Moon, Mars, Saturn at dawn April 6, 7, 8, 2018
The waning Moon shines with Mars and Saturn in early dawn. (The Moon is positioned for an observer near the middle of North America; it's exact for latitude 40° N, longitude 90° W. The Moon is drawn three times its actual apparent size. The visibility of fainter objects in morning twilight is exaggerated.)

Friday, April 6

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

• As dawn approaches on Saturday the 7th, you'll find the waning Moon bunching up with Mars and Saturn, as shown here.

Saturday, April 7

• At this time of year, the two Dog Stars stand vertically aligned around the end of twilight. Look southwest. Brilliant Sirius in Canis Major is below; Procyon in Canis Minor is high above.

• Last-quarter Moon tonight (exactly so at 3:18 a.m. April 8th EDT). The Moon rises around 2 or 3 a.m. your local daylight saving time, some 8° or 10° to the lower left of Mars and Saturn. By dawn on the 8th they're all well up in the south-southeast, as shown here.

Sunday, April 8

• Jupiter's moon Europa disappears into eclipse by Jupiter's shadow around 2:52 a.m. Monday morning EDT (11:52 p.m. Sunday evening PDT). A 2-inch telescope will show it gradually fading away just west of the planet.

Monday, April 9

• Vega, the bright "Summer Star," rises in the northeast around 9 or 10 p.m. these evenings. 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 make its appearance.

Tuesday, April 10

• Capella is the bright star high in the west-northwest during and after dusk. Its pale-yellow color matches that of the Sun, meaning they're both about the same temperature. But otherwise Capella is very different. It consists of two yellow giant stars orbiting each other rather closely every 104 days.

Moreover, for telescope users, Capella is distantly accompanied by a tight pair of red dwarfs: Capella H and L, magnitudes 10 and 13. Article and finder charts.

Wednesday, April 11

• High above the Big Dipper late these evenings, nearly crossing the zenith for mid-northern skywatchers, are three pairs of dim naked-eye stars, all 3rd or 4th magnitude, marking the Great Bear's feet. They're also known as the Three Leaps of the Gazelle, from early Arab lore. They form a long line roughly midway between the Bowl of the Big Dipper and the Sickle of Leo.

According to the Arabian story, the gazelle was drinking at a pond — the big, dim Coma Berenices star cluster — and dashed away when startled by a flick of Leo's nearby tail, Denebola. Leo, however, seems quite unaware, facing the other direction.

Thursday, April 12

• Right after dark, find Procyon high above brilliant Sirius in the southwest. Look upper left of Procyon by 15° (about a fist and a half at arm's length) for the dim head of Hydra, the enormous Sea Serpent. His head is a group of 3rd- and 4th- magnitude stars about the size of your thumb at arm's length.

About a fist and a half lower left of Hydra's head shines Alphard, his 2nd-magnitude, orange heart. The rest of Hydra zigzags (faintly) from Alphard all the way down to the southeast horizon.

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 — and possibly 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.


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 is hidden in the glow of sunrise.

Venus (magnitude –3.9) shines brightly low in the west in twilight. It sets just after night becomes complete.

Mars and Saturn, together in Sagittarius, rise around 2 a.m. daylight-saving time. By the beginning of dawn they're two bright points in the south-southeast, just above the fainter Sagittarius Teapot. They're pulling apart now: from 3° apart on the morning of April 7th (when the Moon shines with them) to 6° on the 14th.

Mars is brightening on its way to an unusually close opposition in late July. It's still only 9 arcseconds across, but it's now brighter than Saturn; they're about magnitude +0.1 and +0.5, respectively. Their color difference is obvious.

Jupiter (magnitude –2.4, in Libra) rises around 10 p.m. daylight-saving time to shine as the brightest point in the late-night sky. It's now just a month before opposition and 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 or 3 a.m. daylight-saving time.

Uranus and Neptune are lost behind the glare of the Sun.


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



Image of Anthony Barreiro

Anthony Barreiro

April 6, 2018 at 4:01 pm

In Greek mythology, the nine-headed water snake Hydra is female.

The southern constellation Hydrus, the male water snake, was included in Lacaille's 1756 planisphere of the southern sky.

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