Equinox

===Names===
* Vernal equinox and autumnal equinox: these classical names are direct derivatives of Latin (''ver'' = spring, and ''autumnus'' = autumn). These are the historically universal and still most widely used terms for the equinoxes, but are potentially confusing because in the southern hemisphere the vernal equinox does not occur in spring and the autumnal equinox does not occur in autumn. The equivalent common language English terms ''spring equinox'' and ''autumn (or fall) equinox'' are even more ambiguous.<ref name="Skye2007">{{cite book |first=Michelle |last=Skye |title=Goddess Alive!: Inviting Celtic & Norse Goddesses Into Your Life |url=https://books.google.com/books?id=s1x2ATL66UcC&pg=PT69 |year=2007 |publisher=Llewellyn Worldwide |isbn=978-0-7387-1080-8 |pages=69ff}}</ref><ref name="Curtis2013">{{cite book |first=Howard D. |last=Curtis |title=Orbital Mechanics for Engineering Students |url=https://books.google.com/books?id=2U9Z8k0TlTYC&pg=PA188 |year=2013 |publisher=Butterworth-Heinemann |isbn=978-0-08-097748-5 |pages=188ff}}</ref><ref name="GrewalWeill2007">{{cite book |first1=Mohinder S. |last1=Grewal |first2=Lawrence R. |last2=Weill |first3=Angus P. |last3=Andrews |title=Global Positioning Systems, Inertial Navigation, and Integration |url=https://books.google.com/books?id=6P7UNphJ1z8C&pg=PA459 |year=2007 |publisher=John Wiley & Sons |isbn=978-0-470-09971-1 |pages=459ff}}</ref> It has become increasingly common for people to refer to the September equinox in the southern hemisphere as the Vernal equinox.<ref>{{cite book |last=Bowditch |first=Nathaniel |department=National Imagery and Mapping Agency |title=The American practical navigator: An epitome of navigation |url=https://books.google.com/books?id=pXjHDnIE_ygC&pg=PA229 |year=2002 |publisher=Paradise Cay Publications |isbn=978-0-939837-54-0 |pages=229ff}}</ref><ref>{{cite book |title=Exploring the Earth | year=2016 |url=https://books.google.com/books?id=hs-PBSZTCBMC&pg=PT31 |publisher=Allied Publishers |isbn=978-81-8424-408-3 |pages=31ff}}</ref>
* [[March equinox]] and [[September equinox]]: names referring to the months of the year in which they occur, with no ambiguity as to which hemisphere is the context. They are still not universal, however, as not all cultures use a solar-based calendar where the equinoxes occur every year in the same month (as they do not in the [[Islamic calendar]] and [[Hebrew calendar]], for example).<ref name="LaRocque2007">{{cite book |first=Paula |last=La&nbsp;Rocque |title=On Words: Insights into how our words work – and don't |url=https://books.google.com/books?id=7VPSb8py5jUC&pg=PA89 |year=2007 |publisher=Marion Street Press |isbn=978-1-933338-20-0 |pages=89ff}}</ref>  Although the terms have become very common in the 21st&nbsp;century, they were sometimes used at least as long ago as the mid-20th&nbsp;century.<ref>{{cite book |title=Popular Astronomy |url=https://books.google.com/books?id=CcEzAQAAIAAJ |year=1945}}</ref>
* [[Northward equinox]] and [[southward equinox]]: names referring to the apparent direction of motion of the Sun. The northward equinox occurs in March when the Sun crosses the equator from south to north, and the southward equinox occurs in September when the Sun crosses the equator from north to south. These terms can be used unambiguously for other planets. They are rarely seen, although were first proposed over 100&nbsp;years ago.<ref>{{cite book |title=Notes and Queries |url=https://archive.org/details/notesandqueries06whitgoog |year=1895 |publisher=Oxford University Press}}</ref>
* [[First point of Aries]] and first point of [[Libra (astrology)|Libra]]: names referring to the [[zodiac|astrological signs]] the Sun is entering. However, the [[precession of the equinoxes]] has shifted these points into the [[constellation]]s [[Pisces (constellation)|Pisces]] and [[Virgo (constellation)|Virgo]], respectively.<ref>{{cite book |title=Spherical Astronomy |url=https://books.google.com/books?id=9KFRhcsn8-UC&pg=PA233 |publisher=Krishna Prakashan Media |pages=233ff |id=GGKEY:RDRHQ35FBX7}}</ref>