Sky Guide 2017 - astronomy.com€¦ · Richard Talcott is a senior editor of Astronomy. A supplement to Astronomy magazine Sky Guide By Martin Ratcliffe 2017 and Richard Talcott 618344

contents2 Jan. 2017 Mercury prowls the predawn sky

3 Feb. 2017 A blazing ring of fire

4 March 2017 The busiest comet returns to view

5 April 2017 Jupiter rules spring evenings

6 May 2017 The Moon gobbles up a double star

7 June 2017 Saturn’s rings open their widest

8 July 2017 Go deep for distant Pluto

9 Aug. 2017 America’s great coast-to-coast eclipse

10 Sept. 2017 Icy giants swim in the celestial sea

11 Oct. 2017 The Hunter ignites cometary debris

12 Nov. 2017 A stellar year for brilliant Venus

13 Dec. 2017 Winter’s superlative Super Moon

14 2018 Preview Looking ahead to next year . . .

Martin Ratcliffe provides professional planetarium development for Sky-Skan, Inc. Richard Talcott is a senior editor of Astronomy.

A supplement to Astronomy magazine

Sky Guide2017By Martin Ratcliffe

and Richard Talcott

618344

The first total solar eclipse visible from the continental United States in 38 years takes place August 21. Giorgio Massignani

5°

SC ORPIUS

January 19, 30 minutes before sunriseLooking southeast

Saturn

Mercury

OPHIUCHUS

SAGIT TARIUS

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© 2016 Kalmbach Publishing Co. This material may not be reproduced in any form without permission from the publisher. www.Astronomy.com

2 The Moon passes 1.9° north of Venus, 4 a.m. EST

3 The Moon passes 0.2° north of Mars, 2 a.m. EST

Quadrantid meteor shower peaks

7 Pluto is in conjunction with the Sun, 2 a.m. EST

9 The Moon passes 0.4° north of Aldebaran, 10 a.m. EST

12 Venus is at greatest eastern elongation (47°), 8 a.m. EST

Venus passes 0.4° north of Neptune, 9 p.m. EST

14 The Moon passes 0.8° south of Regulus, midnight EST

17 Asteroid Vesta is at opposition, 8 p.m. EST

18 The Moon passes 3° north of Jupiter, midnight EST

19 Mercury is at greatest western elongation (24°), 5 a.m. EST

20 Jupiter passes 4° north of Spica, 4 p.m. EST

24 The Moon passes 4° north of Saturn, 5 a.m. EST

25 The Moon passes 4° north of Mercury, 8 p.m. EST

31 The Moon passes 4° south of Venus, 10 a.m. EST

The Moon passes 2° south of Mars, 8 p.m. EST

S M T W T F S1 2 3 4 6 78 9 10 11 13 14

15 16 17 18 20 2122 23 24 25 26 2829 30 31

Mercury puts on a fine show for Northern Hemisphere

observers on these frigid Janu-ary mornings. At greatest elon-gation on the 19th, it stands 10° above the southeastern horizon 30 minutes before the Sun rises. The innermost planet then shines at magni-tude –0.2, which makes it bright enough to pierce the twilight glow. If you can’t find it with your naked eye, use binoculars to pinpoint its location, and then try to see it without optical aid.

Of course, Mercury is vis-ible for more than a single day. Its altitude a half-hour before sunup remains above 7° from January 5 to 27, while its brightness stays constant at magnitude –0.2 from the 14th through the end of this period. The crisp January mornings also bring nice views of Saturn to Mercury’s upper right. The

gap between these two worlds grows from 8° on January 5 to 21° on the 27th. A pretty wan-ing crescent Moon adds to the twilight scene when it slides 6° above Mercury on the 25th.

Mercury was not named after the winged messenger of Roman mythology for nothing. The inner planet races around the Sun in just 88 days. This rapid movement causes Mercury to swing from the morning to the evening sky and back with a speed unmatched by any other planet.

Not all of these appearances are created equal, however. After Mercury passes on the far side of the Sun in early March, it puts on its finest eve-ning show of the year. At great-est elongation April 1, it shines at magnitude –0.2 and climbs

12° high in the west a half-hour after sunset. Three evenings earlier (on March 29), a slender crescent Moon passes 10° to the planet’s upper left.

Mercury’s next two appari-tions — before dawn in mid-May and after sunset in late July and early August — are the worst of the year for Northern Hemisphere observ-ers. When Mercury returns to view in mid-September’s morning sky, it climbs slightly higher than it did in January. Greatest elongation arrives September 12, when the planet appears 11° high a half-hour before sunrise. The planet then glows at magnitude –0.4 and lies 3° above ruddy Mars (glowing at magnitude 1.8) and 2° below the blue-white star Regulus (magnitude 1.4). Brilliant Venus shines at mag-nitude –3.9 — far brighter than the combined luminosity of the other three objects — and stands 11° above Mercury.

