Mars The Opposition of Mars
27 July, 2018

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. The robot explorer Opportunity has been ranging over Mars's surface for for 14 years and is now hunkered down in Mars's global dust storm. The Mars rover Curiosity is a relative newcomer, with only 6 years of exploring the red planet..

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. The best since the Great Opposition of Mars in 2003, it is the best one until 2035. 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 a decent 58 million km (0.386 AU) 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 July. The conditions are good for Southern Observers. The cold 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 24.5 arc seconds (an arc second is approximately 1/3600th of your finger-width). While this sounds astoundingly small, 24.5 arc seconds will give a significant disk in most amateur telescopes, even the small ones from Tasco. Mars will be 1/76 th of the diameter of the Moon, about 2/3 the diameter of Jupiter and about the 1/3 rd bigger than the diameter of Saturn (Saturn itself, not the ring system, which is larger) This year, the Opposition July 27) is earlier than the closest approach of Mars to Earth (July 31), so the best views will actually be on the days around July 31st.

What you can expect to see

Unaided eye. The best observing will be from mid June to mid August. Mars rises around sunset, so Mars is best observed from around two hours after Sunset or 7:30 pm standard time for most of this period. Mars is the brightest object in the sky aside from the Sun, Moon or Venus (all five bright planets are visible in the sky mid to late July), its distinctive red colour making it easy to identify. Distinctive white Venus is low in the west, Jupiter in the north-north west and golden Saturn is well above and much dimmer than Mars, so spotting Mars is quite easy. From the 1st July to early August Mars is in the east at 10 pm local time. At opposition Mars is a hand-span for the Full Moon and 10 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 undistinguished constellation of Capricornius the Goat. At opposition Mars is not near anything particularly interesting. It will head towards Sagitarius in July-August, then loop back again in September. 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 Saturday July 27 looking east as seen from Adelaide at astronomical twilight, 90 minutes after sunset (18:59 ACST). Mars is close to the Moon, and below Saturn and the "teapot" of Sagittarius. The inset shows the telescopic view of Mars. Similar views will be seen elsewhere in Australia at the equivalent local time (90 minutes after sunset). (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).

Unfortunately a large global dust storm is raging at the moment, hopefully it will clear by opposition, but currently mars is a nearly featureless ball. Should it clear, 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 (other than a faintish darker spot on the surface), 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 (like the one that is occurring at the time of writing). 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 June to Mid August 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 covered 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.

If you have a mobile phone, and a decent sized telescope, you may be able to snap images of Mars, there are now a variety of mobile phone attachments for holding phones to a telescopes eyepiece. Setting the phones camera app so that you see something other than a tiny overbright dot will require some experimentation.


