THE SOUTHWORTH PLANETARIUM 70 Falmouth Street Portland, Maine 04103 (207) 780-4249 usm.maine.edu/planet 43.6667° N 70.2667° W Altitude: 10 feet below sea level Founded January 1970 2021-2022: II " 'Water? What do you mean by that? I don't understand it.' This is what a fish would say if it had a human mind." -Eckhart Tolle "The Power of Now" THE DAILY ASTRONOMER Thursday, September 2, 2021 September 2021 Night Sky Calendar Part I No, autumn has not yet started! The cult of preternaturally chipper meteorologists has designated September 1st as the first day of autumn. Well, the sect of even perkier astronomers insist that fall will not commence until the autumnal equinox which, this year, occurs on September 22nd. So, don't pack away the SPF 50 sunscreen, surf boards and the various other estival accoutrements -never seen in northern New England anyway- quite yet. Nearly three weeks of summer remain! And what occurs in late summer along the celestial plane? Orion returns to the pre-dawn eastern sky as Virgo dissolves into the dusk. The Summer Triangle reaches the apex at 9:00 p.m. while the Great Square of Pegasus -the largest of the autumn constellations- ascends in the east. The moon continues inexorably along its phase cycle while the planets weave their elegant loops among the stars. The same ceaseless activity the Stonehenge builders observed continues tonight. We select a few celestial events for inclusion in our monthly night sky calendars. These events are either the easiest to observe or are important enough to be mentioned. Granted, this judgement is quite subjective. To ardent skywatchers, no event is unimportant. True enough. And, we would love to include events such as: "Look for asteroid 532 Herculina tonight. This magnitude 10.9 object, 91 times fainter than the dimmest naked eye star, is careening through deep interplanetary space within the region of Cetus. See the fine star chart below." [image: skychart.png] However, our space, unlike that of the cosmos, isn't infinite. We must be discriminatory. Yet, we acknowledge that for every event we post, thousands are occurring in our sky; trillions throughout the galaxy; an incalculable myriad in the Universe. As we do try to incorporate a great deal of information and images into this calendar, we separate it into parts. *Wednesday, September 1: Finding the North Star in our sky* A perfect way to begin the new school year is by finding the north star Polaris. Consider Polaris to be our cynosure: the one steady point in our dynamic whirlwind of a Universe. No matter how far afield we travel in space-time, Polaris will remain the one constant.* By locating this star, one can also determine the cardinal directions in the night sky. To find Polaris, one should first find the Big Dipper, an asterism within the constellation Ursa Major: [image: Ursa_Major_-_Ursa_Minor_-_Polaris.jpg] Image courtesy of heavensabove.com The Big Dipper is *circumpolar*, meaning that it will not set at all during the year. (At least not in our lifetimes.) The outer bowl stars, Dubhe (alpha) and Merak (beta) point directly to the north star Polaris. If one could press a tack into Dubhe so as to allow the Dipper to rotate around that star, the Dipper's end handle star Alkaid could reach almos to Polaris. *Thursday, September 2, 2021: Finding Polaris in the Northern Hemisphere* [image: slide_9.jpg] Polaris has been useful to navigators for centuries because of its close alignment with the north celestial pole. A northern hemisphere observer could determine his/her latitude simply by measuring the angle separating Polaris from the northern horizon. For instance, in Portland (ME), Polaris is about 43.5 degrees above the northern horizon because Portland is 43.5 north of the equator. An observer along the Tropic of Cancer would see Polaris 23.5 degrees above the northern horizon. A skywatcher at the north pole would see it directly overhead. *Friday, September 3, 2021: Moon near Pollux* Castor and Pollux are the two brightest stars in Gemini the Twins, one of the thirteen *zodiac constellations*, defined as those constellations through which the Sun appears to move during the year. The Sun's actual path, called the *ecliptic, *is represented by the purple arc in the image below. [image: skychart (2).png] Image courtesy of heavensabove.com The moon and planets also travel along a band centered on the ecliptic. Consequently, the moon and planets will often, but not always, move through the same constellations as the Sun. These night sky calendars will often include close passages of the moon with bright stars and planets. Tonight, one will see the waning crescent moon (13% illuminated) close to Pollux. The moon and Pollux will rise by 2:00 a.m. They are best seen after 3 a.m. when they will both be more than 15 degrees above the eastern horizon. *Monday, September 6, 2021: New Moon* There is nothing to see here. When the moon is new, or in *conjunction*, it is located between the Sun and Earth and is not visible. Of course, when the moon moves directly in front of the Sun, the new moon is visible as a dark disk against the Sun. We refer to such events as solar eclipses. Oh, and... [image: 4th-of-July-Fireworks-4.jpg] *Only 949 days until the April 8, 2024 total solar eclipse! Throughout the DA school year, we'll be discussing this spectacle in far greater detail.* *Wednesday, September 8: Moon near Mercury* An observer will see Mercury and the waxing crescent moon (6% illuminated) in the western evening sky tonight. Both Mercury and the moon will set by 8:15 p.m. [image: skychart (4).png] Image courtesy of heavensabove.com *Friday, September 10, 2021: Moon near Venus (Silver event!!)* For those who've just joined us, we assign ratings to the top three -sometimes top four- events. The moon-Venus appulse is often one such event. Look for the waxing crescent moon (14% illuminated) and brilliant planet Venus in the western evening sky. Both the moon and Venus vanish by 9 p.m. *So, here we allowed ourselves a great deal of licence. First, Polaris is not precisely aligned with the North Celestial Pole. Secondly, the north star changes over time due to Earth's precessional wobbling. For instance, travel back to watch the construction of Egypt's Step Pyramid (circa 2630 BCE) and one would have noticed that Draco's Star Thuban served as the North Star. Conversely, jump ahead in time to around 15,000 AD and one would see that the new North Star would be Vega, the brightest star in the Summer Triangle. 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