I took this image of the Solstice Sunset near my home in the UK last year, it was an amazing experience watching the sun sink below the horizon on the longest day.
Will we be lucky enough to be able to witness this wonder again this year and see some more great images?
Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)
Tonight (actually around 0130 tomorrow morning) the Full Moon will reach its highest point due south, just an hour and a half after the eclipse ends. Despite being at its highest in the sky, you’ll still struggle to see it, as it is very low down. In fact the Full Moon nearest the Summer Solstice is the lowest Full Moon of the Year
First, let’s begin with the definition of “Full Moon”. A Full Moon occurs when the Moon is diametrically opposite the Sun, as seen from the Earth. In this configuration, the entire lit hemisphere of the Moon’s surface is visible from Earth, which is what makes it “Full”. There is an actual instant of the exactly Full Moon, that is the exact instant that the Moon is directly opposite the Sun. Therefore when you see timings listed for the Full Moon they will usually include the exact time (hh:mm) that the Moon is 180° round from the Sun (we call this point opposition). Here’s a list of the times of all Full Moons between June 2011 and June 2012:
| Month | Date of Full Moon | Time of Full Moon (UT) |
| June 2011 | 15 June | 2014* |
| July 2011 | 15 July | 0640* |
| August 2011 | 13 August | 1857* |
| September 2011 | 12 September | 0927* |
| October 2011 | 12 October | 0206* |
| November 2011 | 10 November | 2016 |
| December 2011 | 10 December | 1436 |
| January 2012 | 09 January | 0730 |
| February 2012 | 07 February | 2154 |
| March 2012 | 08 March | 0939 |
| April 2012 | 06 April | 1919* |
| May 2012 | 06 May | 0335* |
| June 2012 | 04 June | 1112* |
* UK observers should add on one hour for BST As you can see from this table, the instant of the Full Moon can occur at any time of day, even in the daytime when the Moon is below the horizon. So most often when we see a “Full Moon” in the sky it is not exactly full, it is a little bit less than full, being a few hours ahead or behind the instant of the Full Moon. I’ll refer to this with “” marks, to distinguish this from the instant of the Full Moon (they look virtually identical in the sky). The Moon rises and sets, like the Sun does, rising towards the east and setting towards the west, reaching its highest point due south around midnight (although not exactly at midnight, just like the Sun does not usually reach its highest point exactly at noon). And like with the Sun the maximum distance above the horizon of the “Full Moon” varies over the year. The Sun is at its highest due south around noon on the Summer Solstice (20 or 21 June) and at its lowest due south around noon on the Winter Solstice (21 or 22 Dec) (of course the Sun is often lower than this, as it rises and sets, but we’re talking here about the lowest high point at mid-day, i.e. the day of the year in which, when the Sun is at its highest point that day, that height is lowest…) And because Full Moons occur when the Moon is directly opposite the Sun, you can imagine the Moon and Sun as sitting on either sides of a celestial see-saw: on the day when the Sun is highest in the middle of the day (in Summer), the Moon is at its lowest high point at midnight; and on the day when the Sun is at its lowest high point in the middle of the day (in Winter), the Moon is at its highest high point at midnight. This means, in practical terms, that Summer “Full Moons” are always very low on the horizon, while Winter “Full Moons” can be very high overhead. Here’s a table of the altitude of the “Full Moon” when due south. Remember the times in this table don’t match the exact time of the Full Moon, but instead have been chosen as the closest in time to that instant, and so have be labelled “Full Moon” (in quotes).
