On Apr 20, 7:32*am, Difei wrote:
Greetings all,

In Chapter.26 of Jean Meeus's Astronomical Algorithms, he introduced a
way to calculate the JDE of the equinoxes and solstices of a given
year. And we all know the apparent longitude of the Sun corresponding
to these calculated JDEs would be 0, 90, 180 and 270 degrees,
respectively.
My question is how can I calculate the JDEs corresponding to other
apparent longitudes, say, 15, 30, 45, 60 degrees, etc. Any idea would
be helpful, thanks in advance.

Cheers,
Difei

The title of the thread should be 'how to use the calendar based Ra/
Dec system' which predicts rather than calculates different celestial
events from solstices to solar eclipses ect.

Solstices and equinoxes are orbital events and although it is fine for
the man on the street to talk in terms of Spring equinox,summer
solstice and things like that,in astronomical terms these things
disappear and the events are demarcated as the December solstice or
the September equinox as these relate to specific orbital
characteristics as the planet turns through 360 degrees to the central
Sun in generating a single orbital daylight/darkness cycle.

You want to be a mechanical monkey then good for you,the system you
are using is based on a proportion of 1461 rotations for 4 orbital
circuits but more importantly,it is grouped in batches of 365 and 366
rotations rather than the raw rotational orbital proportion of 365 1/4
rotations to 1 orbital cycle.

In case you are wondering,what you are asking is a step below
geocentricity which is homocentricity,you will know this as the axis
of a telescope tracking a circumpolar star,which unfortunate people
imagine substitutes for constant and steady rotation,creates its own
individual axis of rotation and far removed from the North/South Polar
coordinates which reader here believe they are witnessing.You need to
be an astronomer to know the differences,some of these things are
intricate and empiricists often exploit these intricacies for
obfuscation purposes and therein is the tragedy,the timekeeping system
we inherited is incredible,even the convenience of the Ra/Dec system
has its purposes but there are limits to what that system represents.