2 Sky Guide 2017

Mercury prowls the predawn sky

Jan2017

The MESSENGER spacecraft revealed Mercury’s dynamic geology (seen here in false color) during a mission that concluded in 2015. Unfortunately, amateur telescopes show the planet as a bland disk. NASA/JHUAPL/CIW

Mercury appears as a bright point of light in morning twilight around its January 19 peak. This is merely the first of several fine apparitions by the inner planet in 2017. All illustrations by Astronomy: Roen Kelly

CIR-PRM-ASY0117_21

B R A Z I L

Rio de Janeiro

CHIL

E

DR CONGO

Sao Paulo

Buenos AiresSantiago

Greatest eclipse

ANGOLA ZAMBIA

SOUTH

AFRICA

PERU

NAM

IBIA

Path of annularity

ARGENTIN

A

A t l a n t i c O ce a n

0 1,500 miles750

0 1,500 km750

2 The Moon passes 3° south of Uranus, 3 a.m. EST

5 The Moon passes 0.2° north of Aldebaran, 5 p.m. EST

10 Penumbral lunar eclipse, 8 p.m. EST

11 The Moon passes 0.8° south of Regulus, 9 a.m. EST

15 The Moon passes 3° north of Jupiter, 10 a.m. EST

17 Venus is at greatest brilliancy, 2 a.m. EST

20 The Moon passes 4° north of Saturn, 6 p.m. EST

23 Jupiter passes 4° north of Spica, 11 a.m. EST

26 Annular solar eclipse, 10 a.m. EST

27 Mars passes 0.6° north of Uranus, 3 a.m. EST

28 The Moon passes 10° south of Venus, 3 p.m. EST

S M T W T F S1 2 4

5 6 7 8 9 1112 13 14 15 16 1719 20 21 22 23 24 25

27 28

T he Moon trans-forms the Sun into a magical ring of fire February 26. Lucky observers

located along a path that stretches from southern South America across the Atlantic Ocean to southwestern Africa can experience this rare event.

A so-called annular solar eclipse doesn’t occur every year (that would be an annual eclipse). The word “annular” derives from the Latin annulus, meaning ring. Such eclipses happen when the Moon passes directly in front of the Sun but is not quite large enough to totally block our star’s brilliant disk. At mideclipse, a dazzling ring of light remains around the Moon’s circular silhouette.

During a total solar eclipse, the Moon completely covers the Sun’s bright disk, and the ghostly light of our star’s outer atmosphere blossoms into view. (Observers in the United States will experience such an eclipse August 21.) But on February 26, the Moon lies far enough from Earth that it

covers about 99 percent of the Sun’s disk.

The eclipse track begins in the South Pacific and makes first landfall on the coast of southern Chile. It then crosses the Andes Mountains before entering the high plateaus of Patagonia in western Argen-tina. Weather prospects here are the best along the entire path, and Patagonia’s gorgeous scenery should serve as a magnet for eclipse chasers. Annularity lasts 65 seconds here. The track then traverses Argentina and departs the continent near the seaside village of Camarones.

Greatest eclipse occurs in the South Atlantic, where annularity lasts 44 seconds. The relatively short duration arises because the Moon cov-ers a maximum of 99.6 per-cent of the Sun’s diameter, and the narrower ring gets extin-guished more quickly.

After crossing the ocean, the path reaches the coast of Angola halfway between Lobito and Namibe, where annularity lasts 69 seconds with the eclipsed Sun 16° above the ocean. The eclipse wraps up at sunset in the southern part of the Demo-cratic Republic of Congo.

Events that can be viewed with the naked eye

Events that can be viewed with binoculars

Events that can be viewed with a telescope

www.Astronomy.com 3

A blazing ring of fire

Feb2017

Moon Phases First Quarter

Full Moon

Last Quarter

New Moon

The path of annularity cuts across southern Chile and Argentina before crossing the Atlantic to the coast of Angola.

February 26 brings an annular solar eclipse for a few lucky viewers. This image shows the end of the January 15, 2010, annular eclipse. Stefan Meyer

1°

36

Path of Comet 2P/Encke

4

March 1

26

2317 20 Feb 14

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26

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The Moon passes 4° south of Mars, 2 p.m. EST

Neptune is in conjunction with the Sun, 10 p.m. EST


6 Mercury is in superior conjunction, 7 p.m. EST

10 The Moon passes 0.8° south of Regulus, 6 p.m. EST

14 The Moon passes 2° north of Jupiter, 4 p.m. EDT

Asteroid Pallas is in conjunction with the Sun, 11 p.m. EDT

20 The Moon passes 3° north of Saturn, 6 a.m. EDT

Equinox (northern spring/southern autumn begins), 6 a.m. EDT

25 Venus is in inferior conjunction, 6 a.m. EDT

26 The Moon passes 0.005° south of Neptune, 4 a.m. EDT

29 The Moon passes 7° south of Mercury, 3 a.m. EDT

30 The Moon passes 5° south of Mars, 9 a.m. EDT

S M T W T F S1 2 3 4

6 7 8 9 10 1113 14 15 16 17 18

19 21 22 23 24 25 26 28 29 30 31

T his should be a great year for comet hunters. Typically, one or two of these dirty

snowballs brightens to 6th magnitude and comes within easy reach of binoculars. But 2017 promises to deliver at least three comets this bright. You can expect these icy visi-tors to appear as fuzzy spheres with short tails.

The first of these guests is Comet 2P/Encke, which comes to the fore in late February and early March. German astrono-mer Johann Encke recognized the object as a periodic comet in 1819, the second comet known to make multiple visits to the Sun’s vicinity (after 1P/Halley). Comet Encke orbits the Sun once every 3.3 years, and the 2017 appearance will be its 63rd observed return.

The comet should glow around 8th magnitude in the evening sky in mid-February. It then lies near Omega (ω)

Piscium, a magnitude 4.0 star located a few degrees west of brilliant Venus. The region lies about 20° high in the west as twilight fades.

While Venus moves away from Omega in February’s second half, Encke loops east and then south of the star. By early March, the comet bright-ens to 6th magnitude as it

passes almost due south of Omega. Encke then lies about 5° high an hour after sunset. The speedy visitor makes its closest approach to the Sun on March 9/10, when it will appear in the field of view of the SOHO spacecraft’s LASCO C3 instrument.

