June Night Sky Wonders

What can you see in the June night sky? During the month of June there is precious little darkness. Nevertheless there’s plenty to see and ponder on in the night sky. There has just been a lunar eclipse, it is summer solstice time and also the time of year to look out for clouds (not any old cloud but a very special kind). And of course there are some wonderful constellations on view.

There was a lunar eclipse on June 15.  Observers in Africa, southern Asia and Australia witnessed a total lunar eclipse. Total lunar eclipses must occur on the date of a full moon and June’s Full Moon was on the 15^th(every month’s full Moon has its own pet name and June’s is traditionally known as the Strawberry Moon, probably because it is strawberry season, yum yum). A total lunar eclipse occurs when Earth is between the Moon and the Sun, blocking the Sun’s light from reaching the Moon. The reddish, coppery-brown colour typical during a total eclipse of the Moon is due to indirect sunlight which is filtered as it passes through the Earth’s atmosphere.

June 21 marks the day when the Sun will reach its northernmost position in the sky and will be directly over the Tropic of Cancer at 23.44 degrees north latitude. This is the first day of summer (summer solstice) in the northern hemisphere and the first day of winter (winter solstice) in the southern hemisphere.

Clouds are not usually associated with observing but now is the time to look out for the ‘night shinning’ clouds of the evening twilight known as noctilucent clouds (NLC’s).  The best time to look out for these spectacular sights is one or two hours after sunset, and also one to two hours before sunrise. Look towards the northwest horizon to see this rare and beautiful phenomenon.  If you are in luck this is what you should  see.

The cause of this unpredictable celestial treat is not fully understood and is a relatively recent celestial phenomena.  NCL’s are very high clouds which are located in the mesosphere at altitudes of around 80Km (50 miles) and are composed of tiny crystals of water ice. They were first observed in 1885 by an amateur astronomer two years after the eruption of Krakatoa . For this reason their formation was associated with volcanic ash but this idea has been abandoned as an explanation.

Ordinary clouds form when water collects on particles in the atmosphere, but NCL’s may form directly from water vapour in addition to forming on dust particles. The source of both the dust and the water vapour is a bit of a mystery, or at least a cause for debate.  The most likely source of dust is possibly space, micro meteoroids being just ideal to seed noctilucent clouds. The water vapour is the result of upwelling winds in the summertime carrying water vapour from the moist lower atmosphere toward the mesosphere and this is why NLC’s appear during summer. Another source of water may be the vapour released from the Space Shuttle exhaust and other spacecraft which is mainly water.

NASA has been studying NCL’s for some time and are trying to determine if there is a relationship between climate change and these wonders of the night sky. The Aeronomy of Ice in the Mesosphere satellite, (AIM), is monitoring the make up and formation of these amazing clouds which are known as Polar Mesospheric Clouds  (PMC’s) when observed from space.

Data returned from AIM showing Polar Mesospheric Clouds over the Arctic. (Image credit: NASA)

For more information on this mission click on the link http://aim.hamptonu.edu/

Leo disappearing behind the tree before he sinks below the horizon and out of view for the summer. (Image credit: Armagh Planetarium)

It is really midnight before there is darkness at this time of year. We can see Leo sinking below the horizon in the West, paw first. To the left of Leo is the large sprawling but faint constellation of Virgo sporting the bright star Spica , not to be confused with Saturn which is located in the goddess of corn and agriculture at the moment. Saturn takes nearly 30 years to orbit the Sun so it spends an average of two years in each of the zodiacal constellations. Saturn is the bright object closest to Leo. Spica and Saturn actually form a triangle with the bright orangish star Arcturus which is higher in the sky.

At the feet of Virgo and low in the southern horizon you will find another zodiacal constellation, Libra, the only one represented by an inanimate object, a set of scales. Given dark, clear skies and an unobstructed view the shape of a pair of scales on its side can be made out. The ancient Greeks saw the stars of Libra as part of Scorpius, specifically the scorpion’s claws. In fact the two brightest stars in Libra, named by ancient Arab astronomers, Zubenelgenubi (meaning southern claw) and Zubenelchemale ( meaning northern claw) testify to this past association.   The Romans separated these constellations returning to the Babylonian idea of associating the stars of Libra with a scales or balance reflecting the notion of the equal length of day and night.  Antares is the brightest star in Scorpius.  A huge supergiant star with a distinct reddish colour, its name means ‘rival of Mars’ as it resembles the Red Planet in our sky. This star is about 700 times the diameter of our Sun. It can be seen very low in the sky in the southeast.

Look South to see the stars of Ophichus which form what looks like the gable end of a large house. (Image Credit: Armagh Planetarium)

Still looking South but higher in the sky are the constellations of Ophiuchus, the Serpent Bearer, and Serpens, the snake he is hauling across the sky.  Serpens is the only constellation that is in two parts, Serpens Caput to the west of Ophiuchus and the tail of the snake, Serpens Cauda, trailing behind Ophiuchus.

The well known asterism of the Summer Triangle consisting of the three bright stars Deneb, Vega and Altair continues to rise higher in the sky in the southeast.  Deneb marks the tail of Cygnus the Swan which flies along the Milky Way with wings outstretched. It forms a distinctive cross in the heavens and is sometimes known as the  Northern Cross.  Deneb is one of the most luminous stars known but because it is so far away we see it as only the 20th brightest star in the sky.  If Deneb were as close to us as Sirius, which we see as the brightest star, then it would be as bright as the Moon and if it were as near as Alpha-Centauri, ( the closest star system to us, after the Sun)  we would be able to read the newspaper at midnight  with its light!

Mary Bulman, Education Support Officer

(Article by Mary Bulman)