This Week's Sky at a Glance, May 30 – June 8

FRIDAY, MAY 30

■ The Big Dipper hangs down by its handle in the northwest these evenings. The middle star of its bent handle is Mizar, with tiny little Alcor right next to it.

On which side of Mizar should you look for Alcor? As always, on the side pointing toward Vega! Which is the brightest star shining way off in the east, 53° away.

■ Titan casts its shadow on Saturn tonight. Only every 15 years does Titan, Saturn's largest moon, cross Saturn's face from Earth's viewpoint — and, more visibly, cast its tiny black shadow onto Saturn' globe. A new series of these events has begun. They will continue every 16 days until October.

Tonight Titan's shadow crosses Saturn's face from 9:05 UT to 14:53 UT May 31st; that's from 5:05 a.m. to 10:53 a.m. Eastern Daylight Time May 31st; 2:05 a.m. to 7:53 a.m. PDT May 31st. Since Saturn is only up in view for a short while before and during early dawn at any given location, these times mean that only western North America is favored. And it's fairly likely that blurry seeing when Saturn is so low will make the shadow undetectable even in a largish telescope. So hope for steady air! As the months proceed, the situation will improve. See Bob King's Titan Shadow Transit Season Underway.

SATURDAY, MAY 31

■ The crescent Moon is approaching Mars this evening. They're about 4° apart at nightfall in North America, as shown below.

But that's just their apparent separation: the way they appear projected on the surface of the celestial sphere. In actual 3-D space the Moon is only 1.3 light-seconds distant from us, while Mars is currently 650 times farther in the background at a distance of 14 light-minutes.

SUNDAY, JUNE 1

■ Now the Moon leaves Mars behind to get chummy with Regulus, shining only about 1° from it this evening (depending on your location). But at a distance of 79 light-years, Regulus is 1.9 billion times farther from us than the Moon is. A scale model: If the Moon were just a foot from your eye like a bug on your windshield, Regulus would be 360,000 miles in the background — about at the Moon's actual distance from us!

MONDAY, JUNE 2

■ First-quarter Moon (exact at 11:41 p.m. EDT). After dark the Moon shines between the dim hind feet of Leo: 4th-magnitude Sigma and Rho Leonis. Above the Moon by 15° look for 2nd-magnitude Denebola: Beta Leonis, the lion's tail tip.

TUESDAY, JUNE 3

■ To most of us, "Cassiopeia" means "Cold!" Late fall and winter are when this landmark constellation stands high overhead (for mid-northern latitudes). But even on warm June evenings, it still lurks low. As twilight fades out, look for it down near the north horizon: a wide, upright W. The farther north you are the higher it'll appear, but even as far south as San Diego and Atlanta, all of its stars will be above the horizon.

WEDNESDAY, JUNE 4

■ Have you ever seen Alpha Centauri?! At declination –61° our brilliant, magnitude-zero neighbor is permanently out of sight if you're north of latitude 29°. But if you're at the latitude of San Antonio, Orlando, or points south, Alpha Cen skims just above your true southern horizon for a little while late these evenings.

When to look? When Alpha Librae, the lower-right of Libra's two brightest stars, is due south over your landscape. That's about 10 p.m. now (depending on where you live east-west in your time zone). At that time, drop your gaze 45° straight down from Alpha Lib.

THURSDAY, JUNE 5

■ The waxing gibbous Moon hangs high in the south as the sky darkens after sunset. How soon can you spot 1st-magnitude Spica emerging into view 5° or 6° to its left? When watching for a star or planet to come into view in a bright twilight sky, you'll look and look and it won't be there, then suddenly it pops out and stays more or less steadily in view. You wonder why you missed it.

The reason you missed it because the center of your vision had to land precisely on it, by chance, as you patiently searched. That's because your vision is sharp only at the very center of your retina (the fovea centralis). Away from there your vision gets quite blurry, meaning low-resolution, the more so the farther into your peripheral vision. At low resolution, a tiny bright point blurs away completely if it mixes with a bright background.

And why, exactly, did that take you by surprise?

Because our brain's visual system does not show us what the eye shows the brain. If it did, wherever you looked you'd see a little patch of sharp detail straight ahead surrounded by more poorly-resolved patches of shape and color growing larger and larger the farther they are into your peripheral vision. This would look like staring down a round tunnel with patterns on its sides: the patterns would look tiny in the distance, and larger and larger the closer they are to you, out to the edges of your vision.

The reason you don't experience your view being projected on tunnel walls like that (except under psychedelics or near-death brain disturbances) is because our perceptual system evolved to construct a useful, 3-D mental model of our surroundings in their actual space. Your neural model of the world in which you move, an abstract encoding that exists in the few cubic inches your skull, evolved to enable us and other animals to operate successfully in the actual external world. The illusion that we perceive the outside world directly is an unconscious shortcut to save processing power. Else you'd always have to decipher jumbles of tunnel illusions deliberately.

This is another reminder that our conscious experience of reality is a limited information-processing phenomenon — it's not external reality itself. The two are radically different orders of being. The history of science has been the slow unfolding of this revelation.

And that is why Spica is first not there, then surprisingly suddenly it is.