The year’s second binocular comet remains on view all night in late March through the end of April. Comet 41P/Tuttle-Giacobini-Kresak crosses Ursa Major and Draco during this period, when it should reach 5th magnitude. The comet lies near the Big Dipper’s bowl in late March, passing within 1° of Alpha (α) Ursae Majoris on the 27th.

Our third binocular comet should glow at 6th magnitude when it reaches its peak in May and early June. You can find Comet Johnson (C/2015 V2) tracking south through Boötes at this time. Watch for it to pass 5° due east of magni-tude 0.0 Arcturus on June 3.

4 Sky Guide 2017

March2017 The busiest comet returns to view

Comet 2P/Encke sported a slightly greenish head and a long tail when it last returned to the inner solar system in November 2013. Gerald Rhemann

When Comet 2P/Encke returns to the inner solar system in late winter 2017, it loops east and then south against the backdrop of Pisces the Fish.

1°

γ

CIR-PRM-ASY0117_23

Jupiter reachesopposition on April 7

Feb 10March 10

April 10

May 10June 10

VIRGO

N

E

Spica

θ

1 The Moon passes 0.3° north of Aldebaran, 5 a.m. EDT

Mercury is at greatest eastern elongation (19°), 6 a.m. EDT

7 The Moon passes 0.7° south of Regulus, 1 a.m. EDT

Jupiter is at opposition, 6 p.m. EDT


14 Uranus is in conjunction with the Sun, 2 a.m. EDT

16 The Moon passes 3° north of Saturn, 2 p.m. EDT

20 Mercury is in inferior conjunction, 2 a.m. EDT

22 Lyrid meteor shower peaks

The Moon passes 0.2° south of Neptune, 4 p.m. EDT

23 The Moon passes 5° south of Venus, 2 p.m. EDT

28 The Moon passes 6° south of Mars, 4 a.m. EDT

The Moon passes 0.5° north of Aldebaran, 2 p.m. EDT

29 Venus is at greatest brilliancy, midnight EDT

S M T W T F S1

2 4 5 6 7 89 10 12 13 14 15

16 17 18 20 21 2223 24 25 27 28 29

30Jupiter dominates the evening sky this spring. The giant planet reaches oppo-sition and peak vis-

ibility April 7, when it remains up all night and makes its closest approach to Earth for the year. That night it also shines brightest (magnitude –2.5) and looms largest (44" across). Best views come through a telescope.

But the solar system’s big-gest planet is a nighttime fix-ture during most of 2017. It appears in the morning sky from January through opposi-tion, when it transitions to an evening object. Jupiter remains prominent after dusk until it disappears in the Sun’s glow during September. It finally returns to view before dawn in November and December.

At opposition this month, Jupiter rises at sunset and climbs highest in the south around 1 a.m. local daylight time. The brilliant world stands halfway to the zenith at peak elevation. The planet reaches the same elevation due south two hours earlier with each passing month. (In early May, for example, it peaks around 11 p.m. local daylight time.)

Jupiter spends most of the year among the background stars of Virgo the Maiden. In January and February, it lies 4° north of that constellation’s brightest star, 1st-magnitude Spica. Jupiter moves westward as it approaches opposition, passing 0.2° south of 4th-magnitude Theta (θ) Virginis on April 4 and 5. It continues

trekking west until it reaches its stationary point in mid-June some 3° southeast of Gamma (γ) Vir-ginis. Jupiter then embarks on an easterly track, passing 0.6° south of Theta in mid-August and 3° north of Spica in early September.

A telescope reveals impres-sive details in the atmosphere of this gas giant planet. Even the smallest scope shows two dark cloud belts, one on either side of a brighter zone that coincides with the jovian equator. Under good seeing conditions (when turbulence in Earth’s atmosphere dies down and details come into sharp focus), a whole series of alternating belts and zones comes into view. Also watch for the Great Red Spot, a prominent storm in Jupiter’s

southern hemisphere. The best views come when the planet rides high in the sky, typically within two hours of when it reaches peak elevation.

As you observe Jupiter, remember that NASA’s Juno spacecraft is exploring the planet up close. The probe has been returning stunning images and other data from the giant world since it arrived July 4, 2016.

April2017

www.Astronomy.com 5

Jupiter rules spring evenings

The solar system’s largest planet shines brilliantly in spring’s evening sky. It spends most of 2017 in Virgo near that constellation’s brightest star, Spica.

Amateur telescopes show surprising detail in Jupiter’s atmosphere, including the Great Red Spot and several of the bright zones and darker belts seen in this Hubble Space Telescope view. NASA/ESA/A. Simon (GSFC)

A

1°

SAO 98806

CANCER

LEO

Regulus

π

η

ν

π

οω

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ψ

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N

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CIR-PRM-ASY0117_24:

4 The Moon passes 0.5° south of Regulus, 6 a.m. EDT

5 Eta Aquariid meteor shower peaks

7 Mars passes 6° north of Aldebaran, 3 a.m. EDT

The Moon passes 2° north of Jupiter, 5 p.m. EDT

Mercury passes 2° south of Uranus, 7 p.m. EDT


17 Mercury is at greatest western elongation (26°), 7 p.m. EDT


22 The Moon passes 2° south of Venus, 9 a.m. EDT

23 The Moon passes 4° south of Uranus, 1 a.m. EDT

The Moon passes 1.6° south of Mercury, 9 p.m. EDT

26 The Moon passes 5° south of Mars, 10 p.m. EDT

31 The Moon passes 0.3° south of Regulus, 1 p.m. EDT

S M T W T F S1 3 4 5 6

7 8 9 11 12 1314 15 16 17 19 2021 22 23 24 26 2728 29 30 31

dusky gray shadow with a sharp, curved edge slowly creeps up on an unsuspect-

ing star. As you view atten-tively through your telescope, the gap between the shadowy object and the star narrows. Seconds pass, and the star seems to linger as your pulse quickens. Then, suddenly, it’s gone. You’ve just experienced the dark limb of the Moon occulting a star. In one brief moment, you appreciate the closeness of the Moon and the distance to that faraway star.

