Partial Lunar Eclipse on 17 August 2008

Eclipse time again…

This month, we are blessed with two eclipses: a total solar eclipse on August 1 and two weeks later on August 17, we have a partial lunar eclipse.

Solar eclipse happens when the Moon blocked the Sun and this only happens during new moon when the Moon is between us and the Sun. Lunar eclipse happens when the Moon moves into Earth’s shadow and “disappears” from view. This only happens during full moon when our planet is between the Moon and the Sun.

If that is the case, why do we not have eclipses every new moon and full moon? The answer lies in the orbit of the Earth and the Moon.

The orbit of the Moon around Earth is not in the same plane as the orbit of our Earth around the Sun (the ecliptic); the Moon’s orbit inclines about 5 degrees from the ecliptic. Because of that, the Sun-Earth-Moon is not always in a straight line; most of the time the Moon is either above or below the ecliptic. That’s why the Moon doesn’t block the Sun on every new moon or in Earth’s shadow every full moon.

Unlike a solar eclipse that is only visible along the narrow “path of totality”, a lunar eclipse can be viewed anywhere on the night side of Earth; meaning almost half the globe can see the event, and you can see it right outside your house provided it is night-time and the sky is clear.

Another difference is that for a total solar eclipse, the longest time the Sun can disappear from view is 7 min 40 sec, because the Moon and the Sun has almost the same angular size in the sky (the Sun although is 400 times larger than the Moon, it is also 400 times further away). After blocking the Sun briefly, the Moon will move away and reveal the Sun again.

But for a total lunar eclipse, the Moon can disappear from view as long as an hour. This is because Earth cast a shadow in space far larger area than the Moon itself and the Moon will require some time to move out from the shadow. Check this animation of the partial lunar eclipse at Shadow & Substance to visualise that.

Partial Lunar Eclipse on Sep2006. Click to enlarge

This weekend, instead of totally disappear into the shadow of our planet (a total lunar eclipse), the Moon will only partially goes into shadow, resulting in a partial lunar eclipse that lasts about 3 hours.

The show starts at 2:23 am (18:23 UT) when the Moon first contacts the Earth’s penumbra*. At 3:35 am (19:35 UT), the Moon is about to enter the umbra*. Little by little, the Moon will be “eaten-up” until it reaches its greatest eclipse at 5:10 am (21:10 UT), where 81% of the Moon will be immersed in the Earth’s shadow. After that the Moon will slowly “coming back” and at 6:44 am, the Moon will be totally out from the umbra. The eclipse will end at 7:57 am (23:57 UT) when the Moon leaves the penumbra.

This time, the eclipse favour Peninsular Malaysia. People from the peninsular will be able to see the Moon leaving the umbra. Unfortunately for Sabah and Sarawak, the Sun rises before the Moon is out from the umbra.

*Our Earth’s shadow consists of two parts: the darker central umbra and the lighter penumbra.

Click here for more details and diagram of the eclipse.

What will you see?

At the start of the eclipse, the Moon looks like a normal bright full Moon. Then as it enter the penumbra it seems to get just a little bit darker, but you won’t notice much, since the change is small.

As time goes by, you will start to see bit by bit of the Moon starts disappearing. At the greatest eclipse, the “dark part” of the Moon may change its colour to copper red or orange, depends on the condition of our atmosphere.

After that, the whole process reverses and the Moon gets lighter and lighter until it finally goes back to being a normal Full Moon.

How to view this partial lunar eclipse?
This event can be observed just outside your house. But you have to make sure that you an unobstructed western horizon – the Moon is setting as you view the event.

You can observe this event just by using the naked eyes. Alternatively you can also view it through binocular or telescope (no filter required). Or if you want to record the event, you can use a camera to take multiply shots of the eclipsed Moon throughout the event and then stitched them together to get the progress of the eclipse.

Hope you will enjoy the show this weekend and clear skies to everyone out there.


~ by thChieh on August 12, 2008.

2 Responses to “Partial Lunar Eclipse on 17 August 2008”

  1. […] Partial Lunar Eclipse on 17 August 2008 « My Dark Sky […]

  2. […] Lunar Eclipse on 17 August 2008 (Images1) So, as promised, below is the sequence of last weekend partial lunar eclipse with the Petronas Twin Tower and KL Tower (barely visible to the left) as foreground. […]

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