#astronomy
How to find the vernal point in the sky?
The vernal point (aka 'Aries') is the intersection of 2 lines in the sky: the celestial equator and the ecliptic.
On its way along the ecliptic, the Sun reaches the vernal point at the... vernal equinox (March 20 or 21, 5 days ago).
The vernal point is used as an origin to define 3 angles: right ascension, ecliptic longitude and sidereal time (yes this one is an angle too).
The vernal point sweeps across the sky in a day. This simple instrument helps you find its position.. with the help of the Sun.
Tilt the disc according to your latitude (side scale).
Align it along your local N-S direction.
Turn the wheel so the stick's shadow hits the current date : the arrow points to the vernal point.
The outer digits give you the sidereal time. If you try 24h later the vernal point will have changed position, bc its period is 23h56min. Hence the calendar scale.
To make your own: just download & print the pdf from here (instructions in french). Made with #Python & #LaTeX
https://www.astrolabe-science.fr/horloge-siderale-solaire/