May is named for the Greek goddess Maia, the first-born, most beautiful and shyest of the seven Pleiades sisters, daughters of Atlas and Pleione. May is the  fifth month of the Gregorian calendar, which most countries have used since Pope Gregory XIII decreed it in 1582, after talking with Christopher Clavius and Johannes Kepler, two German math and astronomy professors. They had to better compute the date of Easter (the first Sunday a fortnight after the first Full Moon after vernal equinox), as the Julian calendar, in use since 45 BC, was a bit longer than the Earth’s orbital period around the Sun, and that caused problems with the Easter computation. Even now, we must occasionally make small corrections to match our calendars to the Earth’s orbit (e.g., Leap Year, which adds a day to February).
THE PLANETS
In the morning this month, Venus shines brilliantly low in the east, out over the ocean. It’s the second planet from the Sun (Earth is third), so when Venus is at inferior conjunction, between Earth and Sun, it’s fairly close to Earth – only about 26 million miles away. Venus’s cloud-tops are unusually reflective, making Venus the third brightest natural object we can see, after only the Sun and Moon. Venus is about the same size as Earth, so astronomers call her “Earth’s sister planet,” but she’s more like our evil twin.
At 860° year-round, Venus is the hottest planet in our solar system — even hotter than Mercury - because of the runaway greenhouse effect. Unlike Mars which is covered in sand-dunes, Venus’s surface is all rock: the sulfuric acid rain never reaches the ground before being vaporized by the heat. The atmospheric pressure is over 90 times Earth’s, like being 2,000 feet down under the ocean, enough to crush one of our modern submarines. Although the surface winds are a constant five knots, the density of the atmosphere would prevent you from walking against them (assuming a space-suit could be devised to withstand the heat and pressure).
Venus is unique in some nice ways: Its orbit is the roundest in our solar system; it is the only planet with a female name (its symbol is the same one doctors use for Earthly women); its temperature (though Hellish) is quite uniform all around the planet, as the atmosphere circulates evenly until it enters a double vortex at the south pole; and it rotates clockwise (all the other planets and sun rotate counter-clockwise). But, its tilt is the least of all the planets. How nice. I’ll still take Louisiana in July, though it’s a close call (don’t tell Pam).
Mercury is dipping down in the east and can be seen only the first few days this month. Mars is to the lower left of Venus in the morning. Jupiter is up earlier each morning and coming into viewing range. Saturn sits below the constellation Leo and is always worth finding in a telescope — I used my nephew’s little Tasco-brand scope in Georgia last week and we could see the rings just fine, even though they are edge on to us these days. Toward the end of May, Neptune is the blue dot next to Jupiter, which is easy to find next to the Last-quarter moon on the 17th.
THE STARS
After sunset , the white winter star Procyon is low in the west, and yellow Capella is in the northwest. Almost straight overhead is the constellation Leo, the Lion — the reverse question mark shape serves as his head, and his body reclines to the left of it. That’s golden Saturn gliding below him, and a bit further east is the red-giant star Arcturus, the alpha-star in Boötes, the Herdsman. You can find Arcturus using the Big Dipper’s handle to “arc” toward it. It’s the second brightest star in the northern hemisphere, and no wonder, it gives off 180 times more light than the Sun and is only 44 light-years away. To the northeast is Vega, the fast-spinning alpha star in Lyra, and low in the southeast is Antares, the super-giant “heart of Scorpio” and the biggest star we can see, 700 times the diameter of the Sun.
THE CALENDAR
May 1- First-quarter Moon is high at sunset; Saturn is to its upper left. Sunrise is at 5:34 a.m. and sunset is at 7:42 p.m. If you can see the Pleiades star cluster in the west, you may notice an interloper, Mercury passing in front.
May 2- Venus is at its biggest and brightest this morning.
May 8- Full “Flower” Moon rises at 7:52 p.m. out over the islands. It might be a nice night for a moonlight walk along the backshore.
May 14- The Moon’s at apogee today, the furthest away it gets in its elliptical orbit.
May 17- Last-quarter Moon is high at sunrise; Jupiter is to its lower right. With a telescope, from 4 a.m. to 5 a.m. you can watch the shadows of two of Jupiter’s moons, Io and Callisto, pass across its cloud-tops.
May 18- Neap tide this month is just 6.4 feet between high and low, but that will double in a couple of weeks.
May 20- Waning crescent Moon is above Venus in the pre-dawn sky, but you’ll have to be up early to see it. Tomorrow morning it’s off to the left of Venus. This morning, Neptune appears so close Jupiter you could easily mistake it for one of Jupiter’s moons (it’s really 2.4 billion miles behind it).
May 24- New Moon means dark skies for hunting galaxies, star-clusters and nebulae, but the Moon is also on the same side of Earth as the Sun, and they’re combining their gravitational attraction and pulling our ocean tides higher.
May 26- The Moon’s at perigee, closest to Earth this month, bringing us spring tides over the next two days with a difference of 12.7 feet between the highest tides in the middle of the night and the lowest tides first thing in the morning (well, 7 a.m. today).
May 31- Sunrise is at 5:03 a.m. and sunset is at 8:14 p.m., giving us over 15 hours of sunlight. Summer solstice is only 3 weeks away.