Sky Notes July 2015

Sky Notes for July 2015          Geoff Mitchell

The summer solstice (June 21st) has now passed; the Earth reaches Aphelion (furthest point of its orbit around the Sun on July 6th at a distance of 152 million km (95 million miles) and the evening twilight noticeably fades earlier throughout the month. The July night sky shows the summer constellations prominently in the south east from late evening and the late spring constellations disappear into the western twilight. The bright planet Jupiter is now low in the evening twilight and both Jupiter and Venus set less than two hours after the Sun by month end. Venus shines brightly, telescopes shows Venus has phases (rather like our Moon).  Currently Venus is approaching the earthward part of its orbit around the Sun, increasing in apparent size from 35 to 48 arc second as phase changes from 30% down to a thin crescent just 10% phase in late July.  Venus now moves steadily towards our daytime sky during late July and reaches inferior conjunction in mid August.  A 13% lit thin crescent moon joins Venus and Jupiter in the western twilight on July 19th when a local public open observing evening is planned as part of the Bradgers Hill s weekend events (refer to the home page for more information)

The summer night sky contains many fine objects to view for the enthusiast in the late evening hours but also has a few notable events of special interest.  Look to the NW  from half an hour to two hours after sunset  or similarly  to the NE  hours before sunrise  i.e. when the Sun just below the horizon during the summer months when extremely high clouds at 80 km altitude known as Noctilucent Cloud (NLC) may be seen. NLC’s show a bluish colour and also show filamentary structure.

Our own Milky Way galaxy stretches from the constellation of Auriga [The Charioteer], marked by the bright star Capella and through the constellations of Perseus and Cassiopeia all now positioned low in the north.

In the south east the summer constellation of Cygnus [The Swan] now seen as evening twilight fades. The Milky Way can be seen as a faint band of stars stretching low in the east down through constellations of Aquila [The Eagle], Scutum [The Shield] and towards Sagittarius [The Archer] and Scorpius [The Scorpion] in late evening skies, use binoculars to see the myriad of stars in these rich star clouds, best seen on clear dark moonless evenings from darker locations outside the town.  Sagittarius is best seen in June / July, the constellation is known for the `Teapot` asterism of stars has rich star fields and some fine star clusters  located above the spout of the Teapot  asterism; however you do need a good southern horizon and finder chart to spot some of these.  Pluto is located just above `the handle of the teapot asterism` and it is a thought to note that NASA’s New Horizon space probe is due to flyby Pluto in mid July. Similarly another Dwarf planet Ceres, a binocular object magnitude 7.8 located in the obscure constellation of Microscopium [The Microscope] and reaches opposition on July 25th and currently has the NASA DAWN space probe orbiting it and has revealed some rather intriguing white areas on a darker surface.

Hercules is noted for the Globular cluster M13 containing some 750,000 stars, a nice view in a small telescope The bright star Vega in the constellation of Lyra [The Lyre] is seen low above the north east horizon and Altair in the constellation of Aquila low in the east. Vega, Altair and Deneb, in the constellation of Cygnus form the `Summer Triangle` asterism, a useful sign post for the summer skies.

Look low in the SE late evening to find a yellowish star and the distinctive `T` shaped asterism of stars of the `head` of Scorpius , the yellow star is in fact the ringed planet Saturn which reached opposition on May 23rd.  Although rather low as seen from the UK, its ring system is now wide open, a classic view of this gem of the solar system. Small telescopes will show the rings and the brightest moon Titan. Larger telescopes show up to six or so fainter moons and any white oval features on the planets disk.  Look below the `T` head of Scorpius to see the `blood red` coloured star Antares.  Antares name means `The rival of Mars`, a red super giant star, with a mass of some 20 solar masses. It has a diameter that, on the scale of our solar system, would be greater than the orbit of Mars. High in the south the bright orange star Arcturus in the constellation of Bootes [The Herdsman] is the brightest star in the northern hemisphere of the sky.

July also has two Full Moon dates (July 2nd and 31st), the later being referred to as a `blue moon` i.e. the second full moon in the same calendar month but not a change to the Moon’s colour.

 

Planets in July

Mercury returns low in the evening twilight from mid month but is poorly placed

Venus shines brightly and is positioned low in the west after sunset visible in evening twilight.

Mars is now positioned in the dawn skies following  conjunction in mid June.

Jupiter and Venus head into the evening twilight and are best seen mid month in July

Saturn now rises by early evening in Libra / Scorpius – a good time to see this ringed `gem`.

Uranus is placed in our pre dawn skies – best views in autumn skies.

Neptune is placed in our pre dawn skies – best views in autumn skies.

Moons phases in July

New Moon         July 16th                Moonless, best time for deep sky observing.

First Quarter     July 24th                Best days to see shadow details in lunar craters (early evening)

Full Moon            July 2nd/31st         Best days to see bright ray craters like Copernicus / Tycho.

Last Quarter      July 8th                 Moon visible in daytime skies.  Do not look directly at the Sun.

Meteor showers        Southern δ Aquarids, maxima around 30th July, poor in bright moonlight.

Capricornids, several maxima in July, bright yellow / blue meteors, low rates.

The highlights of the month

Venus dominates the evening twilight, showing a thin crescent as the phase changes (30% to 10%) during July

Jupiter and Venus close together in the evening twilight until late July

Saturn low in south east, rings open at 24° DE [tilt] showing Saturn’s North Pole.

3 day old Moon, in evening twilight after sunset on July 19th very low in NW with Regulus, Jupiter and Venus

Noctilucent cloud – watch the NW skies from 30 minutes to 2 hours after sunset (see text)

More detailed sky notes and LAS Newsletters, Finder charts are available to LAS members via the Members` page on the LAS Website www.lutonastrolink.org.uk  Artificial satellite and International Space Station visible passes and bright Iridium flares – check the  home page for posting s of details of favourable observing times.

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