Among the half-dozen lunar occultations of 7th-magnitude or brighter stars in May, per-haps the most intriguing event occurs on the evening of the 3rd. The Moon is then slightly past its First Quarter phase, and it covers magnitude 6.7 SAO 98806 in Leo at around 9:23 p.m. CDT for observers in the northern United States. (The timing depends on lati-tude and longitude, so set

up early and use the chart below to zero in on the star.) SAO 98806 is a double star, and attentive viewers could see both components disappear. The fainter one glows at 13th magnitude, however, so you’ll likely need an 8-inch or larger scope to see it blink out.

Lunar occultations happen quite frequently as the Moon cruises around the sky in just under a month. Because the

Sun and Earth slightly perturb the Moon’s motion, no two lunar orbits transit the exact same slice of sky. An occulta-tion one month is no guaran-tee that a similar one will occur the following month.

Small amateur telescopes typically will show most lunar occultations of stars brighter than 7th magnitude. The big-gest challenge comes when the Moon is close to Full and its brightness overwhelms a fainter star.

The easiest occultations to observe are those of 1st-magnitude stars, and the Moon sets its sights on both Aldebaran in Taurus and Regulus in Leo this year. For North American viewers, the best events for Aldebaran occur on the evening of March 4 and the morning of September 12, though daylight interferes with the latter one from the eastern half of the continent. The finest occulta-tion of Regulus comes on the morning of October 15.

6 Sky Guide 2017

May The Moon gobbles up a double star

2017

The Moon prepares to occult 3rd-magnitude double star Beta (β) Capri-corni on November 26, 2014. Luna occults a 7th-magnitude pair in May.

Observers in the northern United States can watch the Moon occult the 7th-magnitude double star SAO 98806 on the evening of May 3.

Ala

n D

yer

1°

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OPHIUCHUS

SAGIT TARIUSξ

θ

ο

58

4451

Saturn reaches oppositionon June 15

April 15 May 15 June 15 July 15 Aug 15

N

E

2 Venus passes 1.8° south of Uranus, 11 a.m. EDT

3 Venus is at greatest western elongation (46°), 9 a.m. EDT

The Moon passes 2° north of Jupiter, 8 p.m. EDT

5 Dwarf planet Ceres is in conjunction with the Sun, 8 p.m. EDT


12 Mercury passes 5° north of Aldebaran, 7 a.m. EDT

15 Saturn is at opposition, 6 a.m. EDT


19 The Moon passes 4° south of Uranus, noon EDT

20 The Moon passes 2° south of Venus, 5 p.m. EDT

Solstice (northern summer/southern winter begins), midnight EDT

21 Mercury is in superior conjunction, 10 a.m. EDT


27 The Moon passes 0.03° south of Regulus, 9 p.m. EDT

S M T W T F S2 3

4 5 6 7 8 1011 12 13 14 15 1618 19 20 21 22 2425 26 27 28 29

Show a child the rings of Saturn, and it just might change the trajectory of his or her life. That first

experience can trigger a sense of wonder about the universe that will last forever. And to do this when the weather is warm and Saturn is at its peak, as happens this month, is just icing on the cake.

The ringed planet lies opposite the Sun in our sky June 15, which means that it rises at sunset, climbs highest in the south around 1 a.m. local daylight time, and sets as the Sun comes up. Opposition also brings the planet closest to Earth, so it shines brightest and appears largest when viewed through a telescope.

But you don’t have to wait until June to get acquainted with Saturn. The ringed world begins the year in the morning sky, rising 90 minutes before the Sun. It then lies in the constellation Ophiuchus the Serpent-bearer. It crosses into Sagittarius the Archer in late February and remains there for three months before returning to Ophiuchus in late spring.

2017

www.Astronomy.com 7

Saturn’s rings open their widest

June

B ring. A 4-inch scope also will bring four or five of Saturn’s moons into view.

Following opposition, Saturn continues its westward march. It reaches the end of its so-called retrograde loop in late August at a position 0.8° south of 4th-magnitude Xi (ξ) Ophiuchi. The planet has faded to magnitude 0.4 by then, but it remains conspicu-ous in the early evening sky and a tempting target through telescopes. Saturn remains on view until it disappears in twi-light in late November.

Between January and June, Saturn brightens from magni-tude 0.5 to 0.0. The planet’s yellowish disk measures 18" across at opposition, but few people study the planet’s globe because they can’t take their eyes off the rings. The ring system spans 42" and, more importantly, tips 27° to our line of sight. This is the largest tilt since 2003, and it makes ring structure easier to see than normal. Any telescope will reveal the dark Cassini Division that separates the outer A ring from the brighter

The ringed planet crosses from Sagittarius into Ophiuchus in May as it makes its way toward opposition June 15. The gas giant shines significantly brighter than any of these constellations’ stars.