FRIDAY, JUNE 6

■ After dark, Vega is the brightest star high in the east. Barely lower left of it is 4th-magnitude Epsilon Lyrae, the Double-Double. Epsilon forms one corner of a roughly equilateral triangle with Vega and Zeta Lyrae, as shown below. The triangle is less than 2° on a side, hardly the width of your thumb at arm's length.

Binoculars easily resolve Epsilon. And a 4-inch telescope at 120× or more should resolve each of Epsilon's two components into a tight pair.

Zeta Lyrae is also a double star for binoculars, but much tougher. It's unresolved in the photo below but is plainly an unequal pair in nearly any telescope.

Delta Lyrae, below Zeta, is a much wider and easier pair, gold and blue.

SATURDAY, JUNE 7

■ The Big Dipper hangs high in the northwest at nightfall. The Dipper's Pointers, currently its bottom two stars, point lower right toward Polaris. Above Polaris, and looking very similar to it, is Kochab, the lip of the faint Little Dipper's bowl. Kochab passes exactly over Polaris around 9:30 or 10 p.m., depending on how far east or west you live in your time zone. Check by comparing them to a vertical line, such as the edge of a building.

SUNDAY, JUNE 8

■ The nearly full Moon (it'll be full on Tuesday night the 10th) shines well to the upper right of Antares this evening, as shown below. This is the view in twilight. As night advances, the scene moves higher and tips leftward toward the south.

This Week's Planet Roundup

Mercury is very deep in the glare of sunset. Good luck with binoculars. Don't confuse it with brighter, easier Jupiter also down there.

Venus, brilliant at magnitude –4.4, rises almost due east just before the beginning of dawn (about two hours before sunrise). Once Venus is up in the clear you can't miss it. . . until the sky grows too bright. How long can you follow Venus farther up until it's lost in the growing light of day? Or will you discover that, with time and very sharp vision, you can still see Venus through the blue sky of day? See June 5th above.

In a telescope, Venus's globe is about half lit.

Saturn, much dimmer, is higher in the dawn, moving ever farther to Venus's upper right. See the Saturn entry below.

Mars (magnitude +1.3, in Cancer) remains in the west in the evening. It's the orange dot less than a fist to the right of Regulus, the brightest star of Leo and the bottom of the Leo's Sickle. Mars and Regulus are still very nearly equal in brightness.

Watch them close in on each other. Their separation shrinks from 10° on May 30th to 6° on June 6th. They'll have a close conjunction on June 16th and 17th, passing 0.8° apart.

In a telescope, sadly, Mars is now just a fuzzy blob 5½ arcseconds in diameter.

Jupiter (magnitude –1.9) is disappearing into the sunset. You might try for it with binoculars just above the west-northwest horizon 30 or 40 minutes after sunset. If you spot a tinier point nearby late in the week, that's Mercury. Good luck; see the June Sky & Telescope, page 46.

Saturn is the other dawn planet in addition to Venus. But at magnitude +1.1 it's only about 1/200 as bright. Look early. Binoculars will help locate Saturn 23° upper right of Venus on the morning of May 30th: about two fists at arm's length. They widen to 30° apart by June 7th.

If you get your telescope on Saturn in the low-altitude poor seeing, expect a fuzzy little cheeseball with a surprisingly low surface brightness, very slightly oval, with signs of a toothpick stuck though it diagonally. The toothpick is Saturn's rings; we see them nearly edge-on this year.

Uranus is hidden in conjunction with the Sun.

Neptune, a telescopic "star" at magnitude 7.9, lurks in the background of Saturn about 1° to its left (celestial northeast) just before dawn begins. All this year, use the finder chart for Neptune with respect to Saturn that's in the June Sky & Telescope, page 51. Using a pencil, put a dot on the path of each planet for your date.

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. UT is also known as UTC, GMT, or Z time.

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 a more detailed 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.

For the attitude every amateur astronomer needs, read Jennifer Willis's Modest Expectations Give Rise to Delight.

Once you get a telescope, to put it to good use you'll need a much more detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas, in either the original or Jumbo Edition. Both show all 30,000 stars to magnitude 7.6, and 1,500 deep-sky targets — star clusters, nebulae, and galaxies — to search out among them.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many, as well as many more deep-sky objects. It's currently out of print, but maybe you can find one used.

The next up, once you know your way around well, are the even larger Interstellarum atlas (with 201,000+ stars to magnitude 9.5 and 14,000 deep-sky objects selected to be detectable by eye in large amateur telescopes), and Uranometria 2000.0 (332,000 stars to mag 9.75, and 10,300 deep-sky objects). And 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. The pinnacle for total astro-geeks is the new Annals of the Deep Sky series, currently at 11 volumes as it works its way forward through the constellations alphabetically. So far it's up to H.

Can computerized telescopes replace charts? Not for beginners I don't think, and not for scopes on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting technology to work rather than learning how to explore the sky. 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 and a curious mind." Without these, "the sky never becomes a friendly place."

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn't simple either. Do learn the essential tricks at How to Use a Star Chart with a Telescope.

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

"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; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence."
            — John Adams, 1770