Mars and the Transit of Mercury


Hubble Space Telescope image of Mars at opposition in 2003.

Credit: NASA, J. Bell (Cornell U.) and M. Wolff (SSI)

This month Mercury and Mars are lining up at opposite sides of the sky. The first of these planetary juxtapositions climaxes Monday, the 9th, when Mercury is in same direction as the Sun, then Sunday, May 22, Mars is on the other side of Earth, directly opposite the Sun.

Seen from Earth, Mercury appears to cross the Sun’s disk on May 9. The event is first of its kind since 2006, and is best experienced online or on television, unless you’re knowledgeable about how to use a telescope safely for solar observing. NASA plans live coverage of the Mercury transit the morning of May 9.

During the transit, begining 7:12 a.m. Eastern Time and concluding 2:42 p.m., Mercury appears as a tiny black dot, gradually progressing across the solar disk. Remember, although Mercury appears to be traversing the Sun, it’s not physically close. Monday morning May 9 Mercury is about 42 million miles from the Sun, nearly as far as it ever gets—43.3 million miles. At perihelion, the closest Mercury approaches the Sun, their separation is about 29 million miles.

Sunday, May 22, Mars is directly opposite the Sun, as Earth lines up exactly between both objects that day. Mars is currently retrograding in apparent sky motion relative to background stars, as Earth catches up with the slower orbiting planet. Our closest proximity is reached May 30. By then, Mars is vivid, appearing about as bright as Jupiter for the first time in a decade. With its rusty color, views of the “red” planet shouldn’t be missed.

If you’ve never spotted Mars, May 21, the night before opposition, provides a good opportunity to get personally acquainted. The Full Moon is then just six degrees of arc north of the red planet. Due to the Moon’s brilliance, blocking its light with your hand helps make Mars easier to see that night.

Tuesday evening, May 30, at 7 p.m., Joe Rao and I will be at the Hayden Planetarium doing our Astronomy Live presentation about Mars. Perhaps we’ll see you then.