Astronomy - 06.2019

BINOCULARUNIVERSE

BY PHIL HARRINGTON

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ARIES

CETUS

TAURUS

Path of Vesta

Oct 21

31

Nov 10

20 30 Dec^10

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OPHIUCHUS

SCORPIUS

LIBRA

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Path of Ceres

May 12 22

June 1 11

21

July 1

11

21

31

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14 ASTRONOMY • JUNE 2019

O

n January 1, 1801,

Italian astrono-

mer Giuseppe

Piazzi spotted a

“star” through his

telescope that was not on his

detailed charts of the region. He

returned to the same location

over the next few nights, only to

find that this new star couldn’t

be a star at all. It had moved

against the stationary backdrop.

Whatever he had discovered, it

had to be orbiting the Sun.

At first, he thought he had

discovered a comet, but later

observations (by him and oth-

ers) allowed an orbit to be cal-

culated. Piazzi’s new object was

revolving around the Sun in a

nearly circular orbit at a dis-

tance of 2.77 astronomical

units. (An AU is the average

Earth-Sun distance.) That

placed it in the gulf between

Mars and Jupiter. He had dis-

covered the first asteroid, now

reclassified as a dwarf planet by

the International Astronomical

Union. As is customary, the

discoverer of a new member of

the solar system has the honor

of naming it. Piazzi chose

Ceres for the Roman and

Sicilian goddess of grain.

Asteroids can change dra-

matically in brightness depend-

ing on their distance from

Earth. The best time to look for

them is when their distance

away from us is minimal. This

occurs at opposition, when the

asteroid rises in the east as the

Sun sets in the west.

June opens with Ceres just

past its May 28 opposition.

From late May through early

July, it appears to move in ret-

rograde as quicker Earth passes

by. During this time, it slides

from Ophiuchus, through

northernmost Scorpius, and

into Libra. Throughout, it will

remain around 7th magnitude.

Of course, that region of the

sky has lots of 7th-magnitude

stars, so spotting which one is

Ceres is a bit like looking for a

celestial needle in a haystack.

Ceres moves past several

notable stars during the month,

which should help in our quest.

I hope the sky is clear for you

May 24 and 25. On those

nights, Ceres is just north

of 4th-magnitude Chi (χ)

Ophiuchi. As it continues to

march westward, it passes 1.5°

north of 4th-magnitude Nu (ν)

Scorpii on June 9, and on the

17th, it appears 1.6° north of

Graffias (Beta [β] Scorpii).

During July, its retrograde

motion will slow, allowing

Ceres to resume its normal,

easterly track. It will hover

between Graffias and Lambda

(λ) Librae, slowly arcing south,

then southeast by the end of the

month. In the process, Ceres

will fade by more than a magni-

tude since June 1.

Once you spot Ceres, make

visiting it a habit over the next

few months. Note its position

on the chart each time you

glimpse it. In the end, you’ll

have a personal record of Ceres’

2019 apparition.

Ceres is not the only member

of the asteroid belt visible

through your binoculars. More

than 60 become brighter than

10th magnitude around opposi-

tion, and should therefore be

visible through binoculars.

On August 13, the 15th aster-

oid discovered, Eunomia, will

reach opposition. That night, it

will shine at magnitude 8.2,

faint but doable through

steadily supported 50mm bin-

oculars. It will lie among the

faint stars of Aquarius, 3.7° west

of Sadalsuud [Beta Aquarii].

You’ll need a good finder chart

to locate this challenging target.

(More on that later.)

Surprisingly, even though

Ceres is the largest object in the

asteroid belt at about 600 miles

(960 kilometers) across, it is not

the brightest. That honor goes

to Vesta, the fourth asteroid

discovered. German physician

Heinrich Olbers found Vesta on

March 29, 1807. Olbers had also

discovered the asteroid Pallas

five years earlier.

Vesta always puts on a fine

show around opposition. That’s

next set to occur November 12.

At that time, Vesta will be

within the constellation Cetus

the Whale. At opposition, Vesta

will be 1.56 AU from Earth and

shine at magnitude 6.5. It will

be 1.9° west-southwest of 4th-

magnitude Omicron (ο) Tauri,

which marks one of the Bull’s

front hoofs. That night’s Full

Moon will be only about a bin-

ocular field away, confounding

efforts to see Vesta. But take

heart. Vesta stays bright several

weeks before and after opposi-

tion: In November, it remains

brighter than 7th magnitude

and within binocular range.

I mentioned earlier that

Eunomia would be challenging

to search for, and the same is

true of most asteroids — accu-

rate finder charts are a must.

One of the best online resources

for this is in-the-sky.org/

newsindex.php?feed=asteroids.

Good luck with this introduc-

tion to asteroiding.

I’d enjoy hearing your

results. Contact me through my

website, philharrington.net.

Until next month, remember

that two eyes are better than

one.

Let’s go

asteroiding!

Minor planets make for challenging binocular targets.

Ceres crosses into Ophiuchus, Scorpius, and Libra from late May through early July.

Vesta remains bright weeks before and after the asteroid’s opposition November 12.

Phil Harrington is a longtime

contributor to Astronomy and

ASTRONOMY the author of many books.

: ROEN KELLY

ASTRONOMY

: ROEN KELLY