| Month | Date of Full Moon | Time of Full Moon (UT) | Time/Date of “Full Moon” due S | Time from/since instant of Full Moon | Altitude due S (degrees)** |
| June 2011 | 15 June | 2014* | 0127BST 16 June 2011 | +4h13m | 10° 05′ |
| July 2011 | 15 July | 0640* | 0012BST 15 July 2011 | -7h28m | 10° 24′ |
| August 2011 | 13 August | 1857* | 0126BST 14 August 2011 | +5h27m | 19° 19′ |
| September 2011 | 12 September | 0927* | 0049BST 12 September 2011 | -9h38m | 31° 49′ |
| October 2011 | 12 October | 0206* | 0053BST 12 October 2011 | -1h13m | 44° 16′ |
| November 2011 | 10 November | 2016 | 0005GMT 11 November 2011 | -3h49m | 53° 24′ |
| December 2011 | 10 December | 1436 | 0030GMT 11 December 2011 | +9h54m | 56° 03′ |
| January 2012 | 09 January | 0730 | 0006GMT 09 January 2012 | -7h24m | 53° 36′ |
| February 2012 | 07 February | 2154 | 0031GMT 08 February 2012 | +2h37m | 43° 47′ |
| March 2012 | 08 March | 0939 | 0000GMT 08 March 2012 | -9h39m | 35° 37′ |
| April 2012 | 06 April | 1919* | 0145BST 07 April 2012 | +5h26m | 21° 45′ |
| May 2012 | 06 May | 0335* | 0102BST 06 May 2012 | -3h33m | 15° 20′ |
| June 2012 | 04 June | 1112* | 0047BST 04 June 2012 | -11h25m | 11° 49′ |
* UK observers should add on one hour for BST ** The altitude here is based on my observing location in Glasgow, Scotland. You can find out how to work out how high these altitudes are here. As you can see from this table, the highest “Full Moon” due S this year occurs at 0030 on 11 December 2011, when the Moon will be over 56° above the southern horizon (approximately the height of the midsummer mid-day Sun which culminates at 57°34′). Compare this to the “Full Moon” this month, just after the eclipse, in the morning of 16 June, when the Moon barely grazes 10° above the horizon, and you can see just how low the midsummer Full Moon can be. In fact the closeness of summer “Full Moons” to the horizon means that this is an ideal time of year to try and observe the Moon Illusion.
Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)
Today, 13 June, is one of only four days in the year when the time as read on a sundial will be exactly correct.
Sundials usually tell the time using the shadow of the gnomon as cast by the Sun. This is possible as the Sun appears to move across the sky at an approximately constant speed, and so the shadow of the gnomon also moves at an approximately constant speed. The inconstancy of the Sun’s apparent motion in the sky – and therefore of the gnomon’s shadow on a sundial – is the subject of this article, and is calculated using the Equation of Time.
If you look at the shadow of a sundial’s gnomon it will fall onto a curve of numbers, along hour lines indicating local solar time. This is not equal to the official clock time until three important corrections are made:
Please read the rest of this article on Dark Sky Diary
Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)
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).
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.
Please read the rest of this article on Dark Sky Diary
Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)
Over the next couple of months ESA’s Cluster spacecraft are going to get very close to Earth, with the orbit of one of the four satellites dropping as low as 200-300km from the Earth’s surface. This is low enough that you may indeed be able to spot – and if you’re skilled enough, take pictures of – the spacecraft.
ESA's Cluster Spacecraft
The four satellites – named Rumba, Salsa, Samba and Tango – were launched in 2000 to study the interaction between the Earth’s magnetic field and the Sun’s solar wind, and because there are four of these satellites, orbiting Earth in a tetrahedral configuration (i.e. one satellite at each of the apexes of a triangular pyramid) the Earth’s magnetosphere can be mapped in 3D.
The solar wind interacts with the Earth's magnetosphere
During June and July 2011 one of the Satellites, Cluster II (Salsa), will come within 200-300km of the surface of the Earth, which means there is a chance you might see it.
They might not be visible from the UK – in fact the British Astronomical Association suggest that the best chance of seeing these satellites is from latitude 20-30 N, so for anyone holidaying in the Canary Islands this summer there’s a chance you’ll catch a glimpse. There is a chance they’ll be visible further north too, from Europe. In any event, the brightness of the satellites is unknown at this stage, and so we can’t tell how easy it will be to spot, even if it’s visible from where you are.
The best way of checking whether the satellites are visible from where you are is to use the excellent Heavens Above website. Enter your observing location and then under “Satellites” click “select another satellite”, then in the “Satellite Name” box type “Cluster%” (the % is important). You can then select each of the four Cluster satellites and in the upper right corner of the information panel you can click “Passes (visible)” to see if there are any passes worth watching for from your location.
This will give you five crucial bits of information:
ESA have even announced a competition on Facebook, where they are encouraging people to try and image the satellites! This is no mean feat, but not without precedent. In fact a number of very experienced astrophotographers have caught images of the International Space Station as it orbits about 360km overhead. One of my favourites is this one by Thierry Legault, of the space shuttle Atlantis approaching the International Space Station where both were silhouetted in front of the Sun.
Thierry Legault's incredible image of Atlantis and the ISS taken from Earth
Happy satellites hunting, and let me know if you catch a glimpse!
(HT to the BAA for bringing this to my attention).
