On Wednesday May 20 the Sun enters the sign Gemini. This gives us a rather good way of seeing the difference between “signs” and constellations.
See the end note about enlarging illustrations.
The “signs” of Aries, Taurus, etc., still used in astrology, are 30°-wided bands along the ecliptic, starting at longitude 0°, the “First Point of Aries.” The constellations are areas of the starry sky, defined since 1930 by lines. The two coincided, somewhat more than two thousand years ago, when the system of signs was defined. But precession – the wobbling of Earth’s spin axis over a cycle of 25,800 years – has made them increasingly divergent.
The chart shows the Sun’s travel from March 20 (the spring or vernal equinox) to May 20. You can see that the Sun does indeed reach longitude 60° on the ecliptic. But this brings it to the beginning (roughly) of constellation Taurus, not Gemini. It will have to travel another 30° – a month – to enter Gemini.
The stars and constellations stay fixed. What shifts over time is the celestial equator – the “belt,” you could say, of the spinning Earth – and the mapping system based on it.
Mentally move them. Imagine the Sun’s March-to-May track, and the celestial equator = the two features I’ve emphasized with red – slid 30° to the left (east), while everything else stays in place. The crossing-point of equator and ecliptic – which is the zero point for longitude – is 30° to the left: it is at what is now longitude 30°, the beginning of Aries. So it really is then the “First Point of Aries.” The Sun is at it in March, and arrives at the gates of Gemini at this time in May.
This was how things stood when the system of signs was agreed, around two thousand years ago.
You can, with some imagination, see it in your sky.
There is the Sun (below the horizon) at its May 20 position where it enters the “sign” Gemini. If this were 150 BC it would be 30° on, at what is now longitude 90° – the solstice point of our time, by the feet of Gemini.
With less need of imagination, and more of binocular aid, you can see Venus for one of the last times before it plunge into the glare of the Sun. The arrows through the moving bodies indicate their motion over five days, against the starry background. So you can see that as the Sun continues to advance in its usual way, Venus is falling back toward it.
And in the background Mercury is hurrying out toward its eastern elongation of June 4. So the two inner planets will have a conjunction on <ay 22, less than a degree apart. I hope I haven’t already made the joke about the planets failing to observe social distancing.
One of whose effects is to give us training in mental geometry.
Before social distancing, there were social media. Before social media, there was socialism. And before socialism, there were the Social Wars. Do you know what they were?
They were the wars, in 91, 90, and 89 BC in which the Romans subdued their related Italian tribes, whom they called socii or “partners” because they had been on the same side in earlier wars.
Another bit of linguistic shifting has to do with the well-bandied word “pandemic.” Epidemic is from Greek epi, “on,” and dêmos, the “people,” so its root meaning was something (not necessarily a disease) that was “prevalent among the people.” So the Greek word that has become our pandemic meant “of the whole people, popular, vulgar.”
__________
ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format. You may be able to enlarge them on your monitor. One way: right-click, and choose “View image”, then enlarge. Or choose “Copy image”, then put it on your desktop, then open it. On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers). Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.
Sometimes I make improvements or corrections to a post after positing it. If you click on the title, rather than on ‘Read more’, I think you are sure to see the latest version.
This weblog maintains its right to be about astronomy or anything under the sun.
Another good bunch of Pan’s are the theological positions; pantheism: God and the universe are one, panentheism: God and the universe are one but God is also outside of it, pandeism: God created the universe out of itself and withdrew into the fabric of the universe but has nothing to do with it’s day to day workings, panpsychicism: everything is conciousness and conciousness created the universe not the other way around.although many of these stances seem to overlap and confusion reigns for example I have read one claim that the ancient philosopher, Plotinus,was a dualistic pantheist (also claimed for Plato) and another that he was a panentheist.
And then there’s the god Pan, who has little patience for theological conundrums, preferring to entertain the nymphs with sweet tunes on his pipes.
I just noticed that you have m35 down as a globular cluster on your map but I believe that it’s an open cluster.i was lucky that I mixed up the night of the Venus and Mercury conjunction and saw them both last night the 20th as the 21st has been cloudy .
You’re right. M35 is a large open cluster, and globular cluster NGC 2158 can be seen through its southwestern edge, as I mention several times in the Astronomical Companion. I’m not going to correct my blog diagram now because life is short.
NGC 2158 is also classified as an open cluster. Wikipedia says it was previously thought to be a globular cluster, but is now considered, “an intermediate-age, metal-poor open cluster that is a member of the old thin disk population.” The age is listed as 2 billion years, which is a relatively long time for the stars of an open cluster to hang together, but only a fraction of the lifetime of even the youngest globular clusters.
Another one in dispute but generally now classified as a globular is m71 in Sagitta.
My favorite astronomical chameleon is Omega Centauri. Over the centuries this object has been considered a star, a nebula, a globular cluster, and most recently the remnant core of a dwarf galaxy that was absorbed by the Milky Way galaxy.
