Sky at Night Magazine - - THE SKY GUIDE JULY -


Best time to see: 28 July, 00:20 BST, (July 27, 23:20 UT) Al­ti­tude: 11º Lo­ca­tion: Capri­cor­nus Di­rec­tion: South Fea­tures: Light and dark sur­face re­gions, po­lar caps and weather Equip­ment: 3-inch tele­scope or larger

Mars reaches op­po­si­tion on 27 July at which time the planet will be look­ing its largest and bright­est. This par­tic­u­lar op­po­si­tion oc­curs when the planet is low in the sky from the UK. Mars will get to an ap­par­ent di­am­e­ter of 24 arc­sec­onds from 23 July through to 9 Au­gust, but reaches a max­i­mum al­ti­tude of 11° as seen from the cen­tre of the UK. Although this will add an ex­tra chal­lenge, take heart from the fact that for the next op­po­si­tion on 13 Oc­to­ber 2020, Mars will reach an al­ti­tude of 42° and will be only marginally smaller and less bright.

At the start of July 2018, Mars will ap­pear to be trav­el­ling east against the stars, but by the end of the month its di­rec­tion will have changed so that it ap­pears to be mov­ing west. Through a tele­scope it’s the south­ern po­lar cap of Mars that’s cur­rently tilted to­wards us, by around 12°. The dark, V-shaped fea­ture known as Syr­tis Major is cen­trally placed at 01:00 BST (00:00 UT) on 2 July.

Mars ro­tates once on its axis ev­ery 24 hours and 40 min­utes, which can lead to a de­gree of frus­tra­tion when ob­serv­ing the planet. To ex­plain this, imag­ine a fea­ture cen­trally po­si­tioned on the planet’s disc. At the same time the next day, the fea­ture would ap­pear in the cen­tral po­si­tion 40 min­utes later. The day af­ter that it would reach the cen­tral po­si­tion 80 min­utes later than on the first night, and so on. Ob­serv­ing the planet at the same time on con­sec­u­tive days es­sen­tially gives you a re-run of what you’ve been look­ing at on pre­vi­ous days! To the naked eye, Mars ap­pears to brighten im­pres­sively through­out July, start­ing off at mag. –2.2, but in­creas­ing in bril­liance to mag. –2.8 around op­po­si­tion. This makes it brighter than Jupiter and the sec­ond bright­est main planet af­ter Venus.

Mars in op­po­si­tion will shine brightly in July but an­noy­ingly it’s also very low on the hori­zon

The V-shaped Syr­tis Major is one of the most eas­ily recog­nised fea­tures on Mars

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