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: XXIX "I have loved the stars too fondly to ever be fearful of the night." -Sarah Williams THE DAILY ASTRONOMER Thursday, October 14, 2021 The Cassiopeia Clock Aliens, black holes, galaxy clusters, eclipses, and parallel Universes are all very well and intensely exciting. However, at times, one feels in the mood for more homespun astronomy, you know, the kitchen made Boysenberry jam astronomy stored in a mason jar and wrapped in cellophane with a frayed bow and quaint card bordered by hydrangeas and featuring a rabbit in a gingham pinafore standing by an oven in the corner.* In other words, simple night sky astronomy. So, today, we turn to the Cassiopeia Clock, a celestial device that will enable observers to keep track of the time. Yes, we know you don't need anything else to tell you the time as you already have smart watches, smarter phones, impatient relatives, and google speakers that will tell you the time, date, weather forecast, the first derivative of the hyperbolic secant and the thread count of Charlemagne's bedding. However, we're reverting back to the pre-digital age of turf fires, forest sorcery and skies unobscured by light pollution. One can see that the w-shaped Cassiopeia and the Big Dipper are diametrically opposed relative to Polaris, the north star. At our latitude, these are all circumpolar, meaning that they'll never set, at least not in our lifetime. Consequently, we can always find them in a clear sky anytime of night and anytime of year. [image: constsp.gif] As Earth rotates, the stars appear to revolve around Polaris, or, more correctly, the North Celestial Pole which is less than a degree away from it. Throughout a 23 hours, 56 minute period**, Cassiopeia and the other circumpolar constellations complete a circuit around the NCP. As this revolutionary period is slightly less than the day length, the position of circumpolar constellations shifts gradually over many weeks. The above image shows the positions of Cassiopeia and Ursa Major in the early evening spring sky. Notice that Cassiopeia is descending toward the horizon while Ursa Major is ascending toward its apex. However, after midnight, Cassiopeia begins its ascent in the northeastern sky and Ursa Major begins to move toward the horizon. In the summer early evening sky, Cassiopeia begins the night low in the northeast and ascends throughout the night. Cassiopeia is at its highest position by the pre-dawn. Cassiopeia begins the night high in the northeastern sky in early autumn and begins a descent toward the horizon after midnight One will see Cassiopeia in the northwestern sky in the early winter evening sky. The ancient queen descends toward the horizon throughout most of the night and by early morning appears along the horizon. Ursa Major will always appear opposite Cassiopeia. At times, Ursa Major will be easier to see than Cassiopeia because the latter will be low along the horizon. At other times, the situation will be reversed. We can watch these constellations quite easily in our lovely little stardome because the northern sky is toward the back of the theatre, the same location as the console. The true north, the north of the real world, is actually to the left of the dome's center and, of course, is duly marked.*** Even if you don't have a quaint star dome at your disposal, you can always find Cassiopeia in the northern star and, if you can dazzle your loved ones by using the celestial queen to tell the time. And, yes, being in a house littered with phone-worshipping teenagers, I am well aware that if it doesn't beep, flash or explode, it can't possibly dazzle. Give it a go, anyway. *Yes, that is what is known as the tidal spaghettification of a metaphor. **If Earth would only stay still and not revolve around the Sun, life would be so much simpler. However, the stars rise four minutes earlier each day as a consequence of Earth's revolutionary motion. For this reason, the circumpolar stars complete an orbit around the NCP every 23 hours and 56 minutes instead of 24 hours. ***This directional marking was necessitated by recently implemented University of Maine system consolidation protocol that requires us to genuflect three times a day in the direction of Orono. To subscribe or unsubscribe from the Daily Astronomer: https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A= <https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=1>