The Spring Equinox & zero right ascension hour

[Scooot]

I used to find it quite difficult to understand or picture exactly what these mean. I had read the equinox is when day hours equal night hours. I'd also read its when the sun meets the point where the ecliptic and the celestial equator cross. I also understood the concept of a sidereel clock but found it difficult to understand or picture where zero right ascenion hour was and why. That is until I could see it on a sky map.

So with the spring equinox approaching I thought I'd share my enlightenment for anyone else in a similar position.

The yellow line is the ecliptic. The white line is the celestial equator. The green shaded area is below the horixon. At 6am on 20th march they cross and the sun is positioned on them. It is the spring equinox. It is also zero right ascenion hour on the sidereel clock, illustrated by the curved white line going from bottom right to top left.

Move forward a month, and the sun is still more or less on the horizon at the same time but zero hour (the point where the ecliptic crosses the celestial equator) has moved forward, hence the moving ecliptic, and why the sidereel clock doesn't keep time with GMT.

[faulksy]

very good thanks for that