Starguide: July

By Jenny Winder
 What to look out for in the July night sky

This month the sky is presided over by the magnificent Summer Triangle that comprises the stars Deneb in Cygnus, Lyra in Vega and Altair in Aquila.

The Moon will be full this month on July 3rd and new on July 19th. On July 15th the Moon will occult the planet Jupiter between 01:00 UT and 02:30UT. How close the occultation appears depends on your location. For the Southeastern corner of UK the occultation will be full with Jupiter disappearing from sight behind the waning crescent moon. Most of Southern UK will see the Moon grazing Jupiter, while the rest of us will see a near miss, but the pairing will still be worth looking at or trying to capture.

Three minor planets join the big boys in the skies this month. Ceres is the largest asteroid in the inner Solar System. Now designated a dwarf plant it represents a third of the mass of the asteroid belt and ; Vesta, the minor planet is the second most massive asteroid and is currently being orbited by NASA’s Dawn spacecraft. From midmonth these two will join Jupiter and Venus in the predawn sky and will travel through the Hyades in Taurus towards the Northeast. At the beginning of July Mars and Saturn can still be seen low in the constellation of Virgo in the Southwest as the Sun sets. Mercury will reach greatest eastern elongation on July 1st. This is when the planet will be furthest from the Sun, as seen from Earth, and the best time to view the innermost planet. Look for Neptune and Uranus an or so past midnight, toward the end of the month. Neptune to the South in Aquarius while Uranus is to the Southeast in Pisces. ; Throughout July Uranus is joined in the sky by Pallas, the third of our minor planets this month and possibly the largest irregular shaped object in the Solar System.

The Summer Triangle contains quite a few deep sky objects. The magnificent Ring Nebula M57 is in Lyra just below Vega. This is a beautiful planetary nebula, a shell of ionized gas from a dying red giant star. M27 is the Dumbbell Nebula in Vulpecula or little fox constellation. This is another gorgeous planetary nebula with the largest known white dwarf star at its heart. The Summer Triangle points the way down to Sagittarius, the archer. This lies between us and the very centre of the Milky Way making it one of the richest areas of the night sky. The emission nebulas, M8 the Lagoon nebula and M17 called the Omega, Swan, Lobster or Horseshoe nebula are found here along with the Trifid nebula M20 which contains an open cluster, an emission, reflection and a dark nebula.

We are now in the peak of noctilucent cloud season. For a chance to see these thin veils of blue shining clouds, look low in the Northeast before midnight or low in the Northwest after midnight. July 29th is the official peak of the Delta Aquarid meteor shower, although they can be seen from late July through to early August. They are produced by the Marsden and Kracht Sungrazing comets and have a radiant low in the Southeast and a zenithal hourly rate (ZHR) of between 15 and 20.

Starguide: June

By Jenny Winder

What to look out for in the June night sky

All eyes will be on the transit of Venus at the start of the month, but  there is plenty more for stargazers to look forward to in June.

The Moon will be full on June 4th and there will be a partial lunar eclipse visible across most of Australia, the Pacific Ocean, North and South America. It begins at 08:48 UTC and ends at 13:18 UTC. Greatest eclipse will be at 11:03 UTC when 37% of the Moon around crater Tycho will be dark and take on a red colour due to refraction of sunlight through Earth’s atmosphere.  New Moon will be on June 19th and Summer Solstice occurs for the Northern hemisphere at 23:09 UTC on June 20th. From then on the nights will get longer.

The big show happens between June 5th and 6th when Venus makes the last transit across the face of the Sun this century. Transits happen in pairs, after 121.5 years  a pair of transits occur 8 years apart, then 105.5 years pass before another pair of transits with an 8 year gap between and the pattern repeats. So the next transit after this wont be until 2117. There have only been 6 transits since the invention of the telescope and only 4 since the invention of photography. Transits have been used in the past to calculate the distance to the Sun and the size of our Solar System. This transit will be visible across most of the globe, apart from much of West Africa, the Atlantic & South America. The UK will only see the tail end of the transit after Sunrise at around 04:47 BST. Times for the transit are: First contact at 22:03 UTC  June 5th. Greatest transit at 01:29 UTC  June 6th and last contact at 04:54 UTC June 6th. You will need to find a good location with a clear view of the Eastern horizon. Remember you must never look directly at the Sun, be sure to use proper solar filters or eclipse glasses to view this once in a lifetime event.

Three related constellations grace the night sky to the South this month. Lying beneath the keystone of Hercules, Ophiuchus, (the Serpent Bearer) bisects the Serpens constellation in two holding the serpent by its head (Serpens Caput) and its tail (Serpens Cauda) With prolonged astronomical twilight at this time year we are firmly in globular cluster season and Ophiuchus boasts no fewer than 33 of them. M10 and M12 were both discovered in 1764 by Charles Messier. M10 is about 83 light years across and 14,3000 light years away while M12 is 73 light years in diameter and 15,700 light years from Earth. M5 in Serpens Caput is 655 light years across, making it one of the largest globular clusters known. It is also one of the oldest associated with our galaxy at 13 billion years old. M16 in Serpens Cauda is the amazing Eagle Nebula an active star forming region that contains the open star cluster NGC 6611 and also the ‘Pillars of Creation’ made famous by the 1995 image taken by the Hubble Telescope.

