What are the correct symbols for vernal and autumnal equinox?

Question

What are the correct symbols for vernal and autumnal equinox?

I have seen people use both ♈︎ (\Aries) and $\gamma$ (\gamma) to denote vernal equinox. However, I have never seen the symbol for autumnal equinox. Should it be either ♎︎ (\Libra) or $\Omega$ (\Omega)?

Are ♈︎ and ♎︎ the conventional symbols to use?

Are $\gamma$ and $\Omega$ sometimes used just because they resemble the above symbols?

An alternative name for vernal equinox is First Point of Aries. Is there a similar name (First Point of Libra) for autumnal equinox?

Answer 1

The Wikipedia article on astronomical symbols says:

The zodiac symbols are also sometimes used to represent points on the ecliptic, particularly the solstices and equinoxes. Each symbol is taken to represent the "first point" of each sign. Thus, ♈ the symbol for Aries, represents the March equinox; ♋, for Cancer, the June solstice; ♎, for Libra, the September equinox; and ♑, for Capricorn, the December solstice.

The article cites Roy and Clarke, Astronomy: Principles and Practice. This question copies an example usage of ♈ and ♎ from that book. Stellarium uses the same symbols if you set View: Markings to show the equinoxes and solstices.

$\gamma$ is a poor substitute but clear enough if ♈ is unavailable. Since $\Omega$ stands for an orbit's longitude of ascending node (angle ♈-☉-☊), it would be a confusing substitute for ♎.

"First point of Libra" is archaic but correct. These names and symbols represent tropical zodiac signs, not IAU constellations. ♎ is fixed at ecliptic longitude 180° regardless of constellation boundaries. Its location in Virgo this century doesn't change its name or symbol.