I live at 38 degrees north latitude, and Omega Centauri is at 47.5 degrees south declination, so theoretically this star / nebula / globular / galactic core culminates 3.5 degrees above my southern horizon, but in practical terms it’s always obscured by haze. Last night I was on a hill with a clear view to the south, and Theta Centauri, 11 degrees north of Omega, was culminating and caught my eye. When I was in Hawai’i to see the 2012 transit of Venus, clouds prevented me from also seeing Omega Centauri. If I ever get to the tropics again, or to the southern hemisphere, I hope to see this thing for myself.
Thanks for the etymology lesson.
I didn’t know that epidemic wasn’t necessarily related to disease but it makes sense after you pointed out the root words. I did know that “epi” meant above or on, like the epicenter being the point on the surface of the Earth directly above the fault that caused an earthquake. Likewise, epidermis is the layer of skin above the dermis.
“Pan” means all, thus pandemic means affecting the whole world. Pan is also used in Panama (connecting North, Central, and South America) and pander (where one uses their wit to sell something to the general population).
I also didn’t know that vulgar referred to the whole population. If elite members of society spoke in the vernacular of the masses they would be referred to as being vulgar.
The derivation of “Panama” is unknown (it may have been a word in an indigenous language); “pander” is from Pandarus, a character in the legends of Troy – he procured Cressida for Troilus. Your ideas of connecting the words with pan, “all”, are ingenious, but may be examples of folk etymology. The airline company Pan Am presumably does intend to convey the idea of “all” “America”.
My favorite example of folk etymology is something I heard in Arab Jerusalem from a scholar who claimed that many English words are derived from Arabic: “influenza” is from `anf al-anza, “nose of the goat”,
It was a stretch to connect Panama to Pan America. I was probably thinking about the airline that you mentioned. Pander was also a poor example considering Pandarus. Better examples are panacea or panorama.
I liked your example of folk etymology. Maybe a goat’s nose tends to be wet like the nose of someone with the flu. It actually makes more sense than my Random House dictionary that says influenza comes from the same root as influence. Influence comes from “flow in”, such as a tributary flowing into a bigger river. Not sure how influenza and influence would be connected; possibly from the virus flowing into the body or the virus influencing the onset of symptoms.
I did find an interesting connection between influence and astrology. Astrologers believe that stellar emanation of ethereal fluid “flows into” humans to affect their actions or destinies.
I opened the window and in flew Enza.
2 months to traverse 30 degrees of longitude. That is some wobble.
I don’t understand the bottom illustration with the arrows, long curve, and three indecipherable figures. What is it?
I’m bilingual in signs and constellations. Signs relate to the seasons and the wheel of the year. The Sun crosses the first point of Aries at the moment of the northern hemisphere Spring equinox. At Beltane the Sun is halfway through Taurus. At the Summer solstice the Sun enters Cancer. Etc.
We can’t see the stars when the Sun is up during the day, so we need to use the Moon and planets to correlate the tropical zodiac signs with the constellations. In addition to the feet of the Gemini constellation marking the Summer solstice point, other memorable landmarks (skymarks?) are Regulus precisely at the first point of the sign of Virgo, Beta Virginis at the Fall equinox point, the Winter solstice point in the cloud of steam above Sagittarius’ teapot, and the first point of the sign of Aquarius near Beta Capricorni.
My silly sketch was meant to show pedestrians walking in opposite directions and a cyclist trying to social-distance from both – a common sight on, for instance, the Thames bank path. Perhaps in California you aren’t seeing so much of the social-distancing culture.
I have to steer a course between those who say “Grr!” if I seem to give the slightest sympathy to astrology and those like you who understand the persistent value in the alternative system.
Aha. We’re looking from above the north pole of the bicyclist’s cranium. It makes sense now.
Social distancing is a fraught subject here in San Francisco. Most people are being careful and considerate. Too many people are obliviously absorbed in their smart phone, or walking and talking in groups across the entire sidewalk and not making way for others. Some runners and bicyclists, most not wearing masks, zip tightly by walkers. A few demented souls are either completely unaware of the situation or taking advantage of it to express their impotent rage by frightening passersby. Way too many people are wearing masks around their neck, pulling them up over their mouth and nose only when they think they need them. I don’t have a car, so I get around on foot and bicycle, and I go to work at my clinic on BART, our regional train system. With most people either out of work or working from home, BART ridership is down over 90%, and they’re still running full length trains, so there’s always plenty of space, especially on the first train car. Everybody is supposed to wear a mask on BART, but some don’t, or are using their mask as neckwear.
It tickles my mind to switch between a geocentric perspective, watching the planets move through the sky, and a heliocentric perspective, picturing the planets in their orbits around the Sun. As you say in the introduction to the Astronomical Companion, most people today are more familiar with abstract theories than with how things immediately appear in the sky.