Saturn’s rings open wider this year than they have since 2003. At opposition in mid-June, they tilt

27° to our line of sight and will look spectacular through

any telescope. NASA/ESA/E. Karkoschka

(University of Arizona)

0.05°

E

CIR-PRM-ASY0117_26

Pluto reaches opposition on July 9/10

July 15

913

17

SAGIT TARIUS

SAO 187913

N

1 The Moon passes 3° north of Jupiter, 3 a.m. EDT

2 Asteroid Juno is at opposition, 9 a.m. EDT

Mercury passes 5° south of Pollux, 8 p.m. EDT


10 Pluto is at opposition, 1 a.m. EDT

13 The Moon passes 0.9° south of Neptune, 2 p.m. EDT

14 Venus passes 3° north of Aldebaran, 7 a.m. EDT

16 The Moon passes 4° south of Uranus, 8 p.m. EDT

19 The Moon passes 0.4° north of Aldebaran, 8 p.m. EDT


25 The Moon passes 0.9° north of Mercury, 5 a.m. EDT

The Moon passes 0.07° north of Regulus, 7 a.m. EDT

26 Mercury passes 1.1° south of Regulus, 5 a.m. EDT

Mars is in conjunction with the Sun, 9 p.m. EDT


30 Mercury is at greatest eastern elongation (27°), 1 a.m. EDT

S M T W T F S1

2 3 4 5 6 7 810 11 12 13 14 1517 18 19 20 21 2224 25 26 27 28 29

31

8 Sky Guide 2017

2017July Go deep for distant Pluto

Pluto skims past a pair of 8th- and 9th-magnitude stars during the second week of July, mak-

ing it relatively easy to find the field of view that harbors this distant world. Even better, Pluto reaches opposition and peak visibility the night of July 9/10, just one day before this close encounter.

Ever since the New Hori-zons spacecraft darted just 7,700 miles above Pluto’s geo-logically active surface on July 14, 2015, amateur astron-omers have shown increased interest in viewing this object. But it’s a challenge: The dwarf planet glows dimly at magni-tude 14.2 at opposition, so you’ll need an 8-inch or larger telescope and a dark-sky observing site to see it directly. On the other hand, if you’re photographically inclined, a digital camera can reach Pluto’s faint magnitude with a fairly short exposure.

The biggest challenge in either case is in finding the correct field of view. That’s why the night of July 10/11 is the one to target. Pluto then nestles near a pair of easy-to-find stars, and the area is vis-ible all night because it lies opposite the Sun in our sky. The two stars reside 1.7° east-southeast of magnitude 2.9 Pi (π) Sagittarii in northeast-ern Sagittarius. The stellar pair — magnitude 8.2 SAO 187913

and its magnitude 9.8 neighbor — stand

37" apart.At 9:30 p.m.

EDT on July 10, Pluto

lies 29" due north of the brighter star. It draws closer to

the fainter companion

during the

course of the night. The planet appears 23" northeast of this star at 12:30 a.m., and just two hours later, the gap shrinks to 16". Pluto passes 7" due north of the star at 6:00 a.m. EDT (3:00 a.m. PDT). Most observ-ers will be able to detect these shifts over an hour or two, and the motion is what confirms the object is Pluto.

This year presents a few other good opportunities to track down this distant world. At the beginning of July, Pluto skims 4' due north of an 8th-magnitude field star. The planet continues to trek west-ward against the stellar back-drop of Sagittarius until late September. On August 31, Pluto passes 3' due south of a 6th-magnitude star located 1° southeast of Pi Sgr. This region then stands highest at the end of evening twilight. The solar system world swings back to this star on the evening of October 24, when it slides 10' to the south.

Pluto’s unexpectedly rugged and diverse terrain stood out to the cameras of the New Horizons spacecraft when it flew

past the world in July 2015. NASA/JHUAPL/SwRI

Pluto treks slowly westward through Sagittarius around opposition. The 14th-magnitude dot slides within 1' of SAO 187913 the night of July 10/11.

Greatest eclipse

Path of totality

CIR-PRM-ASY0117_27

Nashville

St. Louis

Kansas City

Salem

Portland

Carbondale

Casper

Columbia

Columbia

Grand Island

Lincoln

GreenvilleHopkinsville

Idaho Falls

C A N A D A

M E X I C O300 miles

400 km0

0


7 Partial lunar eclipse, 2 p.m. EDT


12 Perseid meteor shower peaks




21 Total solar eclipse, 3 p.m. EDT

Venus passes 7° south of Pollux, 3 p.m. EDT


26 Mercury is in inferior conjunction, 5 p.m. EDT


S M T W T F S1 2 3 4 5

6 8 9 10 11 1213 15 16 17 18 1920 22 23 24 25 2627 28 30 31

2017

www.Astronomy.com 9

AugAmerica’s great coast-to-coast eclipse

The long wait is over. On August 21, a total solar eclipse sweeps across the United States from

Oregon to South Carolina. This is the country’s first glimpse of the Moon’s dark umbral shadow since July 11, 1991, and the first time the mainland has seen totality since February 26, 1979. For tens of millions of people, this will be their first brush with nature’s ultimate spectacle.

To get the best view, you’ll want to position yourself near the eclipse track’s center line. Maximum duration occurs near Carbondale, Illinois, where the Moon completely blocks the Sun’s brilliant disk for 2 minutes and 40 seconds. But even on the coasts, the Sun will disappear for at least two minutes. The Sun’s ethe-real corona — its superheated outer atmosphere — sur-rounds the Moon’s dark sil-houette during those fleeting moments, while a dramatic diamond ring announces both the start and end of totality.

Weather prospects are best along the western part of the track, particularly in Oregon (east of the Cascade Moun-tains), Idaho, Wyoming, and western Nebraska, where observers have a better than 80 percent chance of witness-ing totality. Conditions dete-riorate somewhat over the central United States and even more so during the afternoon hours in the Appalachian Mountains and along the East Coast. Yet climatologists say that even from the eastern

United States, people have at least a 60 percent chance of seeing the Moon hide the Sun. You can increase those chances considerably by keep-ing up with the weather fore-cast and staying mobile.

