March 20
The Equinox
Sun Position
The Sun crosses the celestial equator northward today (vernal equinox, Northern Hemisphere; autumnal equinox, Southern Hemisphere), at 0° declination, every point on Earth receives approximately 12 hours of daylight and 12 hours of darkness, and the Sun rises and sets due east and west.
Sky Highlight
The vernal equinox (Northern Hemisphere) and autumnal equinox (Southern Hemisphere) occur on or very near March 20 each year. Day and night are nearly equal in length across the globe, the Sun rises due east and sets due west from every location on Earth, and the ecliptic crosses the celestial equator at the First Point of Aries, which due to axial precession now lies in Pisces.
Deep Sky Object
M104 (Sombrero Galaxy), a spiral galaxy in Virgo with a prominent dust lane, about 31 million light-years away; it sits on the border with Corvus and is best placed in spring evenings. Its distinctive shape is visible even in modest telescopes. Best seen from latitudes between +60° and -50°.
Featured Star
Naos (ζ Pup) is a blue supergiant 1,080 light-years away in Puppis, spectral class O4If(n)p, one of the hottest and most luminous stars observable with the naked eye, with a surface temperature near 42,000 K and a luminosity over 500,000 times the Sun. It is a runaway star, likely ejected from the system that produced the Vela supernova, traveling at high velocity through the galaxy.
Around This Date
- March 20, 1916Albert Einstein submitted his completed paper on the general theory of relativity to the Prussian Academy, providing the mathematical framework governing gravitation, spacetime curvature, and the large-scale structure of the universe.
- March 20, 1727Isaac Newton died in London; his Principia Mathematica had established the laws of motion and universal gravitation that described every known planetary orbit with unprecedented precision.
The equinox is the sky's one truly democratic moment: equal day and night for every latitude, the Sun rising due east for every person on Earth.