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.

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