Viewing Mars

In Fall 2003, Mars comes very close to the Earth, providing an opportunity for detailed observations.

Background Reading: Stars & Planets, p. 347 to 355 (Mars)


This table provides simulated images and other data for Mars as it will appear at 21:30 (9:30 pm) on each Tuesday through the end of October. Each date links to an image showing how Mars will appear on that evening. The diameter column gives the angular diameter, measured in seconds of arc, of the planet itself. The altitude column gives the angle in degrees between Mars and the horizon as seen from Honolulu; large altitudes provide the best views. The longitude column indicates what part of Mars will be facing the Earth, and the final column lists surface features which should be visible.

Date   Diameter     Altitude     Longitude   Visible Features
08/26/03 25.1 28.6   88 Mare Sirenum, Solis Lacus
09/02/03 24.9 34.6   26 Mare Erythraeum, Sinus Meridiani
09/09/03 24.2 40.5 324 Sinus Sabaeus, Syrtis Major, Hellas
09/16/03 23.2 45.3 262 Syrtis Major, Mare Tyrrhenum, Mare Cimmerium
09/23/03 22.0 49.1 199 Mare Cimmerium, Mare Sirenum
09/30/03 20.6 51.9 Mare Sirenum
10/07/03 19.2 53.7 Solis Lacus, Mare Erythraeum
10/14/03 17.9 54.7 Sinus Meridiani, Sinus Sabaeus
10/21/03 16.6 55.0 Syrtis Major, Hellas, Mare Tyrrhenum
10/28/03 15.4 54.8 Mare Cimmerium

As this table shows, there is a trade-off between altitude and diameter. Mars is closest to the Earth at the end of August, and if other things were equal, we would expect the best views then. But on that date, Mars will still be quite low in the sky at 21:30; we would need to wait until midnight to take full advantage of Mars's proximity. From late August through mid September, the altitude Mars attains at 21:30 increases dramatically, while the planet's apparent diameter decreases only slightly. Thus the best views will probably be in early to mid September, when the planet is significantly higher in the sky but only slightly more distant than in late August.

Another factor to consider is the longitude, which determines which side of Mars is turned toward the Earth. Mars rotates on its axis once every 24 hours and 37 minutes, so in one week it makes 6.82 rotations. Thus, if we observe Mars every week at the same time, we will see a somewhat different part of Mars each week; the surface features which are facing directly toward the Earth one week will appear toward the edge of the planet's disk the next week. For example, Syrtis Major, the planet's most prominent feature, will appear on the east side of Mars on 09/09/03, and on the west side on 09/16/03. By observing Mars every week for five weeks or more, we will get a chance to see every part of the Martian globe (except for Mars's north pole, which is currently tipped away from the Earth).

A final factor is the weather, both here and on Mars itself. Dust storms occasionally occur on Mars; in extreme cases, they can obscure the entire surface of the planet for weeks on end! According to some experts, dust storms are more likely during summer in Mars's southern hemisphere, which begins in September 2003. To have the best chance of seeing Mars despite the real possibility of dust storms, we will observe the planet whenever possible.

WEB RESOURCES


Joshua E. Barnes (barnes@ifa.hawaii.edu)

Last modified: September 11, 2003
http://www.ifa.hawaii.edu/~barnes/ASTR110L_F03/marsviewing.html