Tag Archives: moon

“The Dark Side of the Moon” – What happened to the moon last Sunday?

Last Sunday, half of the world bore witness to a rare event that had not occurred in over 30 years, and will not occur again for more than 15. Two fairly common events coincided on the same night: a lunar eclipse and a “supermoon”.

For  civilizations living centuries before us without technology like telescopes to help explain why, the sight of a lunar eclipse inspired many interesting theories to try to explain the frightening but captivating occurrence. These stories often involved some sort of celestial conflict or consumption of the Moon. Nevertheless, our faithful heavenly body never failed to rise again on the following night.


Progression of the “supermoon eclipse” on September 27, 2015. Source: Peter Martin Jørgensen from flickr.

Today, we know that a lunar eclipse, also eerily known as a “blood moon” for its red colour, happens when the Moon is in the shadow of the Earth. The Moon itself does not generate its own light like the Sun does, but rather, reflects the Sun’s light. During an eclipse, the Earth is between the Sun and the Moon, preventing the Sun from fully illuminating the Moon. The reddish tinge is a result of certain wavelengths of the visible light being scattered by the Earth’s atmosphere, much like why a sunset appears red.

There are two types of lunar eclipses: penumbral and umbral. How illuminated the Moon is during an eclipse depends on what part of Earth’s shadow its orbit crosses. An umbral lunar eclipse occurs when the Moon crosses into the Earth’s inner shadow, or umbra. These eclipses do not allow much light to reach the Moon. On the other hand, penumbral lunar eclipses occur when the Moon crosses into the Earth’s wider, outer shadow, called the penumbra. Penumbral lunar eclipses are less noticeable than umbral ones, but are more common, happening several times a year.

Geometry of a lunar eclipse. Source: User Sagredo from Wikipedia Commons.


Just like how the Earth’s orbit is not a perfect circle with the Sun exactly in the centre, the Moon’s orbit is elliptical and slightly off centre. This means that at any given point in the Moon’s orbit, the distance between the two bodies varies. When the Moon is at the farthest point from the Earth, it is called the apogee. At this point, the Moon will appear smaller than usual. Conversely, the point at which the Moon is closest to the Earth is called the perigee. Colloquially known as a “supermoon”, the Moon will appear to be larger than usual. Supermoons occur four to six times a year.

Lunar perigee and apogee. Source: User Tomruen from Wikipedia Commons.

Did you miss it? Fear not: here’s a time lapse of the event from the Associated Press.

YouTube Preview Image


While these celestial events no longer inspire the fear that our ancestors felt, the sense of wonder and awe still remains. The next supermoon eclipse won’t be until the year 2033. Until then, mark your calendars!

– Trevor Tsang


Bloodmoon: What the-?! When the-? How the-?!


The supermoon rises behind Glastonbury Tor (Photo: Matt Cardy / Getty, taken from The Telegraph)

Did you see the bloody moon last Sunday, September 27? If not, then too bad because the next time you see it will be in 18 years!

You may be wondering what exactly this “bloody moon” is and why it is such rare occurrence. Let me get down to the basics.

First of all, a lunar eclipse occurs when the Earth blocks the sunlight reflecting off of the moon’s surface, creating a shadow against the moon and darkening it. There are three types of lunar eclipses (penumbral, partial and total) but for now, we are interested only in a total lunar eclipse when the moon “bleeds” against the dark sky. In actuality, the full moon gets covered completely by the Earth’s shadow, when the moon, Earth and Sun are in perfect alignment. It turns a reddish hue from some light refracted off of Earth’s atmosphere towards the moon.

Image taken from Wikipedia, labeled for non-commercial reuse.

Even though we have a full moon every month, total lunar eclipses only happen once every 6 months or so. A 5-degree angled orbit of the moon around the Earth makes the occurrence less likely to happen.

On the other hand, a supermoon can be seen when a full moon is at its perigee, or in other words, at the closest point in the moon’s orbit relative to Earth. At this perigee, the moon appears brighter and bigger by 12-14% than a moon at the apogee, a very noticeable change.

Moon size and position at perigee and apogee. (Image taken from skynews.ca)

According to EarthySky.org, the next supermoon will happen in November, 2016 then January, 2018, so roughly every 13 months.

The effect of a total lunar eclipse occurring at the Earth’s perigee is an abnormally large, very photogenic, “super bloodmoon”. The rarity of this cosmic happenstance is roughly once every 18 years. The closest, biggest and reddest supermoon since 1982 occurred in September 27/28 2015. It is visible to North and South America, Europe, Africa, and parts of Asia- in short, we can see it from Canada. Luckily for me, I stepped out of my house that evening to witness the eclipse as it was occurring at around 10 PM PST. No sunglasses needed, and no telescopes either. Just a blanket, a folding chair and some mosquito repellent then I was good to go! For all of you who missed it though and would like to re-watch it, a recording from Griffith Observatory, CA is included here.

YouTube Preview Image