Snow here. But the Sun is on its way to thaw us, coming up like a seal through a breathing-hole in a sheet of ice, the plane that is the celestial equator.
The spring equinox (spring for our northern hemisphere) is at March 20, Tuesday, 16:15 Universal Time. That is, for the Central time zone of North America, 10:15 AM. It will be daytime, so our picture is drawn for night-time a few hours earlier, near the middle of the night between Monday and Tuesday.
It shows the state of the night sky, its arch from east to west, with the arches of the equator and ecliptic, at the time when the Sun is at the crossroads of those two arches. (I hope that isn’t a mixed metaphor; two arches could have a crossroads, couldn’t they?)
To cram these great arches into a picture, the scale is twice smaller than for my usual horizon scenes. Ecliptic, equator, and horizon are all “great circles” on the celestial sphere, not really either convex or concave; for this picture it seemed better to make the horizon concave (the focus is 10 degrees above the south point).
A picture like this seems to be all curves, because it is projected on the inside of a celestial sphere. But it’s full of right angles (spans of 90 degrees) along great circles. A right angle from the horizon to the zenith; a right angle along the ecliptic from the Sun to the “antapex of Earth’s way”; another from there to the “anti-Sun” point; two right angles (180°) from the west point on the horizon to the east point; and two right angles from where the Sun is on the ascending node of ecliptic over equator, to the opposite or descending node.
In the west, Venus and Mercury went down shortly after the Sun. The Moon, nearly three days old, will have been slender but easy at sunset; at this clock time two days hence it will be still just above the horizon, nearly at midnight.
Higher in the west, in Taurus, is the “antapex of Earth’s way,” the direction from which we are hurtling in our orbit. Nearing the middle, because the time is nearly midnight, is the “anti-Sun” point, or shadow of Earth. It is bout to reach the opposite crossroads of ecliptic and equator.
Over in the east, Jupiter has just risen. As it and the anti-Sun move toward each other, they will meet – that is, Jupiter will be at opposition – on May 9.
Saturn, about 3 hours of right ascension (of the sky’s turning) behind Jupiter, will follow it to an opposition on June 27.
I’m not sure how to connect “equinox” and “font” – perhaps by swapping metaphors, a fons or spring in the icy surface of the celestial equator, instead of a blowhole for the Sun Seal – but I do want to say that I am very glad I thought of asking your advice on the font I should use in a book. There have been 21 comments, all thoughtful and useful, and when I am sure they are complete I will make a joint report.
As too often, when you think you’ve coined a word, the internet disabuses you. Equifonts exist, but unlike the aequinoctium or “equal night” they have nothing to do with equality; they’re systems for watering equi, horses.
Does an equifont ensure equality or equity? Do all horses get the same amount of water, or does each horse get enough water for its needs? (Tee, hee.)
I’ve been reading a bit about spherical trigonometry and non-Euclidian geometry (which I prefer to think of as post-Euclidian). Dana Mackenzie’s book _The Universe in Zero Words: The Story of Mathematics as Told through Equations_ has an interesting chapter, “The Geometry of Whales and Ants”. On the surface of a sphere (whether the outer surface, as the surface of the Earth, or the inner surface, as the celestial sphere), the sum of the inner angles of a triangle will always be more than 180 degrees. You can draw a circle with three right angles, adding up to 270 degrees, e.g. from the north pole to the equator at zero degrees longitude (or zero hours of right ascension), along the equator to 90 degrees longitude (or six hours right ascension), and then back to the north pole. At each vertex of the triangle you’re making a 90 degree turn. I can feel the inside of my head stretching a bit!
And I’ve been enjoying watching the Sun rising a bit farther north each day on the ridge of Potrero Hill, and the gradually lengthening days. But I found the abrupt switch to Daylight “Saving” Time last week quite stressful. Starting DST at the end of Winter is cruel, especially for those of us who work 8 to 5 jobs. What would otherwise be a sweet time of gradually lengthening days becomes a sudden shock of sleep deprivation and fatigue.
There is at present a large online petition for abolition of “Daylight Saving Time” – I forget whether it’s Chhange Org, Credo, or what. I left a comment that I hoped they’re appealing for return to standard time, not the crazy idea of going to the shifted time for the whole year. My argument against “Clock-changing” is in a block on page 31 of Astronomical Calendar 2016, but I have a more extended piece on it that I don’t think I’ve printed or uploaded anywhere yet.
The spherical triangles Anthony mentions are something I had to tackle at a certain stage of programming; I see that it took eight “subroutines” to deal with them. That is, finding sides from angles or vice versa, in spherical triangles with or without a right-angled corner.
There was a bill in the California state legislature to allow the voters to decide whether or not to continue observing daylight saving time. I was mildly optimistic that we might join Arizona in ignoring this idiocy. But the bill was not passed by the legislature, so for the time being California will continue observing daylight saving time.
There was a story on National Public Radio recently that Florida wants to go to permanent daylight saving time. There is no way to do this under current federal law, so Florida is trying to get moved to the Atlantic time zone, despite the fact that Florida is farther west than all the Atlantic seaboard states north of South Carolina.
Spherical trigonometry is challenging but intelligible. Human folly truly boggles the mind.
Well said. I’ve heard it put another way – the trouble with common sense is that it isn’t.