Planets Mars and Uranus meet in the evening sky

The late winter juxtaposition of inner and outer planets continues with a close conjunction of Mars and Uranus in the evening twilight of Wednesday, March 11th. Timing your observation will be important, as you want the sky dark enough to see the pair — but leave it too late and they will be too close to the western horizon to see clearly. AN graphic by Ade Ashford

Occurring exactly a week after its close pairing with Venus, Uranus’ conjunction with Mars is somewhat wider and the contrast in brightness not so great, but the pair’s proximity to the horizon in deep twilight means that you’ll need to pick your time carefully to see them so that the sky will be dark enough to see Uranus, but not so late that the pair will be too close to the horizon. An hour after sunset is about the ideal time, something you can determine with our Almanac.

This is a simulated telescopic view of Mars and Uranus at 50x magnification around 7 pm on 11th March. Under average skies, Uranus may be a challenge to glimpse just ¼° away from Mars — much depends on the quality of your optics, too. This orientation of Uranus with respect to Venus assumes a Newtonian telescope with an inverted view on an alt-azimuth mount; with an equatorial mount, Uranus will lie above Mars in such a telescope. In a refractor, Schmidt-Cassegrain or Maksutov telescope with a star diagonal, Uranus will lie below Mars. AN graphic by Ade Ashford

As with last week’s event, let Venus be your guide. Mars and Uranus will lie 8° (about the apparent length of your thumb with your arm outstretched) to the lower right of the brightest planet.

The separation of Mars and Uranus will be just ¼°, half the apparent size of the Full Moon. In your telescope, choose an eyepiece that gives you about 50x magnification (tip: our Scope Calc can help with eyepiece selection) so that you have a field of view close to one degree, if possible.

The close proximity of Mars makes finding Uranus easy since they will be in the same low-power telescopic field of view, but their difference in brightness will be 4.6 magnitudes, or 70 times.

Mars is currently on the far side of the Sun as seen from Earth, so it displays a gibbous phase. At magnitude +1.3, the Red Planet is 98% illuminated and displays a tiny 4.1-arcsecond disc since it’s 2.28 astronomical units (212 million miles; 341 million kilometres) away.

Contrast this with gas giant Uranus, the third largest planet in the Solar System, that lies a staggering 20.90 astronomical units (1,943 million miles; 3,127 million kilometres) from Earth tonight — nine times further away than Mars. Uranus will appear as a tiny 3.4-arcsecond disc shining at magnitude +5.9.

If you get the chance to see Mars and Uranus together through a telescope, consider the contrast not only in the brightness of these worlds as seen from Earth, but their physical characteristics: Mars is a rocky, terrestrial planet with a rarefied atmosphere half the size of Earth, while Uranus is four times larger than our planet and gaseous in composition. Clear skies!