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By David Huestis, Historian, Skyscrapers, Inc.

Astronomical Events Determine Easter Observance

In simpler times our forefathers paid close attention to the clockwork motion of the heavens. One didn’t have to observe the sky for too long a period of time to notice the cyclic phases of the Moon, or the changing position of the Sun relative to the horizon over the course of a year. Nature provided a precise clock and calendar that could be used to determine when to celebrate special events.

It should therefore not be surprising that many religions observances would likewise be established in accordance with those same astronomical circumstances. Christians, for instance, observe Easter every year, but the date for the celebration changes. Since we can barely even remember birthdays and anniversaries that always occur on the same date, it’s time for me to enlighten you with the facts of how the date for Easter is determined.

Easter can occur as early as March 22 or as late as April 25. Why this range? The story began many moons ago when the Christian Church first developed. Since this holy day was determined in conjunction with Passover, Easter often fell on a weekday. However, in 352 CE the Council of Nicaea declared that it should always fall on a Sunday. They determined that Easter would fall on the first Sunday after the Full Moon on or next after the vernal equinox (spring—March 19, 20 or 21). However, if the Full Moon occurred on a Sunday, Easter is celebrated on the following Sunday. This scenario happened in 2001.

When I looked up the date for Easter 2019 (April 21) I immediately realized something was not right. When one has followed the motion of the heavens for as long as I have you can anticipate when and where events will happen. Being well aware of the “formula” for determining the date for Easter, I initially expected it would fall on Sunday, March 24.

Why? This year the vernal equinox was on Wednesday, March 20, at 5:58 p.m. EDT (Eastern Daylight Time). The Full Moon on or after that date occurred on the same day at 9:43pm EDT. Therefore, I calculated that Easter would be observed on the following Sunday, March 24, almost as early as it can be celebrated.

So why was my reasoning incorrect? Because of the fact that the vernal equinox date does vary, the Easter date depends on the “ecclesiastical approximation of March 21 for the vernal equinox” according to This stipulation holds true even if the vernal equinox falls on the 19th or 20th of March.

Considering this additional qualification using March 21 as the date for the vernal equinox, the next Full Moon after March 21 will be on April 19 this year. Therefore, Easter will be celebrated on Sunday, April 21. It is always a great day when you learn something new!

April Observing Opportunities

April is a fairly quiet month for most casual stargazers. Jupiter and Saturn are still early morning objects in a pre-dawn sky. Venus is still prominent but very low above the eastern horizon as the month begins. On the 11th you may spot Mercury about five degrees to the lower left of Venus. Mercury will only be about seven degrees above the horizon at 6:00 a.m. You’ll need an unobstructed view to the east to observe these two planets to best advantage. Venus’ brilliance will guide you to this sky location.

Just after sunset on April 13 you’ll find a waxing gibbous Moon within two degrees of M44, the Beehive Cluster of stars, in the constellation of Cancer. This conjunction of celestial bodies will look great with binoculars.

In addition, on the night of April 22-23, you should scan the skies for members of the April Lyrids meteor shower. The Lyrids are the oldest known shooting star display, having been observed by Chinese astronomers on March 16, 687 BCE. Being an old display, the number of meteors populating the stream of particles has greatly diminished. While some astronomers predict a rate of 15 meteors per hour under dark sky conditions, ten per hour is more likely.

However, a bright waning gibbous moon (full on the 19th) will reduce the peak number down to ten or less shooting stars per hour. The Lyrids are swift and bright meteors which disintegrate after hitting our atmosphere at a moderate speed of 29.8 miles per second. They often produce luminous trains of dust that can be observed for several seconds.

The Lyrids appear to radiate outward from an area of sky on the Lyra-Hercules border near the bright star Vega, which will be about 45 degrees (halfway between the horizon and zenith) above the eastern horizon at midnight and well placed for observing. I let my eyes roam the heavens while facing this general direction. Remember, even though you can trace back the dust train left by a Lyrid meteor back to its radiant point, members of this shower can appear anywhere in the sky.

And finally, on that same morning a beautiful sight will greet your eyes. Two and a half degrees to the lower left of the Moon will be bright Jupiter. Try using a camera with a telephoto lens, a pair of binoculars, or even a small telescope using low power to enhance your view of this beautiful sky scene.

Keep your eyes to the skies!