Observers outside the nar-row track of totality will see a partial eclipse. The Moon cov-ers more than half of the Sun’s diameter across the contigu-ous United States, and our satellite takes at least a bite

from the solar disk every-where in North America. But seeing a partial eclipse is like having tickets to the Super Bowl and then listening to the game on the radio from the stadium parking lot.

Visit www.astronomy.com/eclipse2017 for tips on view-ing the partial phases of the eclipse safely as well as maps showing the eclipse track and circumstances for any location in the country.

Sunlight streams through valleys along the Moon’s limb to create Baily’s beads, a compelling sight immediately before or after totality. Ken Wilson

The path of totality on August 21 crosses the United States from the Oregon coast to the shores of South Carolina.

5 Neptune is at opposition, 1 a.m. EDT

Jupiter passes 3° north of Spica, 7 a.m. EDT



10 Mercury passes 0.6° south of Regulus, 8 a.m. EDT

12 Mercury is at greatest western elongation (18°), 6 a.m. EDT

The Moon passes 0.4° north of Aldebaran, 9 a.m. EDT

16 Mercury passes 0.06° north of Mars, 2 p.m. EDT

17 The Moon passes 0.5° south of Venus, 9 p.m. EDT

18 The Moon passes 0.09° north of Regulus, 1 a.m. EDT

The Moon passes 0.1° north of Mars, 4 p.m. EDT

The Moon passes 0.03° south of Mercury, 7 p.m. EDT

19 Venus passes 0.5° north of Regulus, 7 p.m. EDT


Equinox (northern autumn/southern spring begins), 4 p.m. EDT


Icy giants swim in the celestial sea

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10 Sky Guide 2017

Sept2017

Two giant planets lurk in the frigid outer reaches of our solar system. Although both

Uranus and Neptune possess massive atmospheres, plan-etary scientists refer to them as “ice giants” because their inte-riors harbor much more meth-ane and water vapor than their gas giant siblings, Jupiter and Saturn, where hydrogen and helium dominate.

Both ice giants are on dis-play this fall. Neptune comes to opposition September 4/5, while Uranus reaches the same point October 19. Opposition implies peak visibility, but these planets change so slowly that our view of them stays nearly constant for months. Neptune climbs to magnitude 7.8 in mid-July and stays there until late October. Uranus reaches peak brightness (mag-nitude 5.7) in mid-August and doesn’t budge for four months.

You’ll need binoculars or a telescope to track down

Neptune against the backdrop of Aquarius. For-tunately, there’s a reasonably bright guide star nearby. At opposi-tion, the planet lies 1.2° east of 4th-magnitude Lambda (λ) Aqua-rii. Neptune appears as a point of light through binoculars; hold them steady or mount them on a tripod for the best view. A telescope shows the planet’s 2.4"-diameter blue-gray disk.

After opposition, Neptune moves west-southwest relative to Lambda. The ice giant lies 0.6° southeast of the star dur-ing October’s first week. By late October and early Novem-ber, you can find Neptune 0.6° due south of Lambda.

Uranus appears seven times brighter than Neptune. In fact,

it reflects enough light in our direction that it shows up eas-ily through binoculars and even to the naked eye from under a dark sky. It resides one constellation east of Aquarius in Pisces the Fish.

If you want to view Uranus well before opposition, target it the morning of June 2. The planet then appears as a 6th-magnitude “star” 1.8° north of brilliant Venus. Binoculars will capture both objects as well as 4th-magnitude Omicron (ο) Piscium to the pair’s east.

Omicron will serve as your guide to Uranus the rest of the year. From late July through August, the ice giant appears 1.1° north of this star. By oppo-sition in mid-October, the planet lies 1.8° west-northwest of Omicron. A telescope can confirm a sighting of Uranus by showing its distinctive blue-green disk, which spans 3.7".

1°

CIR-PRM-ASY0117_28

AQUARIUS

τ

φ

χ

ψ1

ψ2

ψ3

λ

κ

σ

Neptune

N

E

Amateur telescopes reveal Neptune’s tiny disk and blue-gray color. The giant planet appeared far more dramatic to the cameras aboard the Voyager 2 probe during its 1989 flyby. NASA/JPL

Neptune appears against the background stars of Aquarius this year. At opposition on the night of September 4/5, the magnitude 7.8 planet lies 1.2° east of 4th-magnitude Lambda (λ) Aquarii.


5 Venus passes 0.2° north of Mars, 9 a.m. EDT

6 The Moon passes 4° south of Uranus, noon EDT

8 Mercury is in superior conjunction, 5 p.m. EDT

9 The Moon passes 0.6° north of Aldebaran, 3 p.m. EDT

15 The Moon passes 0.2° north of Regulus, 7 a.m. EDT

17 The Moon passes 1.8° north of Mars, 6 a.m. EDT

The Moon passes 2° north of Venus, 8 p.m. EDT

19 Uranus is at opposition, 2 p.m. EDT

21 Orionid meteor shower peaks


26 Jupiter is in conjunction with the Sun, 2 p.m. EDT

28 Asteroid Pallas is at opposition, 8 p.m. EDT


The Hunter ignites cometary debris

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Oct2017

Comet 1P/Halley has had a power-ful impact on astronomy over the centuries. Its

return to the inner solar sys-tem every 75.3 years creates a spectacle in Earth’s sky that has inspired countless sky-watchers. And when English astronomer Edmond Halley first deduced the comet’s periodic nature in 1705, he showed that these icy visitors follow the laws of physics laid down a few decades earlier by his friend Isaac Newton.

