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Lunar Eclipse 28 September 2015: The Blood Supermoon

September 22, 2015 Leave a comment

Stargazers in the UK are ideally placed to see a rare astronomical event next week, a Total Lunar Eclipse. While not as dramatic as a Total Solar Eclipse, a lunar eclipse is well worth watching for, as the Moon turns deep red at totality.

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A Blood-red Lunar Eclipse

Unlike a Total Solar Eclipse, where totality lasts only a few minutes, a total eclipse of the Moon last several hours. In the morning hours of Monday 28 September the lunar eclipse begins at 0111BST and ends at 0622BST as the Moon sets. During the very early and late hours of the lunar eclipse you will see part of the full Moon’s disk darken, but it’s only when the Moon enters totality that it will turn red. This dramatic event will happen between 0311 and 0423BST.

This month’s lunar eclipse is made even rarer by the fact that the full Moon on 28 Sep is what’s called a Supermoon. This means that the Moon is closer than normal to Earth, and will appear slightly larger and brighter in the sky. But don’t believe the hype: it will be only a few % closer and so your eye will not be able to detect the difference between this Supermoon and any other Full Moon – except this time it’ll be blood red due to the eclipse! (The Moon may actually look bigger to you if you catch it low on the horizon, but that’s due to the Moon Illusion).

The brilliant XKCD sums up the Supermoon hype nicely

The brilliant XKCD sums up the Supermoon hype nicely

A lunar eclipse occurs when the Moon, in its orbit around the Earth, passes into the Earth’s shadow, as cast by the Sun. You might imagine that this would happen once every lunar orbit, or once a month. That it does not is due to the fact that the Moon’s orbit around the Earth is tilted by around 5 degrees compared with the Earth’s orbit around the Sun. So in most orbits the Moon passes above or below the Earth’s shadow.

However, once in a while (there are at least two lunar eclipses each year) the orbital planes will align so that the Moon passes through the Earth’s shadow, sometimes just grazing it, in which case we get a partial lunar eclipse, and at other times passing right through the shadow, when we get a total lunar eclipse.

The Earth’s shadow has two distinct regions, forming two concentric cones: the inner, darker, part of the shadow is called the umbra, and objects within this part of the shadow receive no direct light from the Sun. The outer, lighter, part of the shadow is called the penumbra, and objects within this part of the shadow can receive direct light from the Sun, but part of the Sun’s disk will be obscured by the Earth, and so less light than normal falls on the object.

There are several distinct phases of a lunar eclipse, as the Moon travels through the penumbra and umbra. For this lunar eclipse the total time during which the Moon is at least partially in the Earth’s shadow is 5 hours 11 minutes, and 72 minutes of this is spent entirely within the umbra, i.e. in total eclipse.

lunareclipse28sep

These phases are given the names: P1, the time when the Moon’s disk enter the penumbra; U1, the time when the Moon’s disk enters the umbra; U2, the time when the entirety of the Moon’s disk is within the umbra; U3, the last time when the entirety of the Moon’s disk is within the umbra; U4, the last time when part of the Moon’s disk is within the umbra; and P4, the last time when part of the Moon’s disk is within the penumbra.

The UK is ideally placed to view this total lunar eclipse, although you will have to stay up very late, or get up very early. The Moon is in the sky for the entirety of the eclipse. Observers in western Europe, NW Africa, E North America, and South America will all see the full eclipse from beginning to end.

eclipse28sep2

A detailed information sheet for this eclipse (and others) is available (pdf) on the NASA Eclipse website.

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Partial Lunar Eclipse Tonight, 25 April

April 25, 2013 Leave a comment

There’s a partial lunar eclipse tonight, visible from the UK, as well as from the rest of Europe, Africa, Asia and Australia.

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It won’t be hugely dramatic, as it’s only a partial eclipse of the Moon, not a total one. Even total lunar eclipses are far less grand than total solar eclipses, unfolding over several hours rather than minutes, and turning the Moon a deep red rather than making it vanish altogether.

And for partial lunar eclipses, like tonight’s, all we’ll see is a slight darkening of the edge of the Moon, what we call the “limb”.

Nevertheless it’s worth watching out for if you have clear skies. And the best thing of all is that light pollution isn’t really an issue; you’ll see it just fine from a city.

Here are the timings:

Penumbral Eclipse Begins: 18:03:38 UT
Partial Eclipse Begins: 19:54:08 UT
Greatest Eclipse: 20:07:30 UT
Partial Eclipse Ends: 20:21:02 UT
Penumbral Eclipse Ends: 22:11:26 UT

Remember that these times are in universal time (UT) which is the same as GMT, so add one hour on for BST.

Best time to look is between 9pm and 9:20pm BST.

Image from NASA’s eclipse site.

