Stars over Sisters 9/28/2021


Last updated 9/28/2021 at Noon

With autumn’s arrival, temperatures have begun to cool as the sun sinks ever lower in the sky as the season progresses. We’ve even had a touch of much-needed rain. The shortening days and lengthening nights will also lead to more opportunities for stargazing.

While it is true that the evening constellations are dimmest during this time of year, most of them can still be identified under a clear, moonless sky. One of these is our featured constellation for this month, namely Triangulum, the celestial triangle. Though small, this stellar grouping isn’t quite so hard to spot because of its distinctive shape and slightly brighter stars. Look for it in the eastern sky around 7 p.m. between the constellations of Andromeda and Aries.

The constellation’s brightest star, Beta Trianguli, is a giant white star that shines at third magnitude. Though it has yet to be confirmed, astronomers suspect that this star may be a binary, separated by less than five a.u. from its stellar companion (one a.u. is the average distance between the sun and the earth). The pair has an orbital period of about 31 days. Beta Trianguli is estimated to be approximately three-quarters of a billion years old (much younger that our sun’s age of 5 billion years) and lies at a distance of about 127 light-years.

For a relatively small constellation, Triangulum contains many deep sky objects, almost all of them dim, distant galaxies. The lone exception is Messier 33, otherwise known as The Triangulum Galaxy. What makes this object noteworthy is its proximity to our Milky Way Galaxy. Only the Andromeda Galaxy is thought to be nearer. M33 is estimated to be populated with 40 billion stars and measure about 60,000 light-years in diameter.

Little if any mythology stems from Triangulum, but its shape inspired several different interpretations. Probably the best known of these came from the Greek and Egyptian cultures who knew the constellation as Deltoton, because of its resemblance to the capital Greek letter delta. The Romans said it represented the island of Sicily. In Babylonian star catalogues, the star Gamma Andromedae was included with Triangulum, forming a constellation known as “The Plough.”

Beginning on October 16, a 21-day window of opportunity opens in which NASA plans to launch a first-ever space probe designed to fly by eight asteroids over a 12-year period. Known as the Lucy Mission, its goal is to gather data that researchers hope will provide clues about the ancient material from which the outer planets of our solar system formed. Seven of the targeted bodies are Trojan asteroids that are clustered near the orbit of Jupiter. The eighth is a main belt object situated between the orbits of Mars and Jupiter. The mission’s name comes from the 3.2-million-year-old hominin skeleton dubbed “Lucy” by its discoverers.

Saturn and Jupiter still reside in the constellation of Capricornus the Sea Goat this month. Both are visible in the south-southeastern sky at nightfall. Saturn sets at 12:24 a.m., Jupiter follows at 1:47 a.m. Even though brilliant Venus will stand a full 47degrees from the sun on October 29, it will continue to hang low in the sky because of the shallow angle of the ecliptic to the southwestern horizon.

Mercury pops up in the morning sky during the last two weeks of the month. Mars is still in conjunction with the sun and won’t become visible again until December.

Early in the month will be an ideal time to get a good look at the beautiful night sky as there will be no evening moon visible in the sky. By October 9 a waxing moon will become evident, that will culminate in the Full Hunter’s Moon on October 20.

This month’s dark-sky awareness tip to help fight light pollution here in Sisters is this: as it gets darker earlier switch out your light bulbs to warmer colored lights to preserve our dark skies and, if possible, add a motion sensor so that your lights are only being lit when needed!


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