[Remind-Fans] Beginning of spring

[Dianne Skoll]

On 3/21/19 6:33 AM, Matthias Teege wrote:

> On a give occasion I've tried to calculate the beginning of spring
> (day and night same lenght) in remind. I've played with
> [sunrise(trigdate()) - sunset(trigdate())] but is not exact enough. Is
> it possible at all, to calculate the beginn of spring in remind? Any
> hints?

In general, it's not possible.  The equinox is NOT defined as the
date when day and night are as close in length as possible.  Here in
Ottawa, that would have been March 17th this year:

https://www.timeanddate.com/sun/canada/ottawa?month=3&year=2019

There's an explanation here:

https://www.timeanddate.com/astronomy/equinox-not-equal.html

Here's a Remind script that prints "Equinox" on the day in March whose
day length is as close as possible to 12 hours.  It is *NOT* the same as
the first day of spring and is *NOT* the official Equinox.

Regards,

Dianne.

#==================================================================
# Length of the day
FSET daylen(x) sunset(x)-sunrise(x)

# Get the crossover date - only works in northern hemisphere!!!
# For southern hemisphere, change the >= and <= around.
REM March SATISFY [(daylen($t) >= 12*60 && daylen($t-1) <= 12*60)]

# Get the two day lengths
set d1 daylen($t)
set d2 daylen($t-1)
set d $t

# Pick the one closest to 12 hours (=720 minutes)
IF abs(d1-720) < abs(d2-720)
   REM [d] SCANFROM [today()-7] MSG Equinox
ELSE
   REM [d-1] SCANFROM [today()-7] MSG Equinox
ENDIF