Half an eclipse for early risers
OK - this one is for those viewing the total eclipse of the moon August 28 locally. Times and conditions are geared to Westport, MA - or very generally, the East Coast.
There can be a big gap between total lunar eclipses and there can be pretty small ones. Earth experienced a total lunar eclipse March 3, 2007. We get another one August 28, and still another February 20, 2008. But before the March 3rd event you had to go back to October 28, 2004, to see a total eclipse. So there had been nearly two-and-a-half years without an eclipse before the March 3rd event and for us, that one was obscured much of the time by clouds.
Like the August 28th event, here on the East Coast we got to see only half the show even if the skies were clear. (In Europe they had a much better view.) The total eclipse August 28th is a similar show, but instead of taking place in the evening, it takes place in the morning, which doesn't appeal to everyone.
So while the August 28th eclipse favors the West Coast, we will be able to see some of it, and if you care to get up early on the morning of Tuesday, August 28th, and if it's clear, and if you have chosen a location with a clear western horizon, here is the sequence of events you can expect to see:
4 am If youre up at this hour to see at least part of the lunar eclipse, why not start by turning a telescope on Mars? It will be half-way up the sky in the East, shining about as bright as Vega. It' still quite far away from us, so its disk will be less than one fourth the size of Jupiter, but still a worthy target.
4:20 am Moon 17 degrees high and at azimuth 237 degrees (wsw) begins to enter the penumbra of the Earth's shadow. This is a subtle part of the event because the penumbra is the lighter part of the shadow. Essentially you will be looking at a full moon, but the top of it will start to darken. (Yes, the top. While the moon will appear to be moving west setting because of the rotation of the Earth, it has its own eastward movement rotation around the Earth that is taking it into the Earth's shadow at this point. Actually, this counter-intuitive movement of the Moon is fascinating and sometimes fools even experienced observers. )
4:51 am Moon is about 12 degrees above the horizon now and should be starting to enter the Earth's umbra the darkest part of the shadow. It will be interesting to see exactly how noticeable the penumbral shading has been because at this stage the sky in the East will be quite light and the dimmer stars will have faded. While I am using precise times, to the eye the event does not move with this kind of precision- what you will notice is the moon is getting darker and darker, especially near the top edge.
5:06 am Venus, at azimuth 79 degrees, is rising a bit north of east. Since it is at magnitude 4.2 and will still show a crescent phase it may be visible between now and Sunrise. So if the eastern horizon is clear it will be worth checking your gaze in that direction and seeing if you can see Venus. Do be careful of the Sun. As we get near sunrise do NOT look for Venus near the horizon with binoculars or telescopes as you may catch a glimpse of the Sun instead which will damage your eyes. Remember that the time of Sun rise varies by several minutes depending on your exact location.
5:52 am - Total eclipse begins. At this point the moon is barely 2 degrees above the horizon at azimuth 254 degrees. The sky is nearly totally light. I doubt that any stars will be visible, but Venus will be almost 8 degrees above the horizon by now and may well be visible to the naked eye. Again, do not look for it with binoculars or telescopes this close to sunrise.
6:06 am The totally eclipsed moon is setting in the west; the Sun is rising in the east.
This is exactly the opposite of what we saw last March 3rd when a totally eclipsed Moon rose in the east shortly after the Sun set in the west. In that case the Moon was more than halfway through its total phase, so we saw a slow unveiling as the skies got darker, part of the moon grew brighter as it left Earth's shadow.
In both cases, however, we get to see (or got to see) only half of a lunar eclipse and that near the horizon where clouds may obscure it. So I think the eclipse of February 20, 2008 will be a more exciting and satisfying event. A little chilly, perhaps, but with that one we get to see the entire sequence of events from roughly 8 pm to midnight, a time that is more suitable to most people.
For detail on that winter event, go here: http://tinyurl.com/2cgawu