Starguide: May

By Jenny Winder

What to look out for in the May night sky

Starwatchers have plenty to occupy themselves with this month.  The  Full Moon on May 6th  will coincide with the peak of the Eta Aquarid meteor shower in the East, cutting down the zenithal hourly rate (ZHR) considerably from its usual 40 meteors per hour. New Moon will be on May 2oth and on May 26th the waxing crescent Moon will occult M67, an open cluster of stars in the constellation of Cancer.

Venus is nearing the Sun in preparation for the transit across its surface in early June, so the planet dips below the horizon shortly after sunset. If you are quick you will see Venus’ crescent phase grow in diameter as the month progresses, from 37 arcseconds at the start of May to 56 arcseconds at the close of the month. Now is also a good time to look for the elusive Ashen Light, a subtle glow on the unlit part of Venus, similar to earthshine seen on the Moon, but much fainter. This phenomenon was first described in 1643 but has never been verified. Many have claimed to see it, but many more have not. Nobody has been able to image it and nobody knows what causes it. Saturn is still a spectacular sight low toward the South in Virgo, with the rings well displayed and  casting shadows on the surface of the planet, while the shadow cast by the planet onto the rings will grow more prominent with time.

Virgo still fills the Southern sky so take the opportunity to look at the Virgo Cluster of galaxies. There are as many as  2000 galaxies in this cluster which comprises the heart of the Virgo Supercluster, part of the Local Group of galaxies that includes our own Milky Way. The Cluster is made up of a mix of spirals and elliptical galaxies

The globular cluster M13 in Hercules lies high in the South, between the Summer sky’s two brightest stars: Arcturus in Boötes to the right & Vega in Lyra to the left. Hercules is easily recognised by its ‘Keystone’ asterism and M13 lies along side nearest to Arcturus.

To the right of Arcturus lies the small constellation of Coma Berenices, containing eight Messier objects including M53, another globular cluster of stars and the Black Eye Galaxy M64 with its distinctive dark band of dust that gives this spiral galaxy its name.

We are now entering the season of nocilucent clouds. Most of the time astronomers curse the sight of clouds for obscuring the stars but these clouds are eagerly awaited. At this time of year, between May and August the Sun remains close to the horizon and illuminates the layer of water ice that lies between 76 km and 85 km in the part of Earth’s atmosphere called the Mesosphere. The clouds appear as a fine veil of glowing blue filaments. Look low in the Northwest from 21:00 and 23:00 UT or between 01:00 and 03:00 UT low in the Northeastern sky.

By Jenny Winder

Astronomy-Amateur Author: Halfblue via Wikimedia-Commons

What to look out for in the April night sky

The constellation Leo dominates the Southern sky this month. Look for the ‘Sickle’ asterism  like a back to front question mark with the bright star Regulus at the base. On April 3rd look for Mars near Regulus above the almost full Moon. On April 15th Mars reaches its stationary point, halting in its westward journey across the sky, before moving back eastward from April 16th.

Venus and Jupiter are going their separate ways after giving us a spectacular conjunction last month and we will lose Jupiter from the night skies by the end of the month. Venus is still brilliant enough at magnitude -4.4 to be seen in daylight, setting in the northwest after midnight. On April 2nd to 4th it will pass through the Pleiades in Taurus. By April13th it will form a triangle with the Pleiades & Hyades & they will be joined by the waxing crescent Moon on April 23rd.

Saturn, near Spica in Virgo to the left of Leo, reaches opposition to the Sun, as seen from Earth, on April 15th. This means it will be visible all night. It is also closest to Earth in its orbit so bigger & brighter. The rings are currently at a favourable tilt to Earth and appear brighter during opposition due to the Seeliger effect: usually the particles that make up Saturn’s rings cast shadows on the particles behind, making them darker, but during opposition the shadowed particles are hidden behind the fully illuminated particles with the net effect that the rings appear at their brightest.

Also in Virgo,  below the main pattern of stars, lies the Sombrero Galaxy, M104. This unbarred spiral galaxy is a magnitude 9.5 and  28 million Light Years from Earth. It contains one of the most massive, supermassive black holes ever measured in a nearby galaxy.

The Moon this month will be Full on April 6th and New on April 21st. Luckily this New Moon coincides with the peak of the Lyrid meteor shower, giving the best conditions (clear skies permitting) to view the typically bright trails of this shower. The Lyrids were first noted by the Chinese in 687BC which makes them the oldest meteor shower recorded. They are caused by the debris from Thatcher’s comet and usually have a Zenithal Hourly Rate (ZHR) of 10 to 20, this is the typical number of meteors seen per hour, under the ideal conditions of a dark sky, if the radiant were directly overhead. The lyrids have been known to produce unexpected peaks of up to 100 meteors per hour so is worth making the effort to see. The radiant lies in the constellation of Lyra which rises at about 10pm in the Northeast. Wrap up warm & either lie on the ground or in a reclining garden chair. Look about 45 degrees from the radiant or most meteors will pass either side of  your head.  As with all meteor showers the best time to view them is after midnight, the hours before dawn being best as the Earth’s rotation brings the observer to a position where the meteors are striking our atmosphere head on.