.

This comet could become the brightest since one since NEOWISE which became very bright and easily visible below the Big Dipper a few years ago during the peak of the pandemic.

OCTOBER HIGHLIGHTS

Oct. 1: The Yerkes 40-inch refracting telescope was dedicated  in 1897. It was the largest telescope in the world at the time and it is still the largest refractor in the world now. It was designed by George Ellery Hale, who also designed and built the next three consecutive largest telescopes in the world culminating with the 200-inch Mt. Palomar reflector dedicated in 1948.

Oct. 2: New moon is at 2:49 p.m.

Oct. 4: The first satellite, Sputnik, was launched in 1957, beginning the Space Age.

Oct. 5: Neil deGrasse Tyson was born in 1958. … The moon passes 3 degrees south of Venus this evening.

Oct. 7: Niels Bohr was born in 1885. He was one of the pioneers of the quantum mechanics revolution that gave us the knowledge to make most of our modern technology possible.

Oct. 10: First quarter moon is at 2:55 p.m.

Oct. 14: The moon passes less than a degree north of Saturn this evening.

Oct. 15: Asaph Hall was born in 1829. He was an American astronomer who discovered Phobos and Deimos, the two tiny moons of Mars  in 1877.

Oct. 17: Full moon is at 7:26 a.m. This is also known as the Hunter’s Moon.

Oct. 19: The Indian-American astronomer, Subrahmanyan Chandrasekhar, was born in 1910. He discovered the Chandrasekhar limit of 1.44 solar masses that a red giant-white dwarf system will explode causing a Type 1A supernova which can used to determine distances to near the edge of the observable universe.

Oct. 21: The Orionid Meteor shower peaks tonight.

Oct. 22: Karl Jansky was born in 1905. He invented the radio telescope and discovered radio waves from the center of our galaxy in August of 1931.

Oct. 23: The moon passes 3 degrees north of Mars this morning.

Oct. 24: Last quarter moon is at 4:03 p.m.

Oct. 25: Henry Norris Russell was born in 1877. He created the Hertzsprung-Russell diagram to classify all stars in 1910.

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