Mars The Opposition of Mars
22 May, 2016

Image created from http://space.jpl.nasa.gov/
For animation (0.4 Meg) click here


Mars, the red planet, holds a great fascination for humans. Associated with the God of War, this fascinating world has been the subject of endless speculation on whether life once inhabited it. Currently a bevy of spacecraft are circling its frigid and arid surface taking detailed images and searching for hidden water, while two robot explorers have been ranging over it for over 4 years.

Mars Facts:
Diameter: 6794 km
Moons: 2, Phobos and Demios (Fear and Terror)
Year: 687 days
Day: 1.026 Earth days
Mass: 0.107 Earth Mass (0.64 x1024 Kg)

This year is a good opposition of Mars. Not as fantastic as the Great Opposition of Mars in 2003, and almost as good as 2005, it is the best one until 2018. This year is a great opportunity for people to observe this fascinating world. What is an opposition? Opposition refers to when a planet is opposite the Sun in the sky. This can only happen to outer planets, as Earth must pass between the Sun and the planet. The Earth passes Mars in its orbit every 26 months, and at this time we get a good view of the Red Planet.

When Mars is also making its closest approach to the Sun, our view is very good indeed. While Mars is on average 228 million km from the sun, due to Mars's elliptical orbit this varies by 42 million kilometers. If Mars is at its furthest from the Sun at opposition, Mars is also around 99 million km from Earth, while if Mars is at its closest to the Sun during opposition, this value narrows to only 57 million km. Favorable oppositions occur only once in every 15 to 17 years. During the Great Opposition of 2003, Mars and Earth were a mere 55.8 million km apart. This degree of closeness will not be achieved again until 2287. This year, Mars and Earth will be 75.3 million km apart.

Oppositions in the early months of the year, when Mars is furthest from the Sun, are always poor. The best oppositions occur around August. This is very good for Southern observers, as Mars is high in the sky, and the winter sky is usually still and transparent, ideal conditions for watching Mars. This years opposition occurs during May. The conditions are good for Southern Observers. The cooler weather makes warm clothes a must, but atmospheric turbulence is low and skies are likely to be very clear, making Mars's markings easier to distinguish. The visible disk of Mars increases in diameter, from 5 arc seconds, to 18.6 arc seconds (an arc second is approximately 1/3600th of your fingerwidth). While this sounds astoundingly small, 18 arc seconds will give a passable disk in most amateur telescopes, even the small ones from Tasco. Mars will be 1/100 th of the diameter of the Moon, about half the diameter of Jupiter and about the same size as the diameter of Saturn (Saturn itself, not the ring system, which is larger) This year, the Opposition (May 22) is earlier than the closest approach of Mars to Earth (May 31), so the best views will actually be on the days around May 31st.

What you can expect to see

Unaided eye. The best observing will be from mid May to mid June. Mars rises around sunset, so Mars is best observed from around two hours after Sunset or 9 pm standard time for most of this period. Mars is the brightest object in the sky aside from the Sun or Moon, its distinctive red colour making it easy to identify. From the 22nd to the end of May Mars is in the east at 10 pm local time, and 11 hand-spans above the eastern horizon as seen from Melbourne (when your hand is held out flat, thumb in, with your arm outstretched, your hand covers 6 degrees of sky, see diagram at right, people in Adelaide and Sydney should add an extra handspan, Brisbane and Alice Springs an extra two and from Darwin Mars is 6 hand-spans high).

Mars is in the distinctive constellation of Scorpius the Scorpion. At opposition Mars in the very head of the Scorpion near the stars Dschubba and Acab. Mars forms a triangle with Saturn and the red star Antares. On the night of opposition, 22nd Mars, Mars, the Moon, Saturn and Antares from a diamond shape in the sky. Plotting the position of Mars every few nights (use a torch covered in red cellophane to stop your night vision being destroyed while you draw its position) will be interesting as Mars heads back towards Libra. In April Mars was stationary, and reversed direction during May. This is called retrograde motion, and occurs due to Earth overtaking Mars in its orbit. A map showing this motion is here.

mars location
Evening sky on Sunday May 22 looking east as seen from Adelaide at 22:00 ACST. Mars, Saturn and Antares form a triangle. The inset shows telescopic views of Mars and Saturn. Similar views will be seen elsewhere in Australia at the equivalent local time (eg 22:00 AEST, 22:00 AWST). (click to embiggen).

Binoculars Mars is a barely visible disk on the days around closest approach with 10 x 50 binoculars and larger (although markings will not be seen with standard binoculars).

Telescopes The best time to observe Mars is when it is highest in the sky, unfortunately this occurs well after midnight for a large proportion of best viewing times, and not long after midnight for the rest. Be prepared for some late nights if you want the best telescopic views (see the Ephemeris below, Transit times are when Mars is highest).

