The days of solstices and equinoxes


Introduction

"E pur, si muove !" - literally "And yet, it rotates !" -, claimed Galileo Galilei after he was sentenced for heresy in 1633. Yes, our Earth does rotate. It rotates around its own axis, on the one hand, revolves around the Sun, on the other hand. Viewed from earth, it is however the Sun which seems to make this daily rotation and this yearly revolution as well. Doesn't it effectively rise at the north-eastern corner of the local horizon and set at its north-western corner on summer solstice ? Doesn't it appear at the south-eastern corner of the sky and disappear at its south-western corner six months later, on winter solstice ? Aren't the length of its diurnal trajectory and the height of its upper transit in the southern meridian responsible for the duration of the day ? A duration which equals 12 hours on spring and autumn equinoxes.


Trajectory of the Sun above the terrestrial horizon on summer solstice (left),
on spring and autumn equinoxes (center) and on winter solstice (right),
viewed from the northern hemisphere.


The use of this software will lead you to easily and accurately determine the days on which the summer and winter solstices as well as the spring and autumn equinoxes fall on any year between 4712 BC and 2017 AD. Simply enter the year considered and the longitude of the site chosen for observation, then the software, which was conceived on the basis of algorithms developed by the Astronomers of the Bureau des Longitudes, Paris, will automatically generate the days and hours (Universal Time and Local Solar Time) at which these remarkable events occur.


About this software : This software leads to determine the days of solstices and equinoxes any year between -4712 and 2017. Dates of first publication and successive updates of this software : october 2003 / july 2010
Author of this software : Karine Gadré, Doctor in Astronomy of the University of Toulouse, France, Founder and Header of the Culture Diff' company, Associate Researcher at the Research Institute in Astrophysics and Planetology (IRAP), joint reseach unit of the University of Toulouse and the CNRS (UMR 5277).

Exclusively at Culture Diff' : Make a free test of this sofware. Use it to determine the days of solstices and equinoxes in 2012 AD, next discover its functionalities and possible use.
Software + : This software was conceived within the context of the doctoral dissertation I prepared at the Laboratoire d'Astrophysique de Toulouse-Tarbes, Toulouse, France, on the basis of the most recent developments into Astrometry and Photometry. It led to identify every one of the old Egyptian decans to stars visible with the naked eye of the Hipparcos catalog.

Access to the user interface

The price of this original astronomy software is 5 euros. This amount includes an unlimited access to the user interface and a free access to any future updates. To purchase this software by credit card or PayPal balance on the PayPal secure payment server, add it to your PayPal Cart. To do so, please click on the following logo :

Secured electronic paiement


Further Culture Diff' resources

Dossiers > AstroEgypto : The Egyptian decans : mythical stars
Dossiers > HistoSciences : Astronomie antique et moderne : d'observations en modélisations toujours plus poussées
Publications > Wiki AstroEgypto : Introduction aux méthodes de l'archéoastronomie. Première Partie : Application à l'identification des décans égyptiens



Bibliography

Borkowski, K.M., "ELP 2000-85 and the Dynamical Time - Universal Time Relation", Astronomy and Astrophysics, 205 (1988), L8-L10.
Bureau des Longitudes, "Introduction aux Ephémérides Astronomiques", EDP Sciences 1998.
Centre de Données Astronomiques de Strasbourg : http://cdsweb.u-strasbg.fr .
Chapront-Touzé, Michelle et Chapront, Jean, "Lunar Tables and Programs from 4000 BC to AD 8000", Willmann-Bell, Richmond, 1991, pp 6-7.
JPL Horizons : http://ssd.jpl.nasa.gov/horizons.html.
Simon, J.L., Bretagnon, P., Chapront, J., Chapront-Touzé, M., Francou, G., Laskar, J., "Numerical expressions for precession formulae and mean elements for the Moon and the planets", Astronomy Astrophysics 282, 663-683 (1994).
Stephenson, F.R., "Historical Eclipses and Earth Rotation", Cambridge University Press, Cambridge, 1997.
Stephenson, F.R. et Morrison, L.V., "Long-Term Fluctuations in the Earth's Rotation : 700 BC to AD 1990", Philosophical Transactions of the Royal Society of London, Ser. A, 351 (1995), 165-202.
Stephenson, F.R. et Morrison, L.V., "Long-Term Changes in the Rotation of the Earth : 700 BC to AD 1980", Philosophical Transactions of the Royal Society of London, Ser. A, 313 (1984), 47-70.