July 31, 2015

If you look to the East this evening – just before sunset – you will see a Blue Moon rising.

From here in Nanaimo, the best bet will be to get out to the north-eastern tip of Neck Point Park. From there, the Moon should rise just left of the tip of Gabriola Island. If, on the other hand, you head over to Pipers Lagoon, you should see the Blue Moon rising from just behind the tip of Gabriola – still a very pretty sight.

Now, the Moon probably won’t look “blue” – it’s simply called a “Blue Moon” because it is the second full Moon this month.

The first full Moon was on July 1st, and since the lunar cycle is 29.5 days long, we’ve ended up with another full Moon today.

What are the odds?

“It was a million to one chance, doc… a million to one…”

Unlike some astronomical events, the odds of a Blue Moon happening are pretty easy to calculate, and it’s certainly not a million-to-one event…

The Lunar cycle is exactly 29.53 days, which is why it’s possible that we can get two full Moons in a month – well, any month except February. Yup, even in a leap year, February comes up a little short – arriving with a maximum 29 days – just half a day short of the Lunar cycle!

So, what are the odds of getting two full Moons in a given month? Well, it’s a little more likely for months with 31 days; a little less likely for 30-day months; and impossible for February. When you average it all out it’s a little over a 3% chance, or about once every 33 months.

I guess that once every 33 months is uncommon enough to justify the popular saying “Once in a Blue Moon”.

Now for a little Astronomy…

I can’t resist tossing a bit of extra astronomy in here, since I love it so much… 🙂

As I mentioned above, the Moon’s “cycle” is 29.53 days. But, Wikipedia, or any first-year astronomy textbook, will tell you that the Moon takes 27.3 days to complete one “orbit” around the Earth. So, what gives with the 29.53 number?  Well, the Moon is not the only thing in motion around here. The fact that the Earth orbits around the Sun once a year (taking the Moon along with it) means that the time between full Moons gets delayed – by a little over two days each cycle. (The  Moon is “full” when the side facing the earth is fully illuminated by the Sun… but, due to the orbital motion of the Earth, it takes a couple of extra days for the Moon to “swing around” far enough in its orbit for the Sun’s light to hit it face-on again.)

The “exact” time the Moon turned full was at 3:42am this morning, so the Moon will be a little “past full” when it rises this evening at 8:55pm, but don’t let that little detail spoil your fun… in fact, see if you can notice if the Moon is a tiny bit “out of round” due to the fact it’s a few hours past full…

In any case, it looks like it will be a great evening to check out Nanaimo’s Blue Moon!

Blue Moon for Nanaimo