A total lunar eclipse will, weather permitting, be seen on Saturday evening, 4 April with Tasmanians well located to obtain a good view.
The event will be visible in its entirety from here and from all over Australia but at only five minutes long, totality will be very short indeed. Indeed, it is the shortest period of totality for a lunar eclipse since the year 1529!
A lunar eclipse occurs when the Moon moves through the Earth’s shadow in space. An eclipse does not occur every month, because the Moon’s orbit is tilted with respect to the Earth’s orbit around the Sun, and so it usually misses the shadow.
I saw my first total lunar eclipse when I was growing up in Sandy Bay, a Hobart suburb. I can remember sitting on the lawn with a school friend and watching the Moon turn a deep red colour. It was very impressive!
The Moon is a reddish colour even when it is completely within the Earth’s shadow because some sunlight is bent in the Earth’s atmosphere and falls within the shadow cone onto the Moon. Less blue light than red passes through, leaving an obvious red colour.
It is completely safe to watch lunar eclipses, because they do not involve looking at the Sun. Binoculars offer an excellent view and I recommend doing this especially during the partial phases of the eclipse, to see more clearly the curvature of the Earth’s shadow.
The event begins at 9:16pm (Daylight Saving Time), when the full Moon will start to move into the main part of the Earth’s shadow. By 10:58pm, the Moon will be entirely within the shadow, but it will remain completely engulfed only until 11:03pm.
Because the Moon will be just grazing the shadow’s inner edge, defining the exact beginning and end of totality is difficult. For this event the quoted duration is anything from 5 to 12 minutes. So the Moon will be a beautiful sight through the main five-minute period and for a few minutes before and after, changing little in appearance through that time.
Although during some total lunar eclipses, the Moon becomes so dark that it is hard to see at all, for this event it is expected to remain very easy to see and more orange-red than deep red because the Moon will be so close to the interior edge of the Earth’s shadow.
After totality, the Moon will gradually once again become bathed in sunlight, and by 12:45am, it will appear as a normal, bright full Moon.
The next total lunar eclipse visible from Tasmania will not occur until 2018.
Martin George, QVMAG Planetarium Manager