But Comet Halley reminds us of its presence every year. Each time the comet passes near the Sun, it sheds tons of dusty debris. And every October, Earth slams into this rubble. Friction with our atmosphere incinerates the dust particles at altitudes between 50 and 70 miles, pro-ducing luminous trails of incandescence known as meteors. All of these streaks appear to radiate from the constellation Orion the Hunter, so the event is called the Orionid meteor shower.

This year, the shower peaks before dawn October 21, just two days after New Moon. This creates ideal conditions for meteor viewing. Observers under a dark sky can expect to see up to 20 meteors per hour when the radiant — which lies near the Hunter’s right elbow — climbs highest around 5 a.m. local daylight time.

The Orionids prove to be a harbinger of great meteor showers in the closing months of 2017. The Leonids in mid-

November also coincide with a New Moon and should pro-duce approximately 10 mete-ors per hour. But both of these displays are only warmups for the best shower of the year: the December Geminids. This shower peaks the morning of the 14th under a waning cres-cent Moon that won’t hinder viewing at all. Observers under a dark sky can expect to see up to 120 meteors per

hour — two a minute, on average — at the shower’s best.

The Quadrantid shower in early January should be nearly as good. It also produces about 120 meteors per hour, and this year it peaks under a waxing crescent Moon that sets before midnight. Unfortunately, August’s Perseid shower shares the sky with a waning gibbous Moon, which will drown out many of the fainter meteors.

Meteor showers in 2017Name Peak date Moon’s phase ProspectsQuadrantids Jan. 3 Waxing crescent Good Lyrids April 22 Waning crescent Good Eta Aquariids May 5 Waxing gibbous Fair Perseids Aug. 12 Waning gibbous Poor Orionids Oct. 21 New Moon Excellent Leonids Nov. 17 New Moon Excellent Geminids Dec. 14 Waning crescent Excellent

An Orionid meteor streaks to the left of Orion’s Belt and the glowing gas of the Orion Nebula in this view of the 2012 shower. Tony Rowell

1 Venus passes 4° north of Spica, 11 a.m. EDT

2 The Moon passes 4° south of Uranus, 9 p.m. EDT


11 The Moon passes 0.4° north of Regulus, noon EST

12 Mercury passes 2° north of Antares, 10 a.m. EST

13 Venus passes 0.3° north of Jupiter, 1 a.m. EST

14 The Moon passes 3° north of Mars, 8 p.m. EST

16 The Moon passes 4° north of Jupiter, 4 p.m. EST

17 Leonid meteor shower peaks

20 The Moon passes 7° north of Mercury, 4 a.m. EST

The Moon passes 3° north of Saturn, 7 p.m. EST

23 Mercury is at greatest eastern elongation (22°), 7 p.m. EST

26 The Moon passes 1.2° south of Neptune, midnight EST

27 Mars passes 3° north of Spica, 7 p.m. EST

28 Mercury passes 3° south of Saturn, 4 a.m. EST


A stellar year for brilliant Venus

CIR-PRM-ASY0117_29

November 13, 30 minutes before sunriseLooking east-southeast

LIBR A

VIRGO

Spica

JupiterVenus

5°

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12 Sky Guide 2017

Nov2017

For all except 10 days during the first 11 months of 2017, Venus appears strik-ing in either the

evening or morning sky. The planet’s dazzling performance winds down in November, but not before a stunning final act. Shortly before dawn on the 13th, Venus passes within a Full Moon’s width of Jupiter — an event sure to capture the attention of novices and sea-soned observers alike.

More on that in a minute, but first let’s see what Venus has in store for us the rest of the year. The inner world begins 2017 as a beacon in the southwest after sunset. At greatest elongation January 12, Venus lies 47° east of the Sun and stands 30° above the hori-zon an hour after sunset. The planet gleams at magnitude –4.5, far brighter than any other point of light in the sky.

Venus pretty much main-tains this altitude for another

month before it starts plunging toward the western horizon. It remains on view until the solar glare swallows it around March 21. The inner planet swings between the Sun and Earth on the 25th and then shoots into view before dawn at month’s end.

Morning apparitions in spring aren’t as favorable as evening ones, however, and Venus doesn’t climb as high at dawn as it did at dusk earlier in the year. At greatest elongation June 3, it appears 12° high in the east an hour before sunrise. You’ll have no problem identi-fying it, however — the magni-tude –4.4 planet still dominates the sky. Venus moves higher as summer turns to fall. On Sep-tember 1, you can find it nearly 20° above the eastern horizon an hour before sunup.

As November begins, Venus appears only in twilight. Jupiter, which passed behind the Sun in late October, rises 20 minutes before our star. As

they approach their conjunc-tion, you can see the planets’ relative positions shift from one day to the next. You might consider photographing the changing scene. The best images should include some interesting foreground objects silhouetted against the colorful twilight sky.

On November 13, the pair rises together in the east-southeast some 70 minutes before the Sun and climbs 5° high a half-hour later. Venus, at magnitude –3.9, appears just 0.3° to the left of magnitude –1.7 Jupiter. A telescope cap-tures both in a single field. Venus appears 10" across, and Jupiter — with its four bright moons nearby — spans 31".

Although Venus can pass directly in front of Jupiter, this is truly a once-in-a-lifetime event. Such an occultation hasn’t happened since January 3, 1818, and won’t again until November 22, 2065.

Brilliant Venus slides 0.3° to the left of Jupiter as twilight paints the sky the morning of November 13.

