Comet 41P / T-G-K in bowl of Big Dipper, March 24, 2017
Comet T-G-K (green blob) crossing the bowl of the Big Dipper on March 24th. Photography greatly overemphasized the comet's low-surface-brightness coma compared to the overexposed 2nd- and 3rd-magnitude Dipper stars. Chris Schur used a 50-mm f/3.5 lens for 105 minutes of exposure.

TWO binocular comets are now in view!

The first is Comet 41P/Tuttle-Giacobini-Kresak, or "T-G-K", behaving as expected. It's visible in amateur telescopes and large binoculars high in the northern evening sky. It's about magnitude 7, depending on your instrument (larger apertures result in fainter estimates), and it's likely to be about 6th magnitude all April. It appears fairly large, since it's passing relatively close to Earth; mostly diffuse and low-surface-brightness but with a sharp nucleus. Use low power and a wide field early in the week before the evening Moon gets very bright. See article. (Use the finder chart in that article; the charts in the May Sky & Telescope are significantly off.)

Comet C/2017 E4 Lovejoy is the surprise. Discovered on March 10th at magnitude 12, it was only expected to reach 9th magnitude at its brightest in mid-April. But it has already leapt up to 7th, similar to T-G-K — and it's more condensed so it's easier to see. It's in Pegasus, in the east just before the beginning of dawn; go out 2 hours before your local sunrise time (if you're in the world's mid-northern latitudes). The Moon won't interfere until about the morning of the 7th. See article and finder charts: Comet Lovejoy Brightens Quickly, Heads North.

Moon, Mercury, Mars and the Pleiades, March 29-31, 2017
The waxing crescent Moon hangs with Aldebaran, the Hyades and Pleiades in the last evening in March. (These scenes are drawn exact for the middle of North America.)
Mars and Mercury at dusk, early April 2017
By the end of the week Mercury has greatly faded. . .
Moon and Regulus, April 6, 2017
. . .while the waxing Moon has moved on to shine on the other side of the sky.

Friday, March 31

• The waxing crescent Moon is approaching Aldebaran and the Hyades this evening, as seen at right.

• The huge, bright Winter Hexagon is still in view after dusk, filling the sky to the southwest and west. It's the biggest well-known asterism in the sky. Start with brilliant Sirius in the southwest, the Hexagon's lower left corner. High above Sirius is Procyon. From there look even higher for Pollux and Castor, rightward from Castor to Menkalinan and bright Capella, lower left from there to Aldebaran (near the Moon tonight), lower left to Rigel at the bottom of Orion, and back to Sirius.

Saturday, April 1

• Mercury this evening is at its highest sunset altitude of the year for skywatchers around 40° north latitude. Look for it moderately low in the west about 45 to 60 minutes after sunset. Fainter Mars is 15° above it.

• This evening Aldebaran is lower right of the Moon, and Betelgeuse is a bit farther to the Moon's lower left (for North America). Have you ever closely compared the colors of Betelgeuse and Aldebaran? Can you detect any difference in their color whatsoever? I can't, really. Yet Aldebaran, because it's spectral type K5 III, is often called an "orange" giant, while Betelgeuse, spectral type M1-M2 Ia, is usually called a "red" supergiant. Their temperatures are indeed a bit different: 3,910 and 3,590 kelvins, respectively.

A complication: Betelgeuse is brighter. And to the human eye, the colors of bright objects appear, falsely, to be desaturated: appearing paler (whiter) than they really are.

Sunday, April 2

• The Moon shines in the top of Orion's dim, upraised Club this evening, under the feet of Gemini.

Monday, April 3

• First-quarter Moon (exact at 2:29 p.m. EDT). The Moon after dark shines under Pollux of the Castor-and-Pollux pair. The Moon is a similar distance upper right of brighter Procyon. Look way below Procyon for Sirius, brighter still.

Tuesday, April 4

• Now the Moon forms a huge, nearly vertical line with Procyon and Sirius below it in early and mid-evening.

Wednesday, April 5

• Near the end of twilight at this time of year, Arcturus, the bright "Spring Star" climbing in the east (well to the left of brighter Jupiter), shines at the same height as Sirius, the brighter "Winter Star" descending in the southwest (for skywatchers at mid-northern latitudes).

Thursday, April 6

• The waxing gibbous Moon pairs with Regulus, the leading light of Leo. How soon in twilight can you first spot Regulus? Watch them cross the sky together through the night. They set just before the beginning of Friday's dawn.

Friday, April 7

• Jupiter is at opposition, in the opposite direction from the Sun as seen from Earth. It climbs into grand view in the southeast through the evening, with slightly bluer Spica below it.

This is, however, Jupiter's most distant opposition since 2005; it's magnitude –2.5 and in a telescope appears 44.2 arcseconds across its equator. Jupiter reaches almost 50″ wide at the maxima of its opposition cycle. This last occurred in 2010 and will again in 2022.

Saturday, April 8

• Vega, the bright "Summer Star," rises in the northeast not long after dark now. Exactly where should you watch for it to come up? Spot the Big Dipper almost overhead 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 makes its appearance.


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 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the new Jumbo Edition for easier reading in the night. Click image for larger view.

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 Red Spot on March 24, 2017
Jupiter on March 24th. "Condition was perfect today," writes imager Christopher Go. Details in the Great Red Spot are well resolved. Note the unusually wide turbulent wake to its following (celestial east) side. South is up.

Mercury (about magnitude 0 and fading) sparkles in evening twilight low in the west. It's still about at its highest for 2017, even as it dims.

Venus (magnitude –4.2) is very low above the east horizon as dawn brightens. Having just passed through inferior conjunction (on March 25th) it's still a thin crescent in a telescope, but now it's thickening daily instead of thinning.

Mars (magnitude +1.5, in Aries) is the orange "star" moderately low due west in late twilight, about 15° upper left of Mercury. Don't confuse it with Aldebaran far to Mars's upper left.

Jupiter (magnitude –2.5, in Virgo) comes to opposition on April 7th. It rises around sunset, shines low in the east-southeast after nightfall, high in the southeast by 11 p.m., and highest due south around 1 a.m. daylight saving time. Spica hangs 7° below it. In a telescope Jupiter is 44 arcseconds across its equator.

Saturn over Sagittarius at dawn, early April 2017
On any clear morning this week, look south in early dawn to say an early hello to Saturn over the Sagittarius Teapot — a scene that will become a signature of 2017's summer evenings. (The blue 10° scale is about the width of your fist at arm's length.)

Saturn (magnitude +0.4, in Sagittarius upper right of the Teapot) rises in the early morning hours and glows in the south by early dawn. Redder Antares (magnitude +1.0) twinkles 19° to Saturn's right. Saturn doesn't reach opposition until June 14th.

Uranus and Neptune are hidden in the glow of dusk and dawn, respectively.


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 (UT, UTC, or GMT) minus 4 hours.


"This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours."
— Neil deGrasse Tyson, 2014

"Objective reality exists. Facts are often determinable. Vaccines stop diseases. Carbon dioxide warms the globe. Science and reason are no political conspiracy; they are how we determine reality. 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

Stand against falsehoods, denialism, and suppression of research. March For Science on April 22nd, in Washington DC and 410-plus other cities and towns, to “champion publicly funded and publicly communicated science as a pillar of human freedom and prosperity.”