Mars shows clearly visible markings in a 50 mm refractor telescope, and significant detail can be seen in a 4" reflector, while 6" and 8" instruments will give better detail still. No current Earth-bound telescope can reveal the huge volcano, Mons Olympus, or the huge valley of Vale Marensus, which are seen in many of the spacecraft images. However, significant features such as Syrtis major (featured in the Masthead graphic) will be visible in even a small telescope. The Martian day is about 40 minutes longer than the Earth day, so if you observe at the same time each night, you can see the surface features rotating into and out of view. Dust storms can also occur, sometimes lasting days. Wind removal and deposition of the reddish, iron rich dust can also reveal or obscure features, so Mars's appearance can be somewhat different between each opposition. Seasonal winds alternately covering and uncovering darker features with lighter dust were once interpreted as seasonal plant growth. Studying the Martian storms and the changing surface features is a valuable amateur activity.

In the May 2001 issue of SKY & TELESCOPE (pages 115 to 123), Thomas Dobbins and William Sheehan discussed rare historical observations of bright, star-like flares from certain regions on the planet Mars. They suggested that the flares might be caused by specular reflections of sunlight off water-ice crystals in surface frosts or atmospheric clouds, specifically at times when the sub-Sun and sub-Earth points were nearly coincident and near the planet's central meridian (the imaginary line running down the center of the visible disk from pole to pole). In 2001 flashes were seen by observers in the US in Edom Promontorium, near the Martian equator.

So mid May to mid June is an excellent time to dust off that old telescope lying around in the garage, or to beg a view from a friend or neighbour with a telescope. Better yet, many astronomical clubs hold open nights, and this is an excellent opportunity to see this fascinating world in a decent telescope. Also, some of the local planetariums may be showing off Mars if they have telescopes (See the Links section for addresses).

For recording the appearance of Mars, all you need is a sheet of paper on a sturdy background, a pencil (or coloured pencils if you want to try recording the colors you see), a small torch coverd in red cellophane and a watch. Make sure you and your telescope are located in a relatively dark place, and have modest circles pre-drawn on your paper (I use a 20 cent piece or my telescope eyepiece cap). Have your telescope out for a while beforehand so that it is at ambient temperature, to prevent air currents in the telescope from ruining the image. Record the date and time, and the weather (if it is windy, how much cloud, how much moonlight, what is the dimmest star you can see, etc.). Make sure you are wearing warm clothing, then make yourself comfortable at the eyepiece, preferably with a chair that allows you to sit and view comfortably, and, well, start drawing. It may take a few tries before you get the hang of recording what you see by red light, but you will feel a warm glow of accomplishment when you can. The Ephemeris below gives the time Mars rises, its magnitude, and its altitude at midnight (5 degrees is equivalent to the distance covered by an outstretched hand), and its apparent diameter in arc seconds.


Ephemeris of Mars
 	
Date           Altitude        Mag      Diam "     Distance      Rise Time    Transit    
               at Midnight                            (AU)        (ACST)      (ACST)

22 May 2016 	+76 17' 23" 	-2.0 		18.32 		0.5108042 		17:04:44 	00:16:02 
29 May 2016 	+75 44' 18" 	-2.0 		18.58 		0.5036710 		16:27:14 	23:32:32
05 Jun 2016 	+71 06' 03" 	-1.9 		18.53 		0.5050980 		15:50:30 	22:55:11
12 Jun 2016 	+64 51' 42" 	-1.8 		18.19 		0.5144907 		15:15:22 	22:19:32
19 Jun 2016 	+58 23' 53" 	-1.7 		17.63 		0.5307861 		14:42:24 	21:15:49 
26 Jun 2016 	+52 14' 37" 	-1.5 		16.93 		0.5528123 		14:11:47 	20:48:09 
03 Jul 2016 	+46 36' 06" 	-1.4 		16.15 		0.5795204 		13:43:35 	20:48:09 
10 Jul 2016 	+41 32' 42" 	-1.2 		15.35 		0.6099268 		13:17:43 	20:23:14 
17 Jul 2016 	+37 04' 11" 	-1.1 		14.56 		0.6430697 		12:54:01 	20:00:54 
24 Jul 2016 	+33 07' 49" 	-0.9 		13.80 		0.6782097 		12:32:18 	19:40:52 


These values are for Adelaide. Rise and transit times will be similar in other cites at the same local time. Transit times are when Mars transits the meridian, and is highest point in the sky. At transit, Mars will be almost at the zenith (the highest point above the horizon)in the north (well, basically almost stright up).



Here are some links to Mars sites of interest:


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Created: Saturday, 21 May 2016, 11:22:32
Last Updated: Saturday, 21 May 2016, 11:22:32