November is regarded as a bleak month–
No sun–no moon!
No morn–no noon–
No dawn–no dusk–no proper time of day.
No warmth, no cheerfulness, no healthful ease,
No comfortable feel in any member–
No shade, no shine, no butterflies, no bees,
No fruits, no flowers, no leaves, no birds!–
–to quote, yet again, the most quotable put-down of this hapless month (Thomas Hood’s “No!”).
But what is revealed when darkness falls and our dank atmosphere is peeled away is such an evening sky as might make us want to promote November to first month of the year, over March or January (the historic rivals for that title). What is revealed is the first sidereal hour, otherwise known as the Andromeda Hour. At least, that’s the name I’ve suggested for it.
Around 9 or 10 p.m. on a November evening, it’s sidereal time One. What is Sidereal Time? It isn’t a head shop where you can buy sandals or beads or incense or thyme or dashikis or lava lamps or pot, though it almost became that: when I was living among the flower people of California, one of them heard me mention it and exclaimed: “Sidereal Time! Cool! Spacey! Far out! That’s the name I’ll use!”
Later, I learned that the Albuquerque Astronomical Society called its newsletter The Sidereal Times. Why didn’t I think of that?
We divide the starry (sidereal) sky around us into 24 hours. That’s the celestial mapping system, corresponding to longitude for mapping the Earth. The mighty star Betelgeuse is at right ascension 6 hours, meaning it is 90 degrees of the way around the map. When Betelgeuse is passing over for you, the sidereal time for where you are is hour 6.
The sidereal time neatly describes the state of the sky as you see it. If Betelgeuse is up there in the middle, then Orion (of which Betelgeuse is part) stands upright, Leo is rising in the east, the Great Square of Pegasus is sinking in the west, and so on. We could call this whole picture the Orion Hour.
Well, sidereal time 1 occurs when Andromeda passes over. Instead of Betelgeuse, the “star” object that crosses overhead at this time – almost exactly overhead, if you are at about latitude 40 degrees north – is the Great Andromeda Galaxy. That is the lamp, faint but famous, that hangs on the meridian.
At the Andromeda Hour, Pegasus is also close to the meridian, since the constellations of Andromeda and Pegasus are almost joined (they share a star). Perseus is a little to the east, climbing toward the meridian. Orion has only just risen and is still lying on his back. Aquila the Eagle is going down tail-first in the west. The Milky Way arches close to overhead, from east to west. Of the two bright skymarks that perpetually whirl around the Pole Star, Cassiopeia is high and the Big Dipper is low to the northern horizon. That is the state of things at the Andromeda Hour.
The point about a sidereal time is that it can occur at any time by our earthly clocks. The Andromeda Hour is the state of the sky around 9 or 10 on a November evening, but each evening it arrives gradually earlier, so that in December it is the state of the sky around 7 or 8. If you are camping out in September and wake at midnight, you are looking up at the sky of the Andromeda Hour. At midday in March you can’t see any stars at all, but if you suddenly could, you’d see the Andromeda Galaxy at the zenith and the rest arrayed around it as the Andromeda Hour.
Each other of the twenty-four Hours has its turn to fill the evening sky, and each has its character, so they are a great way to describe the annual round of the sky and to become familiar with its features.
The special thing about the Andromeda Hour, or sidereal time 1, is that at this time a certain vast and related set of constellations is entirely in view.
I won’t regurgitate my whole piece about the Andromeda Hour from my cover picture story for Astronomical Calendar 1976. Let’s see how compressedly the story of the Royal Family of the Sky can be told (reluctantly omitting dozens of side-plots).
An oracle warned king Acrisius of Argos that his daughter Danae’s baby Perseus would grow up to kill him, so he had them both thrown into the sea inside a chest. It grounded on an island and was pulled out by a fisherman. Polydectes, king of the island, wanted Danae, Perseus (now grown) protected her, Polydectes tricked him into promising to go and slay Medusa. She was one of the three Gorgon sisters, had snakes for hair and was so ugly that beings turned to stone at sight of her. By looking at her reflection in his shield, Perseus cut off her head, and from her blood sprang the winged horse Pegasus. Flying on Pegasus over the coast of Palestine, or of Ethiopia, Perseus saw Andromeda chained to a rock. Her mother Cassiopeia had boasted of being more beautiful than the Nereid sea-nymphs, so a sea monster, Cetus, was sent to ravage the land, and could only be sated by the sacrifice of Andromeda. Perseus slew Cetus, married Andromeda, flew back with her to the island, rescued his mother from Polydectes, flew back to Argos, accidentally killed his grandfather with a quoit. Not wanting to take the kingdom of Argos in this way, he instead founded Mycenae nearby. About the only Greek hero with more stories to his name was his great-grandson Hercules.
And in the sky at the Andromeda Hour you can see Perseus; Pegasus; Andromeda; Cetus the monster or whale; Cassiopeia; her husband Cepheus; and, in Perseus’s hand, the sinister “winking” star Algol which is the petrifying eye in the head of poor Medusa.
But not Hercules. Oh, yes, you just can, he has set up to his waist in the northwest. He is overhead about sidereal hour 17. And not Odysseus, who, come to think of it, has more stories still, but he is more like a character in a novel than in a myth and no one thought of making him into a constellation.
This is part of my large sky-dome picture for Astronomical Calendar 2012 showing the sky at the Andromeda Hour, with the Great Galaxy in the middle and the hours of right ascension shown as stripes, like the gores from which a skirt or a balloon is made.