Lunar Eclipse December 2011

December 9, 2011 1 comment

On Saturday 10 December 2011 the Moon will enter total lunar eclipse between the hours of 1405 and 1457 GMT. The full eclipse process begins at 1131 and ends six hours later at 1731 GMT, but outwith the 52 minutes of total eclipse the moon will only be partially in the Earth’s shadow.

A lunar eclipse occurs when the Moon, in its orbit around the Earth, passes into the Earth’s shadow, as cast by the Sun. You might imagine that this would happen once every lunar orbit, or once a month. That it does not is due to the fact that the Moon’s orbit around the Earth is tilted by around 5 degrees compared with the Earth’s orbit around the Sun. So in most orbits the Moon passes above or below the Earth’s shadow.

However, once in a while (there are at least two lunar eclipses each year) the orbital planes will align so that the Moon passes through the Earth’s shadow, sometimes just grazing it, in which case we get a partial lunar eclipse, and at other times passing right through the shadow, when we get a total lunar eclipse.

The Earth’s shadow has two distinct regions, forming two concentric cones: the inner, darker, part of the shadow is called the umbra, and objects within this part of the shadow receive no direct light from the Sun. The outer, lighter, part of the shadow is called the penumbra, and objects within this part of the shadow can receive direct light from the Sun, but part of the Sun’s disk will be obscured by the Earth, and so less light than normal falls on the object.

There are several distinct phases of a lunar eclipse, as the Moon travels through the penumbra and umbra. For this lunar eclipse the total time during which the Moon is at least partially in the Earth’s shadow is 360 minutes, and 52 minutes of this is spent entirely within the umbra, i.e. in total eclipse.

The phases of the 10 Dec 2011 total lunar eclipse (via NASA's eclipse website)

These phases are given the names: P1, the time when the Moon’s disk enter the penumbra; U1, the time when the Moon’s disk enters the umbra; U2, the time when the entirety of the Moon’s disk is within the umbra; U3, the last time when the entirety of the Moon’s disk is within the umbra; U4, the last time when part of the Moon’s disk is within the umbra; and P4, the last time when part of the Moon’s disk is within the penumbra.

Unfortunately, the UK is far from ideally placed to view this total lunar eclipse. The Moon will rise some time around 1530 UT, well after U3 (the end of the total eclipse), and nearing U4 (the end of the partial eclipse). It may still be worth watching for the Moon rising in the east around 1530, but at least for UK observers a blood-red total eclipse Moon will not be seen.

A detailed information sheet for this eclipse (and others) is available (pdf) on the NASA Eclipse website.

Total Lunar Eclipse 15 June 2011

June 13, 2011 40 comments

The first total eclipse of the Moon of 2011 occurs this Wednesday evening, 15 June 2011, and it will be the longest lunar eclipse in over a decade. However the views from the UK (and Europe) will be constrained by the fact that the Moon will be below the horizon for much of the eclipse, and will rise fully eclipsed, or in some cases even coming out of eclipse. It’s still worth having a look though: just try to find somewhere with a very low and clear SE horizon, as this will be the direction in which the Moon will rise, and it will be in eclipse only while it is VERY low (only a few degrees above the horizon).

Lunar Eclipse, December 21, 2010, by Jiyang Chen

A lunar eclipse occurs when the Moon, in its orbit around the Earth, passes into the Earth’s shadow, as cast by the Sun. You might imagine that this would happen once every lunar orbit, or once a month. That it does not is due to the fact that the Moon’s orbit around the Earth is tilted by around 5 degrees compared with the Earth’s orbit around the Sun. So in most orbits the Moon passes above or below the Earth’s shadow.

However, once in a while (there are at least two lunar eclipses each year) the orbital planes will align so that the Moon passes through the Earth’s shadow, sometimes just grazing it, in which case we get a partial lunar eclipse, and at other times passing right through the shadow, when we get a total lunar eclipse.

The Earth’s shadow has two distinct regions, forming two concentric circles [correction, the shadow is two cones, not circles – need to think in 3D! (see comments)]: the inner, darker, part of the shadow is called the umbra, and objects within this part of the shadow receive no direct light from the Sun. The outer, lighter, part of the shadow is called the penumbra, and objects within this part of the shadow can receive direct light from the Sun, but part of the Sun’s disk will be obscured by the Earth, and so less light than normal falls on the object.

The umbra and the penumbra

For the lunar eclipse of 15 June 2011 the Moon will pass very deeply into the darker umbra, making this an especially dark – and long – eclipse.

There are several distinct phases of a lunar eclipse, as the Moon travels through the penumbra and umbra. For this lunar eclipse the total time during which the Moon is at least partially in the Earth’s shadow is 219 minutes, and 100 minutes of this is spent entirely within the umbra, i.e. in total eclipse.

