January 17, 2018

Astro-Event:The Vernal Equinox.

Batten down the hatches; spring is here in a most astronomical way. The vernal equinox occurs this Saturday, March 20th at 17:32 Universal Time; expect uniform amounts of sunshine and darkness worldwide as well as a Sun rising directly due east and setting due west. The spring equinox is also used in the reckoning of Easter; this year’s Paschal or Easter Full Moon falls on March 29th and the proceeding Sunday and Easter falls on April 4th. This year, Eastern Orthodox Easter also falls on the same date; The Orthodox church uses the older Julian calendar and hence the two don’t always coincide. In fact, this year’s date is the earliest that an Eastern Orthodox Easter can fall.

Wake up a little late for work this Monday? That’s because we’re currently back on ye’ ole Daylight Savings Time… follow Astroguyz on Twitter, and never be caught unaware again!

Also, keep an eye out for a decent occultation of the Pleiades by the Moon on the evening of the 20th, the same date as the equinox… the waxing crescent Moon will either lie close to or occult several bright stars, depending on your location. This is the last in a series of lunar-Pleiades occultations until 2023.

This week’s Astro term is: Atmospheric Refraction. Does it seem as if the body of that equinox Sun didn’t rise precisely at the predicted time? Refraction induced by the atmosphere is the primary culprit. Not only does this deflection of visible light cause objects to shift position, but it also causes stars to shimmer, and gives the Sun and Moon a bloated, distended shape. Refraction is always greatest at the horizon, and can be most easily observed over the sea or at high altitude. For this reason, astronomers almost always try to observe objects in transit, when they’re highest overhead and thus present the least amount of distortion. Turbulence and humidity can also play a factor, and refraction also occurs across the electromagnetic spectrum.

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