Adirondack Sky Center
Tupper Lake, New York
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Astro Quiz 20: What's the Vernal Equinox?

Question #20 – On Wednesday, March 20th, the northern hemisphere will experience the vernal equinox. What does this mean?

Answer:

The simple answer is... it is the first day of spring! At least it is for the northern hemisphere.

Because the Earth travels around the Sun each year tilted at a 23½ degree angle, the celestial equator (the extension of the Earth's equator on to the sky) is not on the same plane as the ecliptic (the path that the Earth and the planets travel around the Sun).

There are two days each year when the plane of the ecliptic and the celestial equator intersect; both of these days are called the equinox. As we view the Sun on those days, it rises due east and sets due west. We also have equal amounts of daylight and darkness. When the sun crosses the celestial equator from south to north, people in the northern hemisphere experience the vernal (spring) equinox. The days start to become longer than the nights until the summer solstice, the longest day of the year.


The spring equinox occurs at 5:58 pm on March 20, 2019. At this time, the Sun
will be exactly at the intersection of the celestial equator (the red line) and the ecliptic (green line)
Image created with Starry Night Pro 8 Plus

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