A rare look at Mercury crossing the face of the sun
Our sky is dominated by planets this month. But first, put down your coffee and make plans to go see Mercury transiting the Sun on Monday!
The other planets in play are bright enough to be seen even from light-polluted night skies. Mars will be closest to us on May 22, when the Sun, Earth and Mars all fall on a line – a so-called “opposition.”
Mars will only be outshone by Jupiter, the brightest object in the night sky other than the Moon. Jupiter is in the southern sky at dusk. Being about 10 times farther from us than Mars, it would be dimmer than Mars if it were not 20 times bigger and several times more reflective (due to its bright cloud cover). Still – they are close in brightness, only differing by about 10 percent from our distant view. They will appear different anyway, due to their colors. Jupiter appears white due to its clouds, while Mars is reddish from its soil and its almost cloudless skies.
Mars has a fairly elliptical orbit, and that causes it to be closer to us at some oppositions than others. This is not the closest but not bad (the next “favorable” one will be in July 2018). You might recall the one in 2003 when several other factors combined to bring Mars the closest in tens of thousands of years. Yes, not by much, but still closest.
That was the start of a viral email that was incorrect in saying that in the sky, it would appear as large as the Moon. This claim was so wrong that even NASA put up a Web page debunking it. I saw one copy of the email, retyped in a colorful, fancy script (never a good sign), and only figured out what had happened when I saw an apparently original, correct version. That one made the statement but had the clause that Mars as seen in a 100-power telescope would appear the same size as the Moon seen with the naked eye. That was true.
The bogus email reappears every August even though, because of the longer orbit of Mars, we only come into opposition about every 2.135 years. Not every year. Not every August. It is fun to see tongue-in-cheek memes on Facebook poking fun at this: “The Moon will be up in the sky tonight! It has not happened since last night! It will not happen again until tomorrow night!”
Well, have some fun yourself looking at the planets this month. Drag that ol’ scope out from the closet and put in a 100x eyepiece.
Mars will look as big as the Moon!
Daniel B. Caton is a physics and astronomy professor, and director of observatories at Appalachian State University. Email: firstname.lastname@example.org. More on this month's column: www.upintheair.info.