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Now is a great time for observers of Mars as the famous "Red planet" reaches opposition on May 22nd in Scorpius. On this day it peaks at mag. -2.1 and for a short time rivals the normally more brilliant Jupiter in brightness. However although visible all night long, due to its southern declination Mars is much better placed from Southern Hemisphere and tropical latitudes rather than northern temperate locations. For example on May 22nd from London, England the planet rises at 20:55 and sets at 05:02, a visibility period of about 8 hours. Whereas from Sydney, Australia it rises at 16:52 and sets at 07:00 hence visible for over 14 hours. In addition, Mars reaches a maximum altitude of just 17 degrees above the southern horizon from London. For comparison from Sydney it peaks at 77 degrees above the horizon, effectively appearing overhead.

Hubble Space Telescope image of Mars on August 26, 2003 (credit:- NASA/J. Bell/M. Wolff)

The orbit of Mars is eccentric which means the difference in distance between its closest (perihelion) and furthest (aphelion) points to the Sun are considerable. At perihelion Mars is 1.3815 AU (206.7 million kilometres or 128.4 million miles) distant whereas at aphelion it increases to 1.666 AU (249.2 million kilometres or 154.9 million miles). This corresponds to an orbital eccentricity of 9.3% compared to just 1.7% for the Earth. Hence the brightness and apparent size of Mars as seen from Earth vary greatly depending on the position of the two planets in their respective orbits.

What makes a Mars opposition special is that they don't occur as often as other planets. Generally speaking, Jupiter, Saturn, Uranus and Neptune reach opposition once every year but Mars takes roughly 780 days from one to the next. The reason is due to orbital dynamics; Mars is closer to us hence moves faster compared to the other outer planets and therefore it takes the Earth twice as long to catch up.

Mars and Saturn during May 2016 (credit:- freestarcharts)

Mars and Saturn during May 2016 - pdf format (credit:- freestarcharts)

This year's opposition is the best since 2005. The planet's apparent size peaks at 18.6 arc seconds and a telescope under good seeing conditions will reveal surface markings. When viewed through a 100mm (4-inch) instrument it's possible to spot the polar cap as well as major features such as the Syrtis Major. On initial observation the planet may appear bland but with time and patience it's possible to tease out subtle details. Don't be afraid to push up magnification. Also, larger telescopes fair better with more finer details visible. Another consequence of the eccentric Martian orbit is that closest approach to Earth occurs eight days after opposition on May 30th. The two planets are then separated by 0.5032 AU (75.279 million kilometres or 46.776 million miles).

The surrounding region of sky also contains first magnitude red supergiant star Antares (α Sco - mag. +1.0) and Saturn (mag. 0.0). Of the three objects Mars is easily the brightest followed by Saturn and then Antares. On May 21st, the full Moon passes 6 degrees north of Mars.

The co-ordinates of Mars at opposition are: R.A. = 15hr 57m 28s and Declination = -21d 36m 55s (J2000)

Moon, Mars and Saturn as seen around midnight on May 22, 2016 from London, England (credit:- stellarium/freestarcharts)

See also

The Planets this Month - May 2016