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

01 Jul 2018 	+54 34' 55" 	-2.1 		20.79 		0.4502525 	19:18:24 	02:32:46 
02 Jul 2018 	+55 26' 45" 	-2.2 		20.98 		0.4462250 	19:14:00 	02:28:42 
03 Jul 2018 	+56 19' 13" 	-2.2 		21.16 		0.4423089 	19:09:31 	02:24:34 
04 Jul 2018 	+57 12' 18" 	-2.2 		21.35 		0.4385061	19:04:59 	02:20:24 
05 Jul 2018 	+58 05' 59" 	-2.3 		21.53 		0.4348185 	19:00:23 	02:16:10 
06 Jul 2018 	+59 00' 15" 	-2.3 		21.70 		0.4312481 	18:55:44 	02:11:53 
07 Jul 2018 	+59 55' 04" 	-2.3 		21.88 		0.4277970 	18:51:00 	02:07:33 
08 Jul 2018 	+60 50' 25" 	-2.4 		22.05 		0.4244672 	18:46:14 	02:03:10 
09 Jul 2018 	+61 46' 15" 	-2.4 		22.22 		0.4212610 	18:41:24 	01:58:44 
10 Jul 2018 	+62 42' 33" 	-2.4 		22.38 		0.4181803 	18:36:30 	01:54:15 
11 Jul 2018 	+63 39' 15" 	-2.4 		22.54 		0.4152274 	18:31:33 	01:49:43 
12 Jul 2018 	+64 36' 18" 	-2.5 		22.70 		0.4124043 	18:26:33 	01:45:08 
13 Jul 2018 	+65 33' 39" 	-2.5 		22.85 		0.4097130 	18:21:30 	01:40:30 
14 Jul 2018 	+66 31' 13" 	-2.5 		22.99 		0.4071553 	18:16:24 	01:35:50 
15 Jul 2018 	+67 28' 54" 	-2.5 		23.13 		0.4047328 	18:11:16 	01:31:07 
16 Jul 2018 	+68 26' 39" 	-2.6 		23.26 		0.4024469 	18:06:05 	01:26:21 
17 Jul 2018 	+69 24' 19" 	-2.6 		23.38 		0.4002988 	18:00:52 	01:21:34 
18 Jul 2018 	+70 21' 47" 	-2.6 		23.50 		0.3982894 	17:55:37 	01:16:44 
19 Jul 2018		+71 18' 56" 	-2.6 		23.61 		0.3964196 	17:50:20 	01:11:51 
20 Jul 2018 	+72 15' 34" 	-2.7 		23.71 		0.3946898 	17:45:01 	01:06:57 
21 Jul 2018 	+73 11' 31" 	-2.7 		23.81 		0.3931008 	17:39:41 	01:02:02 
22 Jul 2018 	+74 06' 32" 	-2.7 		23.90 		0.3916528 	17:34:20 	00:57:04 
23 Jul 2018 	+75 00' 21" 	-2.7 		23.98 		0.3903462 	17:28:58 	00:52:05 
24 Jul 2018 	+75 52' 38" 	-2.7 		24.05 		0.3891814 	17:23:35 	00:47:05 
25 Jul 2018 	+76 43' 01" 	-2.8 		24.11 		0.3881583 	17:18:11 	00:42:04 
26 Jul 2018 	+77 31' 00" 	-2.8 		24.17 		0.3872773 	17:12:47 	00:37:02 
27 Jul 2018 	+78 16' 01" 	-2.8 		24.21 		0.3865382 	17:07:23 	00:31:59 
28 Jul 2018 	+78 57' 25" 	-2.8 		24.25 		0.3859410 	17:01:59 	00:26:55 
29 Jul 2018 	+79 34' 25" 	-2.8 		24.28 		0.3854857 	16:56:36 	00:21:51 
30 Jul 2018 	+80 06' 10" 	-2.8 		24.30 		0.3851720 	16:51:13 	00:16:47 
31 Jul 2018 	+80 31' 46" 	-2.8 		24.31 		0.3849996 	16:45:51 	00:11:43 
01 Aug 2018 	+80 50' 21" 	-2.8 		24.31 		0.3849684 	16:40:31 	00:06:38 
02 Aug 2018 	+81 01' 12" 	-2.8 		24.31 		0.3850778 	16:35:11 	23:56:31 
03 Aug 2018 	+81 03' 55" 	-2.7 		24.29 		0.3853274 	16:29:54 	23:51:29 
04 Aug 2018 	+80 58' 26" 	-2.7 		24.27 		0.3857166 	16:24:38 	23:46:27 
05 Aug 2018 	+80 45' 04" 	-2.7 		24.23 		0.3862450 	16:19:24 	23:41:27 
06 Aug 2018 	+80 24' 27" 	-2.7 		24.19 		0.3869117 	16:14:12 	23:36:27 
07 Aug 2018 	+79 57' 27" 	-2.7 		24.14 		0.3877159 	16:09:03 	23:31:29 
08 Aug 2018 	+79 24' 59" 	-2.7 		24.08 		0.3886569 	16:03:56 	23:26:33 
09 Aug 2018 	+78 47' 58" 	-2.6 		24.02 		0.3897335 	15:58:53 	23:21:39 



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 straight up).



Here are some links to Mars sites of interest:


Return to Southern Sky Watch

Link to the Lab's 'In Space' gateway Link to the Lab's home page


This page is provided by Ian Musgrave and is © copyright 2018 Ian Musgrave, except the "Southern Sky Watch" logo, as well as any other ABC logo used on this page, is © copyright of the ABC.

This page can be used freely for any non-commercial purpose but please attribute it correctly. However, see the disclaimer.

Email: reynella@internode.on.net e-mail Ian with any suggestions

Created: Saturday, 21 May 2016, 11:22:32
Last Updated: Wednesday, 21 May 2018, 11:22:32