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Which side of Mars will I see tonight?

If you haven't done so already, be sure to circle Tuesday, 6 October 2020 on your calendar. On this day at 14:13 UT (3:13pm BST) Mars lies closest to Earth for the current apparition when the distance between the centres of the two planets narrows to 0.41491 astronomical units, or 62.1 million kilometres (38.6 million miles).

The last time that the Red Planet drew nearest our own was on 31 July 2018, when the gulf between the worlds was somewhat smaller at 0.38497 astronomical units, or 57.6 million kilometres (35.8 million miles). However, what likely springs to mind from two years ago was the obscuring global Martian dust storm and the planet's very low altitude as seen from the U.K.

Mars is 8 percent farther away this time around, yet on 6 October 2020 Mars' magnitude -2.6 ochre-coloured disc attains a maximum angular size of 22.6 arcseconds against the constellation backdrop of Pisces. Since it lies slightly north of the celestial equator, the planet transits in the south around 1am local time at an altitude of almost 42 degrees for an observer in the heart of the British Isles – that's nearly 32 degrees higher in the sky than in 2018!

At its most prominent and brightest in October 2020, Mars requires a telescope magnifying little more than 80× to enlarge its disc to the same apparent size as the full Moon to the unaided eye. Note that the Red Planet spans 20 arcseconds or larger from 8 September to 1 November.

Mars' signature ochre colour helps it stand out in early autumn, rising in the east at dusk, setting in the west at dawn and outshining the brightest stars in the entire sky. If you're in any doubt about its identity, the waning gibbous Moon passes close to Mars at dawn on 6 September and 3 October. The Moon also lies close to the planet at dusk on 29 October.

While you might logically assume that 6 October is also the date that Mars reaches opposition, this is not the case. Owing to the eccentricity of the planet's orbit and that of our own, the difference between the dates of Mars' closest approach to Earth and when it lies opposite the Sun in the sky can differ by up to 8½ days. Opposition for the Red Planet occurs at 23:20 UT on 13 October 2020 which, due to daylight savings time, is 12:20am BST on Wednesday, 14 October in the British Isles.

For the latest news, information and imagery from the current apparition, be sure to read Richard McKim's 2020 Mars Opposition Blog.

Which side of Mars is facing Earth tonight?

The Red Planet can reveal a wealth of surface detail in quality telescopes of 6-inch (15-cm) aperture and larger when seeing conditions permit and the instrument is fully acclimatised to the outdoor temperature. Even a 3-inch (7.6-cm) ‘scope is sufficient to reveal larger features such as the Syrtis Major or Hellas. At the 2020 opposition, Mars' southern pole is tipped about 20 degrees towards Earth in a position angle of about 145 degrees.

However, there is always the possibility that a Martian dust storm will obscure areas of interest. With the experience of 2018 in mind, observers should be monitoring Hellas, plus the Serpentis and Solis Lacus regions for dust clouds.

Our Mars Mapper 2020-2021 web app previewed here not only helps you identify the main Martian surface features visible from mid-July 2020 through to March next year, but also generates a wealth of useful data for observers. Note that the app does not show the varying size of Mars' south polar cap, nor the planet's considerable phase several weeks before or after opposition. Mars Mapper is also available in Desktop and Smartphone flavours (the links open in new windows).

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