Graphic: Finbarr Sheehy

The Summer Triangle formed by Deneb in Cygnus, Vega in Lyra and Altair in Aquila occupies its rightful place high in Britain's S sky at our map times this month. Arcturus in Bootes is conspicuous as it sinks in the W and Capella in Auriga twinkles low down in the N. Sagittarius straddles our S horizon, its main stars forming the Teapot asterism which can only be appreciated if we travel southwards so that it climbs free of the horizon haze.

Jupiter is all but lost in our NW evening twilight at present, but Mars stands some 20° high in the SW and sets in the WSW by our map times. Currently to the right of the star Spica in Virgo, it dims from mag 0.0 to 0.4 in July as it tracks 15° to the ESE, passing N of Spica for the third time this year on the 13th. Now under 10 arcsec in diameter, it shrinks further as it recedes and is past its best for telescopic study.

The Moon lies below Regulus in Leo on the evening of the 1st, close to Mars on the 5th and to Saturn on the 7th. The latter, mag 0.4 to 0.5, is 18 arcsec wide with its rings tipped at 21°, and is almost stationary 2.5° NE of the double star Zubenelgenubi in Libra. They can be found in the SSW at nightfall and sinking in the SW by our map times.

The brilliant morning star Venus (mag -3.9) rises in the NE at 03:00 on the 1st and 20 minutes later by the 31st, climbing almost 15° high by sunrise. As it moves eastwards between the horns of Taurus it serves as a guide to Mercury which stands less than 8° below-left of Venus from the 10th to the 23rd as it brightens from mag 0.8 to -0.8.

Britain is too far N to see the best of the Delta Aquarids meteor shower which lasts from about 12 July to 23 August and peaks on the 29th. Its medium speed meteors diverge from a point that climbs from the SE horizon at our map times to pass 20° high in the S before dawn.

Ice crystals near 82km high are visible as noctilucent clouds or NLCs low down between the NW after dusk and NE before dawn. Catching the sun's light after normal clouds are in darkness, they appear like ripples or striations of silvery or electric-blue cirrus. We enjoyed a decent display on the night of 19-20 June, and more can be expected before the NLC season ends in mid-August.

July diary

2nd 11h Venus 4° N of Aldebaran

5th 13h First quarter

6th 02h Moon 0.2° S of Mars

8th 03h Moon 0.4° S of Saturn

12th 12h Full moon

12th 19h Mercury furthest W of Sun (21°)

13th 00h Mars 1.4° N of Spica

19th 03h Last quarter

21st 16h Saturn stationary

24th 19h Moon 4° S of Venus

24th 22h Jupiter in conjunction with Sun

27th 00h New moon

29th Peak of Delta Aquarids meteor shower

* Times are BST