Friday, April 13

Confirm the satellite of an asteroid?! In the early-morning hours of Saturday April 14th, telescope users from the eastern Great Lakes through New England have a chance to catch the asteroid 113 Amalthea occulting an 11th-magnitude star, clouds permitting — and possibly to confirm and characterize Amalthea's small moon, tentatively discovered by amateurs during an occultation last year. Full details, and get finder charts and other helpful materials from the top line here. Good luck!

• This is the time of year when, as the last of twilight fades away, the bowl of the dim Little Dipper extends straight to the right of Polaris. High above the end stars of the Little Dipper's bowl, you'll find the end stars of the Big Dipper's bowl.

Saturday, April 14

• After dark, Leo walks horizontally across the meridian high in the south. His brightest star is Regulus, the bottom star of Leo's Sickle. The Sickle forms his front leg, chest, mane, and part of his head.

Not far from Regulus, the red long-period variable star R Leonis this week should still be near its maximum brightness, magnitude 5.4 or so. There's also the tiny Frosty Leo Nebula nearby to hunt out, and galaxy groups to explore. Make a night of it with your scope using Bob King's Put a Little Bit of Leo in Your Life, with finder charts and photos.

Sunday, April 15

• Right after dark, Orion is still in the southwest in his spring orientation: striding down to the right, with his belt horizontal. The belt points left toward Sirius and right toward Aldebaran and, farther on, the Pleiades.

• New Moon (exact at 9:57 p.m. EDT).

Monday, April 16

• Vega, the bright "Summer Star," rises in the northeast shortly after dark these evenings, depending on your latitude. Exactly where should you watch for it? Spot the Big Dipper very high in the northeast. Look at Mizar at the bend of its handle. If you can see Mizar's tiny, close companion Alcor (binoculars make it easy), follow a line from Mizar through Alcor all the way down to the horizon. That's where Vega will be.

Moon, Venus, Aldebaran, Hyades, Pleiades, April 17-19, 2018
The waxing crescent Moon joins up with Venus, then Aldebaran, in the western twilight.

Tuesday, April 17

• Venus and a super-thin crescent Moon form a lovely pair low in the west as twilight fades, as shown here. They're about 5° apart at the time of twilight for the longitudes of the Americas.

• Saturn is at aphelion and the in fact farthest it's been from the Sun (by a trace) since 1959.

Wednesday, April 18

• Now the crescent Moon hangs close to Aldebaran at dusk, cradled in the Hyades for skywatcher in North America (as shown here). The Moon occults Aldebaran for parts of northern Canada.

Arcturus is the narrow point of the Kite of Boötes, climbing the eastern sky after dark these evenings. Below the head of the kite is the semicircle of Corona Borealis.

Thursday, April 19

• Arcturus shines brightly in the east these evenings. The Big Dipper, high in the northeast, points its curving handle lower-right down around toward it. Arcturus forms the pointy end of a long, narrow kite asterism formed by the brightest stars of Boötes, the Cowherd. The kite is currently lying on its side to Arcturus's left, as shown here. The kite is 23° long, about two fist-widths at arm's length.

Moon crossing Gemini, April 19-21, 2018
The Moon crosses Gemini as it approached first quarter. (The Moon is drawn three times its actual apparent size.)

Friday, April 20

• This evening the dark limb of the crescent Moon will occult 4th-magnitude multiple star Nu Geminorum for parts of the southern U.S. and points south. For rough time estimates at your location, interpolate between the time predictions in the April Sky & Telescope, page 48.

Saturday, April 21

• Now the Moon, almost first quarter quarter, shines lower left of Pollux and Castor after dark.

• The Lyrid meteor shower should be weakly active from about midnight tonight until the first light of dawn Sunday morning. The Moon, nearly first quarter, sets around 2 a.m. local daylight-saving time. The shower may produce about a dozen meteors visible per hour for a watcher under an excellent dark sky.


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 guide to astronomy.

Pocket Sky Atlas, jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Larger view. Sample chart.

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, is the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide 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."

This Week's Planet Roundup

Jupiter with Great Red Spot on April 1, 2018
Jupiter's Great Red Spot was almost exactly on the planet's central meridian when Christopher Go took this image at 20:01 April 1st UT, in below-average seeing, using a 14-inch scope on his home balcony in the Philippines. It was just one Jupiter rotation after the Juno orbiter imaged the area around the Great Red Spot close up. "The wake of the GRS is just chaos!" Go writes. "The South Tropical Disturbance is violently interacting with the GRS."
Saturn with new white spot on April 1, 2018
A new storm has appeared in Saturn's North Polar Region. It's the elongated white spot near the bottom in this image, which Damian Peach took at 8:55 April 1st UT with the 1-meter Chilescope. The spot was discovered three days earlier. To have any chance of detecting it visually, you'll likely need at least a 10- or 12-inch scope with excellent optics during really excellent seeing. "Interestingly," says Peach, "it's only the second storm on Saturn I've seen in the last two decades that I could actually see during the live video capture, the other being of course the great 2011 storm."

Mercury remains hidden in the glow of sunrise.

Venus (magnitude –3.9) shines brightly in the west in twilight. It sets a little after night becomes complete. In a telescope (look early!) it's a tiny disk 11 arcseconds wide and slightly gibbous: the Sun lights 92% of its width. As night comes on, the Pleiades glitter delicately above it. They move down closer to it every evening.

Mars and Saturn, in Sagittarius, are up after 1 a.m. daylight-saving time. By the beginning of dawn they're two bright points in the south-southeast, above the fainter Sagittarius Teapot. Mars, slightly brighter, is on the left. Their separation widens from 6° on the morning of April 14th to 10° on the 21st.

Mars is brightening on its way to an unusually close opposition in late July. It's 10 arcseconds wide now and magnitude 0.0, compared to Saturn's +0.5. Their color difference is obvious.

Jupiter (magnitude –2.5, in Libra) rises shortly after dark and shines as the brightest point in the late-night sky. It's now just three weeks from its May 8th opposition, so it appears about as bright and big (44 arcseconds wide) as it will get this year. It's highest in the south, presenting the sharpest views in a telescope, around 2 a.m. daylight-saving time.

Uranus is hidden in conjunction with the Sun.

Neptune is deep in the skyglow of dawn.


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 that also depend on longitude (mainly Moon positions) are for North America.

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


"Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious."
— Stephen Hawking, 1942–2018


"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


"Objective reality exists. Facts are often determinable. Vaccines save lives. Carbon dioxide warms the globe. Bacteria evolve to thwart antibiotics, because evolution. Science and reason are not a liberal conspiracy. They are how we determine facts. Civilization's survival depends on our ability, and willingness, to do so."
— Alan MacRobert, your Sky at a Glance editor


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



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