Talk:March equinox

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First Point of Aries vs. March equinox

The article says "In astronomy, the March equinox is the zero point of sidereal time and, consequently, right ascension." Shouldn't this be the First Point of Aries (sometimes called the vernal equinox)? The (J200) RA of the Sun is 0 at 23:58:8 GMT on 20/3/2022 according to Stellarium, not 15:33 UT. The First Point of Aries is the historical position of the March equinox.Yodo9000 (talk) 09:35, 27 May 2022 (UTC)

I don't accept your calculation. According to the United States Naval Observatory's computer program Multi-Year Computer Interactive Almanac (MICA) the parameter that defines the moment of the equinox, the apparent ecliptic longitude of the Sun, passed through 0 on March 20, 2022 between 15:34 and 15:35 Terrestrial Time. (UT1 and UTC would be about 15:33.) For conceptual purposes, the March equinox is when the Sun passes through the plane of the orbit from south to north, and the ecliptic longitude, ecliptic latitude, right ascension, and declination of the Sun are all 0. But due to the details of the modern definition these zeroes occur a few seconds apart. The MICA calculations reflect this.

"First Point of Aries" is a synonym for March equinox. "Vernal equinox" means spring equinox, but at the time the terminology was developing, most of the astronomers lived in the northern hemisphere, so to them, the spring equinox was the March equinox. In astronomy, "vernal equinox" usually means March equinox.

The First Point of Aries used to be in the constellation Aries a few thousand years ago when astronomers such as Ptolemy developed astronomical which were used for millennia in Europe, northern Africa, and western Asia. The point, and the event, is still the March equinox, but now the point is in the constellation Pisces. Jc3s5h (talk) 13:48, 27 May 2022 (UTC)

@Jc3s5h in that case, the dubious tag can likely be removed? MrAureliusR_Talk! 01:45, 21 June 2022 (UTC)

Looking more at this article and "First Point of Aries" they seem to them as two different things, but really the phrases are used almost interchangeably. Perhaps the articles should be merged. If not, there should be better cross-referencing.

Another problem with both articles is the articles treat a mental shortcut as a fact, which will be confusing for those not already familiar with the topic. When not thought of as a time, it is treated as a point, or location. An example is "it is one of the two points on the celestial sphere at which the celestial equator crosses the ecliptic." But in reality there is no celestial sphere, that is an imaginary sphere astronomers use to make speech and writing less awkward. (Perhaps astronomers actually believed in it before Newton.) In reality, when the March equinox is not being thought of as a time, it is being thought of as a direction. The article(s) should be revised to emphasize this. Jc3s5h (talk) 12:37, 9 July 2022 (UTC)

Please discuss here, but glance at the question about a merger at Talk:First Point of Aries#possible merger?. Also, I have notified WikiProject Astronomy. Jc3s5h (talk) 12:54, 9 July 2022 (UTC)