Starwatch: The July night sky

The Sun is creeping southwards again, but it may be late July before we notice that our nights are perceptibly longer and darker. While we do have chances to spy all the planets, Mercury and Venus are far from easy and Saturn is trekking lower into our W evening twilight.

By our star map times, the appropriately named Summer Triangle formed by Deneb, Altair and Vega dominates the S sky. Look for the Plough in the NW, the Square of Pegasus in the E, and remain on the alert for noctilucent clouds above the NW to NE horizon, perhaps near Capella in Auriga.

For the next two weeks, Mercury sinks from about 9° high in the WNW at sunset to set itself 75 minutes later. Dimming from mag -0.7 to 0.1 during the fortnight, it is a difficult binocular object in the fading twilight and might best be caught on the 4th when it lies 24° to the right of the young Moon.

Saturn stands 14° to the right of Spica in Virgo in the lower SW sky at nightfall and is setting in the W by our map times. At mag 0.9 and just brighter than Spica, it still lies close to the double star Porrima and is above the Moon on the 7th.

Jupiter rises below Aries in the ENE some 30 minutes after our map times and outshines every star at mag -2.2 to -2.4 as it climbs to stand well up in the E to SE before dawn. Look for it near the Moon on the 24th. Mars, mag 1.4 and reddish in hue, is 8° below-left of the Pleiades as it rises into the twilit NE sky at 02:45 BST on the 1st. By the 27th, though, it rises at 02:00 and should be obvious in a darker sky 8° below-left of the waning Moon between the horns of Taurus.

Venus, brilliant at mag -3.9 but soon to be lost in the Sun‘s glare, rises in the ENE about 55 minutes before the Sun on the 1st and stands 6° high at sunrise.

The most trivial of partial solar eclipses occurs over the far Southern Ocean to the S of South Africa on the 1st.

July diary

1st 10h New moon and partial solar eclipse

3rd 03h Moon 5° S of Mercury

4th 16h Earth farthest from Sun (152,102,197km)

8th 05h Moon 8° S of Saturn

8th 07h First quarter

15th 08h Full moon

20th 06h Mercury furthest E of Sun (27°)

23rd 06h Last quarter

24th 02h Moon 5° N of Jupiter

27th 18h Moon 0.5° S of Mars

30th 20h New moon

* Times are BST.

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