When was the last time there was a full or new moon on the spring equinox?

Answer 1

That depends on how picky you want to get about definitions.

The full moon and new moon occur at precise instants of time -- when the longitude of the Moon is equal to the Sun, the Moon is new *at that instant*, and when the longitude of the Moon is 180° from the Sun, the Moon is full *at that instant*.

Meanwhile, the spring equinox occurs when the longitude of the Sun is zero, which is also an instantaneous event. So if you want to wait until these two events occur at the exact same instant, you'd have to wait centuries or millenia.

But most people consider the Moon to be full or new for oh, about a day or so -- even though the Moon moves 13° per day through the sky. So let's allow for that kind of slackness and say that the Moon only has to be within 6.5° of new or full to meet these conditions.

In that case, there were full moons on the spring equinox in 1905, 1924, 1943, 1962, 1981, and 2000. The next such occurrence will be in 2019.

There were new moons on the spring equinox in 1920 and 1939. The next such occurrence will be in 2034.

Answer 2

How close do you want it?

The Spring Equinox is a mathematical moment in time (duration = 0); it is the moment that the centre of the Sun (on its apparent path around the ecliptic) crosses the celestial equator. One second before, it is still to the south of it, one second later it is to the north of it.

The Full Moon (or New Moon) are also mathematical moments of duration 0; the moment that the angle Sun-Earth-Moon reaches its maximum (or minimum) monthly value. One second before the Full Moon, the angle is still increasing; one second after, the angle is already getting smaller.

If we take that the "day of the equinox" lasts a total of 24 hours (12 hours on either side of its moment) and that the day of Full Moon also lasts 24 hours (12 hours on either side of its moment), then the full Moon could occur during the interval of 24 hours before to 24 hours after (a period of 48 hours).

In terms of the Moon orbit, the time of Spring equinox is an independant variable (there is no link between the two events). So it can occur at any point during the Moon's cycle.

The Moon's cycle (Full Moon to Full Moon) lasts an average of 29.530589 days = 708.73414 hours.

What is the probability that Spring Equinox, which can occur anytime during this 708.7 hour cycle, occurs during a particular 48-hour period?

48/708 = 0.067726... = 6.77% = 1 / 14.76

If you accept any of Full Moon or New Moon: since the probability for each is equal (in other words, two 48-hour periods during the same 708 hour cycle), then the probability is double: 13.54% or 1 / 7.382647...

It should occur (on average) every 7.38 years.

In 2007, New Moon occured 45h24m before Equinox (more than the 24 hours we seek), so 2007 was not such a year.

2004: New Moon was 15h52m after Equinox.
2000: Full Moon was 2h51m before Equinox. Still, in New York (or anywhere in the Eastern Standard Time zone), Full Moon occured on Sunday evening, March 19, local time, and Spring Equinox was on Monday morning, March 20, local time: not on the "same day"

Answer 3

I'd say 2004 (new) or 2000 (full). 2000 definately. Possibly somewhere in the world you could barely seen the moon on the equinox of 2004? Then it wouldn't be new for them