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Tuesday, June 18, 2013


The Sky This Week - Thursday June 20 to Thursday June 27

Earth is at solstice on Friday June 21. The Full Moon is Sunday June 23. At this time it will be closer to Earth than any other time this year (a so called "Super Moon"). Mars rises in the morning twilight. Venus and Mercury are close together in the evening twilight. Saturn is high in the evening skies. The Moon occults the bright star alpha Librae 2 on the 20th.

The Full Moon is Sunday June 23. At this time the Moon will be at perigee, when it is closest to the Earth. This is the closest perigee for 2013 at 356989 km. A full Moon at perigee has been called a "SuperMoon", this is not an astronomical term, but an astrological one. While the Moon is close, it will have no real effect (or be distinguishable without a telescope and a good memory).

The Moon at Perigee and apogee as seen through a telescope. With the unaided eye, the Moon only appears half a finger-width wide, so the difference is much harder to see.

This months Full Moon could appear up to 14% bigger and 30% brighter in the sky than average. But will you actually notice if it is different to the last Full Moon? The limit of distances that someone with good vision can distinguish between is 1 minute of arc (about the width of a human hair). So, for the vast majority of people any difference smaller than 1 minute of arc cannot be seen.

The Moon this Full Moon will be 33'57" wide (just a touch over half a degree, around half a finger-width wide), last months Full Moon (358374 km) was 33'47" wide. Without a telescope and careful astrophotography you will not notice the difference.

If you can wait until January the 16th 2014, when the Full Moon is at Apogee, then it’s diameter will be 29'32" , and you could notice a difference if you have a good memory, but it won’t be spectacular. The illustration above is from November 28, 2012, when the Moon was at apogee and  29'33" wide when it was 406364 km from Earth

However, while the "SuperMoon" will not be spectacular, it will be a good photo opportunity, if you have a decent zoom on your camera, taking a photo of the Moon on June 23 and then again on January 16 2014 you will see a decent difference (you need to use exactly the same zoom enlargement, see Inconstant Moon for instructions).

The evening sky facing east in Sydney on June 20 at 5:05 pm AEST showing the waxing Moon just about to cover alpha2 Librae. (similar views will be seen from other locations at a similar local time eg 5:08 AEST Canberra). The inset shows a telescopic view of the Moon at 5:05 pm AEST, with alpha2 Librae about to go behind the Moon.

The waxing Moon passes in front of the bright alpha2 Librae in the constellation of Libra on the evening of June 20. Alpha2 Librae is a bright white star readily visible to the unaided eye (magnitude 2.8). The occultation will be seen from eastern Australia and South Australia. Everywhere else will see a nice, close approach.

From Adelaide the star reappears from the bright limb at 17:23 ACST. From Brisbane the star reappears at 18:05 AEST (the disappearance behind the dark limb is too deep in the twilight to be really seen).

From Canberra the star disappears behind the dark limb of the Moon at 17:08 AEST, and reappears at 18:08 AEST. From Hobart the star disappears behind the dark limb of the Moon at 17:28 AEST, and reappears at 18:07 AEST.

From Melbourne the star disappears behind the dark limb of the Moon at 17:13 AEST, and reappears at 18:03 AEST. From Sydney the star disappears behind the dark limb of the Moon at 17:06 AEST, and reappears at 18:10 AEST.

With the Moon not far from Full, this event is really best seen with binoculars or a small telescope (especially for the reappearance of the star on the bright limb of the Moon). If you have a tripod or other stand for your binoculars, it will be much easier to observe. Set up about half an hour before the occultation to watch the star dissapear (so you are not mucking around with equipment at the last moment).

Evening sky looking west as seen from Adelaide at 18:00 pm local time on Friday June 21. Venus and Mercury are closest at this time. Similar views will be seen elsewhere at the equivalent local times.  Click to embiggen.

Venus and Mercury come close together this week. From the 20th-23rd they are no further than two finger-widths from each other. On the 21st they are closest, being only a finger-width apart.

Jupiter is lost in the twilight, it is in conjunction with the Sun on June 20.  

Mercury  is visible above Venus but slowly lowers towards the horizon.

Venus  climbs higher in the evening twilight, and catches up to Mercury this week. It is now reasonably easy easier to see up to an hour and a half after sunset.

Saturn is easily visible above the eastern horizon in the early evening in the constellation of Libra. By 10 pm local time it is high above the northern-western horizon and very easy to see.This is an excellent time to view this planet in a small telescope, as there will be the little interference from horizon murk and air turbulence (and you can show the kids before they go to bed). By the end of the week Saturn is half a finger-width from the dim star Kappa Virginis.

Saturn, Arcturus and Spica from a broad triangle above the northern-western horizon.

Opposition (when Saturn is biggest and brightest as seen from Earth) was on April 28. However, Saturn will be a worthwhile evening target for telescopes of any size for several months. The sight of this ringed world is always amazing.

Morning sky on Sunday June 23 looking north-east as seen from Adelaide at 6:45 am local time in South Australia. Mars is below the red star Aldebaran in the twilight. Similar views will be seen elsewhere at the equivalent local time (click to embiggen).

Mars rises in the twilight, but will still be hard to see unless you have a flat, clear horizon. It forms a triangle with two red giant stars, Aldebaran and Betelgeuse.

There are lots of interesting things in the sky to view with a telescope. Especially with Saturn so prominent in the sky.  If you don't have a telescope, now is a good time to visit one of your local astronomical societies open nights or the local planetariums. Especially during the school holidays.

Printable PDF maps of the Eastern sky at 10 pm AEST, Western sky at 10 pm AEST. For further details and more information on what's up in the sky, see Southern Skywatch.

Cloud cover predictions can be found at SkippySky.


Well I was actually able to figure out my little telescope and the eye pieces and had a look at Saturn, before the clouds came in.
Regarding that 'no earthquake' with the Super moon thing you said on the previous post....we had a 2.2 rattle in Lilydale, Vic on June 21st.

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