The phases of the 15 June 2011 total lunar eclipse (via NASA's eclipse website)

These phases are given the names: P1, the time when the Moon’s disk enter the penumbra; U1, the time when the Moon’s disk enters the umbra; U2, the time when the entirety of the Moon’s disk is within the umbra; U3, the last time when the entirety of the Moon’s disk is within the umbra; U4, the last time when part of the Moon’s disk is within the umbra; and P4, the last time when part of the Moon’s disk is within the penumbra.

The timings for these instances are well known. In the following table are: the timings for P1, U1, U2, U3, U4, and P4; the time of greatest eclipse (i.e. where the Moon is closest to the centre of the umbra); and the local times of moonrise for a variety of places around the UK

Eclipse Contact Contact Description Time (UT) Time (BST) Moonrise Time (BST) (UK Location)
P1 Penumbral Eclipse Begins 17:24:34 UT 18:24
U1 Partial Eclipse Begins 18:22:56 UT 19:22
U2 Total Eclipse Begins 19:22:30 UT 20:22
Greatest Eclipse 20:12:37 UT 21:12 21:12 (Channel Islands)
21:14 (London)
21:26 (Cardiff)
21:33 (Manchester)
21:56 (Belfast)
21:58 (Glasgow)
U3 Total Eclipse Ends 21:02:42 UT 22:02
22:19 (Orkney)
21:23 (Shetland)
U4 Partial Eclipse Ends 22:02:15 UT  23:02
P4 Penumbral Eclipse Ends 23:00:45 UT  00:00

UT = Universal Time = GMT
BST = British Summer Time = GMT+1

As you can see, the UK is far from ideally placed to view this total lunar eclipse, but the further south and east you are the better your chances of seeing something. The Moon will rise well past U2 across the UK, and everywhere except the Channel Islands and SE England it will rise well past greatest eclipse. Indeed in the north of Scotland the Moon will rise after the total eclipse phase ends (i.e. past U3).

Observers in the Channel Islands and in the SE of England will have around 50 minutes of total eclipse to observe although the Moon will still only be a few degrees above the horizon at U3), and here in Glasgow I’ll have about 4 minutes between moonrise and U3!

While in total eclipse no direct sunlight will fall on the Moon, but we will still be able to see it illuminated a dull red colour. How can this be, if there is no sunlight shining on it to light it up? It is due to the fact that the Sun’s light is refracted, or bent, through the Earth’s atmosphere. The red light from the Sun’s spectrum is refracted the most, and so it is this light that will illuminate the Moon during a lunar eclipse. In effect, the light you will see on the Moon is the combined light from all the sunrises and sunsets on Earth, being focused onto the Moon by the lensing effect of the Earth’s atmosphere.

A detailed information sheet for this eclipse (and others) is available (pdf) on the NASA Eclipse website.

Total Lunar Eclipse on the Winter Solstice

December 19, 2010 1 comment

This Tuesday 21 December 2010 is the Winter Solstice, and in addition there will be a total lunar eclipse, occurring at sunrise in the UK.

Total Lunar Eclipse, image by Nick James

Total Lunar Eclipses occur when the Moon passes into the shadow of the Earth. That this does not happen every 29 days (the time it takes for the Moon to orbit the Earth) is due to the fact that the Moon’s plane of orbit is not the same as the Earth’s orbital plane around the Sun, and so the Moon passes above or below the cone of the Earth’s shadow most of the time. Every so often, however, these two planes align to create the conditions for a Lunar Eclipse.

When this happens, the Moon will begin to darken in the sky, eventually turning a dark red colour. Unlike a Solar Eclipse, where the Sun’s light is totally blocked out by the Moon, in a Lunar Eclipse the Moon is still visible.

Tuesday’s Lunar Eclipse will begin at 0528 GMT when the Moon enters the Penumbra, the outer part of the Earth’s shadow. This will begin a slight darkening of the Moon, the darkness extending across the Moon’s surface slowly, taking around an hour. At 0632 GMT the Moon will enter the central, darkest part of the Earth’s shadow, form which point it will darken appreciably until, at 0740 it will be in total eclipse, with the full face of the Moon darkened red. This will last until 0854 GMT, at which point the Moon will slowly begin to darken again.

At this point, however, the Moon will have set for some UK observers, or be very low in the sky, on the western horizon, as it is about to set. The time at which it finally sets depends on where you are. In London it sets at 0812 GMT, while in Glasgow (my home town) it sets at 0857 GMT, just minutes after total eclipse ends.

This means that observers in Scotland will have the best view, and the further north you are the more you’ll see.

This lunar eclipse also has the rare distinction of being one where you can see the eclipsed Moon and the Sun in the sky at the same time, as Sun rises around 11 or 12 minutes before the Moon sets, wherever you are in the UK.

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