#SOLSTICE AND EQUINOX 2021 HOW TO#
#SOLSTICE AND EQUINOX 2021 CODE#

'Map times into linear functions crossing zero at each syzygy' Note that for angles near 90 or 270, increasing angles yield decreasing results Into smooth functions crossing zero, for root-finding algorithms. '''Map angle values in degrees near the quadrants of the circle # TODO: Are these the right functions to call for the definition of syzygy? Geocentric? True? 'Return ecliptic longitude of the sun in degrees at given time (MJD)' Return Time(mjd, format='mjd', scale='utc') 'Return a Time object corresponding to the given Modified Julian Date.' # But going over 50,000 years back, season lengths can vary from 85 to 98 days! # given time, except when it is is within a few days of a cross-quarter day. # We'll usually find a zero crossing if we look this many days before and after # TODO: need to ensure we're using the right sun position functions for the syzygy definition.

#SOLSTICE AND EQUINOX 2021 CODE#

The code is also in a gist, which might get refined: see find syzygy / equinox / solstice with astropy # Find the nearest syzygy (solstice or equinox) to a given date. I employed sin(angle*2) in the (poorly named) linearize(angle) code below to convert ecliptic longitudes to a function which crosses zero at each quadrant. Since Earth doesn't have seasons shorter than 88 days within plus-or-minus 50,000 years, that's hopefully a pretty safe bet, and the astropy ephemerides aren't accurate for that long anyway. But rather than looking for the next syzygy, it looks for the nearest one, by picking points 44 days before and after the given date and expecting that there will be one syzygy in between those dates.

#SOLSTICE AND EQUINOX 2021 HOW TO#

How to handle that?Īs you expected, the syzygys can be located using scipy.optimize, via a root-finding function, as in the code snippet below. ) How do I find the next time (from a particular origin, for example now) when the Sun's longitude is zero? How do I find the previous time when it was zero? Also, the vernal equinox seems to be a particularly nasty case for solving, since the function has a discontinuity at that point – it jumps from 360 to 0. The Sun's longitude is an angle, so there are obviously many solutions for lon=0 (this year's equinox, next year's equinox.

My first thought was to use something from scipy.optimize to solve this function for time, but at this point, I got stuck. SunEcliptic = sun.transform_to(eclipticOfDate) Sun = _body('sun', t)ĮclipticOfDate = (equinox=t) So it seems that getting the ecliptic longitude of the Sun would be the essential step, and then I could somehow solve that function for time: def sunEclipticLongitude(t): However, there are no such functions in astropy, so I thought I might try to compute the times by the definition: the vernal equinox is the moment when the ecliptic longitude of the Sun is zero the summer solstice is the moment when the ecliptic longitude of the Sun is 90° etc. I have worked before with the pyephem package, and it provides easy functions exactly for this: one can, for example, say > print(ephem.next_equinox(ephem.now()))Īnd get the time of the next equinox. PT.I would like to use the astropy package to compute the time of equinoxes and solstices. In fact, Earth is closer to the sun during winter than it is in the summer months.įor those who don't like jack frost nipping at their noses, mark your calendars: The first day of spring, also called the vernal equinox, happens on Sunday, March 20, at 11:33 a.m. The tilt of the Earth - not our distance from the sun - is what causes winter and summer. During the winter solstice, the Northern Hemisphere is tilted at its farthest distance from the sun, bringing less light and colder temperatures. The 23.5-degree tilt in Earth's axis of rotation creates a rise and fall appearance of the sun over the course of a year. In the Southern Hemisphere, it's the summer solstice and the longest day of the year. 21, marking the official start of the astronomical winter and the shortest day of the year for the Northern Hemisphere. The 2021 winter solstice occurred at 10:59 a.m. The winter solstice marks the shortest day of the year in terms of hours of daylight.

Solstice and equinox 2021