As the sun turns southwards, our nights begin to lengthen and the moonless spell later in July brings many of us our first dark skies of the summer. The chart shows the Plough in the NW as the Summer Triangle reaches the high meridian. Formed by the bright stars Vega, Altair and Deneb, in the constellations Lyra, Aquila and Cygnus respectively, it is bisected by the Milky Way, which arches high across our E sky from Sagittarius and Scorpius (SCO) low in the S to Cepheus, Cassiopeia and Perseus in the NE.
Many of the stars in an area of sky between Deneb and Vega were scanned by Nasa’s Kepler space telescope in its primary search for extrasolar planets. Its catalogue of discoveries, published last week, lists 4,034 possible planets, including 50 Earth-sized ones which orbit within their habitable zones.
The one bright planet visible at our July map times is Saturn, still edging westwards following its opposition in S Ophiuchus. Although it dims slightly from mag 0.1 to 0.3, it remains the brightest object low in our S sky until it sets in the SW three hours after our map times.
The moon is above-right of Saturn on the 6th when telescopes show the Saturnian disc to be 18 arcsec wide, while the rings span 41 arcsec and are tipped wide open at 26.7° in our favour. Even binoculars are enough to show that Saturn is more than just a circular dot.
Jupiter, conspicuous at mag -2.0 and now moving eastwards to the right of Spica in Virgo, stands in our lower SW sky at nightfall, where it is near the Moon on the 1st. The Moon is near again on the 28th, but by then Jupiter is lower still in the WSW as it sinks to set in the W just prior to our map times.
Venus improves as a brilliant morning star of mag -4.1 to -4.0. Rising in the NE at about 02:20 BST all month long, it reaches 19° high in the E at sunrise on the 1st, and 6° higher by the 31st. It lies 8° below-right of the Pleiades in Taurus on the 1st and slides between the Pleiades and Aldebaran to pass 3° above-left of the star on the 14th. Telescopically, its diameter shrinks from 18 to 15 arcsec and its sunlit phase grows from 63% to 74%.
July diary
1st 02h First quarter; 08h Moon 2.7° N of Jupiter
3rd 21h Earth farthest from Sun (152,092,504km)
7th 04h Moon 3° N of Saturn
9th 05h Full moon
14th 12h Venus 3° N of Aldebaran
16th 20h Last quarter
20th 01h Moon 0.4° N of Aldebaran; 12h Moon 2.7° S of Venus
23rd 11h New moon
27th 02h Mars in conjunction with Sun
28th 21h Moon 3° N of Jupiter
30th 06h Mercury furthest E of Sun (27°); 16h First quarter
* Times are BST
