NavList:

Hello everyone,

My understanding is that the March equinox also determines the first point of Aries.

By looking a the nautical almanac, I see that on March 20 at 09 hs 00 min, both GHA of the Sun and Aries have the exact same value:

GHA Sun: 313° 09.0' (with South declnation 00° 00')

GHA Aries: 313° 09.0'

However, I see in the previous messages that the real time of the equinox was about 1 minute at 30 seconds later, which means at 09hs 01' 30"

By calculating the GHA of the Sun and Aries at that time, now we get different GHA's, which makes sense because the sky (aries) rotates at a faster speed than the sun:

GHA Sun 313° 31.5'

GHA Aires 313° 31.6'

In the case of the Sun, after 1' 30'  the GHA difference would be about 22.5 minutes, which will cause a significant position error when doing the sight reduction.

I am far from being an Astronomer, so I would appreciate if someone could explain the reason of these differences.

Thanks !!!

Martin Caminos