Total Lunar Eclipse
Sunday evening September 27

A significant astronomical event will take place during the evening hours this Sunday, September 27, when Edmonton skies will be graced by a total eclipse of the Moon. A lunar eclipse is one of the most accessible astronomical events, visible to the naked eye, or through the lens of binoculars, telescope, or camera.

20150927_total_lunar_eclipse

Each phase of a lunar eclipse can last an hour or so, since it takes the Moon roughly that long to move its own diameter against the sky; totality can last somewhat longer due to the substantial size of Earth’s umbral shadow at the Moon’s distance. In this case the “total” phase of the eclipse will last 72 minutes, from 8:11 to 9:23 pm MDT.

One place to view this event is at the Public Observatory at TELUS World of Science – Edmonton and the adjoining meadow in Coronation Park where additional private telescopes will be set up by members of Edmonton RASC, which also provides the lion’s share of volunteer interpreters inside the Observatory. Weather conditions permitting, the facility will be open for its normal Sunday evening shift from 7-10 pm and through to the end of the partial phases. The Public Observatory at TELUS World of Science is open to everyone, free of charge.

The University of Alberta Observatory (5th Floor, CCIS Building) will also be open from 9:00 – 9:30 pm for students and public to observe the last part of totality. The Moon will be blocked from view by other campus buildings for the earlier portion of the event.

Here’s the full sequence of events as seen from Edmonton:

19:16 (7:16 pm) Moon rises due east, already partially eclipsed
20:11 Total eclipse begins
20:47 Mid-totality
21:23 Totality ends
22: 27 Partial eclipse ends
~22:45 Penumbral shading may be still be perceptible
23:22 Penumbral phase ends

The eclipse can be observed from anywhere on the night side of Earth where clear skies prevail. Observers specific to Edmonton and the Capital Region will need an unobstructed eastern horizon to see the opening act of the eclipse, but the Moon will continue rising into the southeastern sky throughout the evening hours.

This month’s Full Moon is special for a few reasons:

  • Firstly, the eclipse itself. Total eclipses occur less than once per year on average, despite there being a Full Moon every month. Usually the Moon with its tilted orbit passes well above or below Earth’s shadow. But a couple of times per year our satellite will be passing through the Sun-Earth plane — the aptly-named “ecliptic” — just when it’s aligned with the two. If that moon is new, an eclipse of the Sun may occur; if its full, it is the Moon itself which is eclipsed. Often just a fraction of the Moon passes through Earth’s umbral shadow, but in a total eclipse the entire Moon is immersed in that primary shadow. At such times it no longer reflects direct sunlight as Earth is in the way, however, our planet’s atmosphere acts as a lens that refracts sunlight forward. This is preferentially red light, for the same reasons that our sunrises or sunsets are primarily red. Thus the fully eclipsed Moon – the so-called “Blood Moon” — generally appears red or ruddy. Actual shading varies from one eclipse to the next due to different conditions within Earth’s atmosphere.
  • The Moon will be near its closest point to the Earth during the eclipse, the so-called “SuperMoon” or as we astronomers call it, the “perigean Full Moon”. Such events happen routinely every 14 lunations (lunar months), and have real effects – for example there will be especially high and low tides at this month’s Full Moon. At such times the Moon also appears bigger than usual, and brighter – or would be if it wasn’t eclipsed!
  • It so happens that this month’s Full Moon is the “Harvest Moon”, the most famous of the named moons that cycle through the calendar each year. The geometry of the Harvest Moon provides many consecutive days of favourable moonlit conditions in the evening hours for farmers harvesting their crops.

In each case, the lore surrounding the Blood Moon, the SuperMoon, or the Harvest Moon has a basis in science. None of them is uncommon: in the 21st Century there are 86 Total Lunar Eclipses, 89 (full) SuperMoons and 100 Harvest Moons. However, the odds of all happening at once are remote. The expected rate is fewer than one “Blood-Harvest-SuperMoon” per century, and in fact the upcoming event is the only one that will occur in the period 2000-2099. So don’t miss it!