"There's A Little Black Spot On The Sun Today..."

Well, not today. Hi, this is Ben Rubel, Macomber's resident astronomer, and a member at the Macomber Center. I'm writing this to inform you of a once-in-a-lifetime opportunity! Er, I mean 14 times in a lifetime (give or take). This rare event, on Monday, May 9th, happens when the solar system’s innermost planet, Mercury, transits (passes directly between Earth and) the sun!

First, here are a few facts about Mercury: 

Mercury in false color. False color is when different wavelengths outside of the human range or different mineralogical makeups are represented by colors we can see. Credit: NASA. 

Mercury in false color. False color is when different wavelengths outside of the human range or different mineralogical makeups are represented by colors we can see. Credit: NASA. 

·       Mercury is around a third larger in diameter than our moon, but about five times more massive. 

·       Although Mercury is the closest planet to the sun, with an average distance of approximately 36 million miles, it is not the hottest planet. That honor goes to Venus, which is about twice as far from the sun as Mercury is. 

·       Mercury is relatively "cool." Its temperatures fluctuate wildly because its very thin atmosphere can't retain any heat: daytime temperatures top out at around 801° Fahrenheit, while nights bottom out at around -280°F.

·       Mercury's year (the time it takes to orbit the sun) is only 88 Earth days. A planet’s distance from the sun correlates directly with its orbital period, so, the closest planet, Mercury, has the shortest year in our solar system. 

A composite of many exposures of Mercury's 2006 transit. Credit: NASA/ESA.

A composite of many exposures of Mercury's 2006 transit. Credit: NASA/ESA.

So, now, down to business: Since only Mercury and Venus are closer to the sun than Earth is, only these planets can transit the sun. Mercury transits the sun 13-14 times per century—about once every 7 years. Venus transited the sun most recently in 2008 and 2012, but, sadly, the next Venusian transit won’t be until 2117. Of course, observers from any other planet in our solar system would be able to see Earth transit the sun. For example, astronauts on Mars will be able to witness a transit of Earth in 2084.

Now, the question on everyone's mind: How can I witness the May 9th transit of Mercury? Well, you will need a telescope with a solar filter. Never look at the sun without a solar filter! "But," you may be saying, "I don't have a telescope with a solar filter!" Well, on May 9th, from around 9:30am until the transit ends at 2:42pm, I will have my telescope, with its solar filter, set up at the Center, and anyone who wants to can come and have a look. Of course, if it’s overcast we won’t be able to see it, but light to moderate cloud cover should be fine. I hope to see you there! 


Ben Rubel, the author, also has a weekly astronomy video series called Rubel's Rambles. It can be found on the Macomber Center's Facebook page.