Venus (lower right) passed within 0.5° of Jupiter on June 30, 2015. The two have an equally close conjunction before dawn November 13. Steve Irvine

3 The Moon passes 0.8° north of Aldebaran, 8 a.m. EST

8 The Moon passes 0.7° north of Regulus, 6 p.m. EST

12 Mercury is in inferior conjunction, 9 p.m. EST

13 The Moon passes 4° north of Mars, 11 a.m. EST

14 Geminid meteor shower peaks

The Moon passes 4° north of Jupiter, 9 a.m. EST

21 Solstice (northern winter/southern summer begins), 11 a.m. EST

Saturn is in conjunction with the Sun, 4 p.m. EST

24 The Moon passes 1.4° south of Neptune, 8 a.m. EST

27 The Moon passes 5° south of Uranus, 1 p.m. EST


Winter’s superlative Super Moon

10°

December 3, 8 P.M.Looking east

CIR-PRM-ASY0117_30

GEMINI

AURIGA

TAURUS

ORION

Capella

Aldebaran

Moon

RigelBetelgeuseCastor

Pollux

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www.Astronomy.com 13

2017Dec

You’ll likely hear a lot about the December 3 Full Moon. That’s because it occurs

near perigee, our satellite’s closest point to Earth in its monthly orbit. Full Moon arrives at 10:47 a.m. EST on the 3rd, and perigee comes 17 hours later, at 3:46 a.m. on the 4th. That makes this the closest Full Moon of 2017 and also the biggest.

How much closer and big-ger? December’s Full Moon comes within 222,440 miles of Earth. The farthest Full Moon of 2017 occurs June 9, when 252,446 miles separate our two worlds. That’s a 13.5 percent difference, and it translates into a 13.5 percent change in size, from 29.40' in June to 33.37' in December.

While these changes are not insignificant, they are at best barely perceptible. Human memory can’t com-pare Luna’s size from one night to the next, much less from dates a couple of months apart. Photographs are the best way to see the change. Simply image the two Full Moons with the same photo-graphic setup, and the differ-ence will be obvious.

As Internet and media hype build for the December 3 Full Moon, you can expect the phrase “Super Moon” to be shared on social media faster than people can explain what it means. Astronomy enthu-siasts split into two camps. One group considers the term nothing more than hype and disdainfully declares that its

origin lies in astrology and not astronomy. The other realizes that the term’s wide-spread use can encourage ordinary people to view the Moon, and it provides a golden opportunity to pro-mote a deeper understanding and interest in astronomy.

Of course, astronomers view every Full Moon as super — at least in the sense that it always grabs lots of attention, particularly as it rises and hangs just above the horizon. On the evening of December 3, the Full Moon comes up around 5 p.m. local time along with the bright stars of Taurus the Bull. The dramatic scene an hour or two after moonrise includes 1st-magnitude Aldebaran to the Moon’s upper right and the blazing stars of Orion the Hunter ris-ing below.

No doubt many people will notice that the Moon looks unusually large near the hori-zon. This is just an illusion, however. Seeing the Moon juxtaposed with a familiar landscape fools the mind into thinking it’s bigger. In fact, the Moon lies one Earth radius farther away, and thus is slightly smaller, when it lies near the horizon than when it stands overhead.

December’s Full Moon appears against the background stars of eastern Taurus, just above the glittering luminaries of Orion the Hunter.

The September 27, 2015, Super Moon looms over the landscape. A similarly large Full Moon awaits observers December 3. Jamie Cooper

2018 previewLooking ahead to next year...

14 Sky Guide 2017

It’s hard to imagine that the observing highlights of 2018 can compare with this year’s spectacular array of events, at least not when you have the August 21 total solar eclipse tip-ping the scales in 2017’s favor. But don’t despair — 2018 will offer its own rewards.

The top event for most observers will be their finest views of Mars in 15 years. When the Red Planet reaches opposition the night of July 26/27, it will shine at magnitude –2.8 and appear 24.3" across when viewed through a telescope. Both marks are the best since its historic close approach in August 2003.

Mars will exceed magnitude –1.0 from late May until mid-October and span greater than 10" from late April until mid-November. Although the ruddy world won’t climb high for observers at mid-northern latitudes — it spends its peak among the background stars of Capricornus — it still puts on a stunning show.

Mars certainly will garner the lion’s share of attention, but planet observers will have plenty of other options. Venus will shine brilliantly in the western sky after sunset throughout the

summer months. Meanwhile, Jupiter will reach its peak in early May, and Saturn will follow in late June.

Although solar eclipse chasers have little to look forward to in 2018 — despite there being three of them, all are partials and none is visible from the United States — most people won’t have to travel to see the year’s finest eclipse. The evening of Jan-uary 31 brings the first total eclipse of the Moon since Septem-ber 2015. Observers across the western two-thirds of North America will see at least part of the total phase while the rest will see the eclipse’s initial partial phases.

Meteor observers also should anticipate 2018. The Perseid shower in August will peak within a day of New Moon, provid-ing dark skies throughout the night. And the equally prolific Geminids in December will reach maximum under a waxing crescent Moon that will offer only minimal interference.

The year will wrap up with a comet that could reach naked-eye visibility. Comet 46P/Wirtanen will sweep within 7 million miles of Earth in December and likely will reach 5th magnitude — and possibly 3rd magnitude — as it tracks through Taurus.

Mars will shine brilliantly and loom large through telescopes in 2018 as it puts on its best performance since 2003. ESA/MPS/OSIRIS Team

The first total lunar eclipse since 2015 will grace the skies above North America after sunset January 31, 2018. Randy Brewer

Comet 46P/Wirtanen appeared near the Flaming Star Nebula (IC 405) in 2008. It will return to Earth’s vicinity in December 2018. John Chumack

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