This Week's Sky at a Glance, May 6 – 14

FRIDAY, MAY 6

■ To the right of the thick crescent Moon this evening shine the two heads of the Gemini twins, as shown below. In springtime the stick-figure twins stand upright, settling downward.

SATURDAY, MAY 7

■ Lower right of the Moon by almost 20°, look for Pollux and Castor lined up roughly horizontally. They form the top of the huge Arch of Spring. Lower left of them, bright Procyon marks the Arch's left end. Farther to the lower right from Pollux and Castor are 2nd-magnitude Menkalinan (Beta Aurigae) and then brilliant Capella, the Arch's right end.

■ What is the oldest thing you have ever seen? For everybody in the world it's at least the Sun and other objects of the solar system, age 4.6 billion years. Nearly everything on the Earth's surface is much younger, even the oldest mountains and landforms. And to be technical about it, the material of the Sun's surface changes almost from minute to minute as convection cells of hot gas rise, spread, and sink.

But the bright regions of the face of the Moon, visible to the naked eye, average some 3.9 billion years old, while most of the Moon's gray maria date from 3 to 3.5 billion years ago.

Some meteorites in museums and collections come from about 4.5 billion years back.

For most people, the next object from deeper in time is Arcturus, the brightest star very high toward the southeast these evenings. Most people have surely seen it whether they knew it or not, since it's one of the brightest stars in the sky. It's a Population II orange giant, age about 7 billion years.

Amateur astronomers have globular clusters. Most of these are older still, at least in part. White dwarfs in the familiar glow of M4 in Scorpius have been dated at 12.7 ±0.7 billion years. So that probably applies to the rest of M4 too, or most of it.

But individual super-old stars that you can observe? For that you want Bob King's article In Search of Ancient Suns with its finder charts. Assigning dates to individual stars from the first eras after the Big Bang is still iffy; astronomers have to work from the near-absence of heavy elements in their spectra. But a 6th-magnitude star in Bootes and a 7th-magnitude star in Libra, both in binocular range, await you these May and June nights. They probably date from about 12½ billion and at least 13 billion years ago, respectively. These and a few others in the article will probably be the oldest things you have ever seen, or will.

The Big Bang itself is firmly dated at 13.8 billion years, but good luck with that unless you have microwave eyes.

One could pick nits. Pick a proton, any proton right in front of you, and it has almost certainly remained intact since the Big Bang's first millionth of a second. What a variegated history it has seen! Too bad it can't speak.

SUNDAY, MAY 8

■ First-quarter Moon (exactly first-quarter at 8:21 p.m. EDT). Now the Moon is under the front hook-end of the Sickle of Leo. The brightest star of the Sickle is the bottom of its handle, Regulus. Spot Regulus about 10° (a fist at arm's length) left of the Moon.

MONDAY, MAY 9

■ This evening the Moon forms a flat triangle with the Sickle's two brightest stars: Regulus below the Moon and Algieba to the Moon's upper left. The triangle is nearly isosceles; the Moon is about 5° from each star.

■ Can you trace out the Great Diamond? It stands some 50° tall and extends across five constellations. It's upright in the south-southeast to south during evening this week.

Start with Arcturus, its brightest star. That's its left corner. Some three fists (30°) lower right from there is Spica, the Diamond's bottom. A similar distance upper right from Spica is Denebola, the 2nd-magnitude tailtip of Leo. Almost as far upper left of Denebola is fainter Cor Caroli, 3rd magnitude. And then back to Arcturus. Robert H. Baker may have been the first to name the Great Diamond, in his 1954 book When the Stars Come Out.

The bottom three of these stars, the brightest three, form a nearly perfect equilateral triangle. We can call this the "Spring Triangle" to parallel to those of summer and winter. The first to name it such was probably the Sky & Telescope columnist George Lovi, writing in the March 1974 issue.

TUESDAY, MAY 10

■ Now the Moon shines below Leo's hindquarters.

■ Arcturus high in the southeast forms the pointy end of the long, narrow Kite asterism: the central part of Bootes, the Cowherd. The kite currently extends left or upper left from Arcturus. The kite's head is bent slightly upward. The kite is 23° long, about two fists at arm's length.

WEDNESDAY, MAY 11

■ The waxing gibbous Moon has the dim head of Virgo as its background. Look two or three fists lower left of the Moon for Spica, and three or four fists right of the Moon for Arcturus.

THURSDAY, MAY 12

■ The Moon has moved to only about one fist from Spica, which still shines to its lower left. Arcturus is three fists to the Moon's upper left.

FRIDAY, MAY 13

■ The almost full Moon is passing about 5° left of Spica this evening. Brighter Arcturus shines is 30° to their upper left.

SATURDAY, MAY 14

■ Three zero-magnitude stars shine after dark in May: Arcturus high in the southeast, Vega lower in the northeast, and Capella in the northwest. They appear so bright because each is at least 60 times as luminous as the Sun, and because they're all relatively nearby: 37, 25, and 42 light-years from us, respectively.

■ Plan for the deep total eclipse of the Moon tomorrow night, May 15th. The lunar eclipse will be visible from most of North America except the far northwest, and from all of Central and South America. The Moon, in Libra, will be high in the sky for many of these areas. For details see the May Sky & Telescope.

Europe will catch mainly the partial stage of the eclipse, toward dawn on the 16th.

A livestream of the eclipse from various sites around Europe and North America starts at 2:15 May 16th UT (10:15 p.m. May 15th Eastern Daylight Time), courtesy Gianluca Masi and the Virtual Telescope Project.

 

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This Week's Planet Roundup

Mercury, much faded, sinks out of sight in the sunset early this week.

Venus and Jupiter, magnitudes –4.0 and –2.1 respectively, are the two bright "Morning Stars" shining low in the east as dawn brightens. Jupiter is the higher one. They're pulling farther apart by 1° per day; you'll find them separated by 6° on the morning of May 6th, widening to 13° by the 14th.

Mars, magnitude +o.8 in Aquarius, glimmers roughly 10° upper right of Jupiter.

Saturn, also magnitude +0.8, is in eastern Capricornus a good 25° or so upper right of Mars.

Uranus and Neptune are unobservable low in the glow of dawn.

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All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions and graphics that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time, EDT, is Universal Time minus 4 hours. (Universal Time is also called UT, UTC, GMT or Z time.)

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Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read How to Use a Star Chart with a Telescope. (It applies just as much to charts on your phone or tablet as to charts on paper.)

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically, meaning heavy and expensive. And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

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Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the heavens above. It's free.

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"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
            — Carl Sagan, 1996

"Facts are stubborn things."
            — John Adams, 1770

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