The month of May is named for Maia, the Roman goddess of fertility, whose name means “the great one.” As the Earth once again transforms its surface into a fresh green hue as the northern hemisphere reawakens, the sky above is also always changing and showing us new things every night if we know what to look for. We are also halfway through spring now, and the days and nights are warming up, making it more inviting to spend some time outside to enjoy and learn more about our farther surroundings beyond the limits of our planet.

There are three major highlights this month, and then three more minor highlights that are good to know about, but will be harder to see for yourself.

One of the most exciting and rare events for the whole year of 2016 will happen for 7.5 hours on Monday, May 9. Starting at 7:12 a.m. EDT, Mercury will pass directly across the face of the sun from the lower left to the lower right part of our sun, following a similar path that Venus took in its own transit on June 8, 2004. Then Venus had another spectacular transit on June 5, 2012. Now we will have to wait until December of 2117 for the next Venus transit.

The last transit of Mercury took place just under 10 years ago, on Nov. 8, 2006. That happened to be the 350th anniversary of Edmund Halley’s birthday in 1656. Mercury transits, occurring about 13 times per century, are much less rare than Venus transits, which happen eight years apart, and then have a long gap of over 105 years.

Right now Mercury transits can only happen in May and November and Venus transits can only happen in June and December, but those months do slowly shift. The next time both planets will transit across the face of the sun at the same time will be July 26 of the year 69,163. The Venus transit on April 5 of 15,232 will happen during a total eclipse of the sun. The fact that we know all this so precisely shows you how mathematical the solar system really is and how much it can tell us about past and future events and their significance.

Our first planet will finish crossing over the sun at 2:39 p.m. The beginning and the end of this transit will be the best times to watch. It will take three full minutes for the diameter of Mercury to completely enter the sun and three more minutes for it to completely exit the sun. You will need a telescope with a good solar filter to watch this event. Mercury is almost 200 times smaller than the sun, so it will appear smaller than many of the sunspots on the sun. However, it will appear as a very dark and round circle, unlike sunspots, which are not as round and have a lighter grayish area around them called the penumbra.

You will get a good sense of the inner workings of our solar system by watching and photographing at least some of this event and really thinking about what is happening, especially if you also saw one or both of the recent Venus transits, which formed a much larger black spot and even displayed a glimpse of its very hot, 900-degree atmosphere as it exited the sun back on June 8, 2004. It showed an ephemeral, semicircular silvery arc sharply etched against the deep blackness of space as it was emerging from the sun for a few minutes. That gave me and the others watching that foggy morning a visceral and visual sense of the incredibly hot atmosphere of Venus, making it jump out of the textbooks in living and unexpectedly vivid contrast as it was moving and unfolding right in front of our eyes a mere 26 million miles out, or just over two minutes away at the speed of light.

Mars will be the star of the night sky all this month and into June. The red planet starts the month rising around 10 pm, but it will reach opposition on the 22nd, when it will rise exactly at sunset and remain in the sky all night long. Mars will become almost as bright as Jupiter, even though it will appear only about half as large as Jupiter in the sky. As the Earth catches up with Mars in our respective orbits around the sun, Mars will be only 47 million miles away, and Jupiter is about 10 times farther away and getting fainter and smaller after its March 8 opposition. This is the best opposition of Mars in 11 years, even though it does reach opposition every 26 months.

Try to look at the red planet with a telescope this month and next and you will see some of its dark markings, its polar icecaps, some of its atmosphere, and maybe even one or both of its moons, Phobos and Deimos. By late May, Mars will be just above its famous rival star, Antares in Scorpius. The Greek word for Mars is Ares, so Antares means “rival of Mars”. Notice that Mars will be about six times brighter than Antares, which is actually an incredible orange supergiant star that is about 700 times larger than our own sun. Then Saturn will also join the pair by 11 p.m. in the southeastern sky later this month.

One more highlight easily visible for everyone this month will be the Eta Aquarid Meteor shower. That will peak on the morning of Thursday, May 5 into Friday, May 6. You can expect about 20 meteors per hour as you will be seeing tiny, sand grain-sized pieces of Halley’s Comet smashing into our thin atmosphere about 70 miles straight up at about 40 miles per second, leaving glowing, incandescent trails behind them for a second or less. The entire comet will not return until 2061, but you can see pieces of it twice every year in the form of the Eta Aquarids in May and the Orionids every Oct. 21.

The three events not visible without a telescope are another Comet named Pan-STARRS tracing a nice arc through Aquarius, where the all the Aquarids will emanate from, and a fainter comet named 9P Tempel 1 crossing right over the orbit of the asteroid named 6 Hebe, which could be the source of up to 40 percent of all the meteors that hit our atmosphere. These two related objects, this fairly large asteroid and much smaller comet, will cross over in Leo the Lion, near its tail, which is marked by a star named Denebola, which means “tail” in Arabic.

Comet 9P Temple 1 might ring a bell, since that was the comet that we purposely hit with an 815- pound copper smart impactor back on July 4, 2005. The collision created a lot of heat and light and a crater about 100 yards across blowing a large plume of this comet’s material into space, which we then analyzed with the Deep Impact spacecraft.

May 5: The Eta Aquarid meteor shower peaks under moon-free skies. On this day in 1961 Alan Shepard became the first American in space aboard the Freedom 7 capsule.

May 6: New moon is at 3:30 a.m. EDT and it is at perigee or closest to the earth today.

May 8: The moon passes one degree north of Aldebaran in Taurus this morning.

May 9: Mercury transits the sun today for 7.5 hours. It is also at inferior conjunction. Jupiter is stationary today, ending its fourmonth long retrograde loop whose midpoint on March 8 marked its last opposition.

May 12: On this day in 1931, the Adler Planetarium in Chicago became the first planetarium in the western hemisphere.

May 13: First quarter moon is at 1:02 p.m.

May 14: On this day in 1973, our first space station, named Skylab, was launched.

May 15: The moon passes just two degrees south of Jupiter this morning.

May 18: The moon is at apogee, or farthest from Earth today at 252,235 miles.

May 21: The moon passes 7 degrees north of Mars this evening. Full moon is at 5:14 p.m. This is also called the Planting, Milk, or Flower Moon. Mercury is stationary, ending its retrograde.

May 22: Mars is at opposition this morning. The moon passes three degrees north of Saturn this evening.

May 29: Last quarter moon is at 8:12 a.m.

May 30: Mars comes closest to Earth today at 46.8 million miles.

— Bernie Reim is an amateur astronomer and teaches astronomy lab courses at the University of Southern Maine.

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