Sky & Telescope - USA (2020-01)

chemical handwarmers around your
lens and intervalometer. In an hour’s
time you will have tallied more than
100 images without even trying. Later,
when you’re indoors, you can swipe
the frost off the camera back and click
through your take to fi nd (we hope!) a
treasure or two.
Because the radiant lies at a declina-
tion of 50° north, it’s circumpolar from
many North American locations and

visible all night. Be alert for Quadrantid

earthgrazers, meteors that climb upward

from the northern horizon and glow for

many seconds as they skim the top of

the atmosphere.

Unlike many meteor showers that

originate from dust and debris sloughed

off by passing comets, the Quads’

parent body appears to be an extinct

near-Earth comet discovered in 2003

called 2003 EH 1. Peter Jenniskens,

skyandtelescope.com • JANUARY 2020 49

an American astronomer and meteor

researcher, has proposed that the

Quadrantid stream evolved from the

breakup of a much larger comet nucleus

of which 2003 EH 1 is a remaining frag-

ment (https://is.gd/2003EH1). Because

the debris stream is narrow and Earth

encounters the stream perpendicularly,

the planet zips through the densest

meteoroid braids in hours, which is why

the peak is so brief.

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Jan 3

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23

Hot Rocks for Cold Nights

TWO BRIGHT ASTEROIDS ply the eve-

ning sky this month — 5 Astraea and

511 Davida. Davida reaches opposi-

tion on January 15th in Gemini and

Astraea on the 21st in Cancer. Both

shine around 9th magnitude and are

glimpsable in binoculars from dark

skies, but most of us will fi nd a small

telescope better suited to the task.

Astraea, a large stony asteroid about

119 kilometers across, starts the month

at magnitude 9.5, brightens to 8.9 at

opposition and fades to 9.3 by month’s

end. Astraea was the fi fth asteroid

discovered after the familiar foursome

of Ceres, Pallas, Juno, and Vesta. Those

fi rst discoveries came one after another

between 1801

and 1807. Then

38 years went by

without a single

new object found.

Many astrono-

mers assumed

that was all she

wrote until Karl

Ludwig Hencke, a

German amateur,

spotted a fi fth

on December 8, 1845, after searching

steadfastly for 15 years with a small

achromatic refractor.

On the night of his discovery Hencke

assumed the new object was a variable

star since he’d swept the region many

times before. He sent off an account of

his new fi nd to a Berlin newspaper. Sev-

eral days later, Johann Encke of Encke’s

Comet fame, confi rmed the object as a

new “planet” after having observed it

move against the fi xed stars. Two years

later, Hencke discovered his second

asteroid, 6 Hebe.

These two almost back-to-back fi nds

reenergized astronomers to begin hunt-

ing anew for asteroids. In the coming

uThe tick marks

represent 0h UT; for

North America, this

time falls in the early

evening (or late after-

noon) of the previous

date. The chart for

Davida traces the

asteroid’s path one

week prior to and one

week after opposition.

years, what had been a trickle of new

objects became a torrent. In fact, so

many new asteroids were discovered

that astronomers abandoned calling

them planets — the popular term at the

time — and settled instead on asteroid,

a word meaning “starlike.” One man’s

persistence had paid off — Hencke

unintentionally revolutionized our

understanding of asteroids as minor

solar system bodies compared to the

more massive planets.

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MINOR

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GEMINI

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Dec 1, 2019

Jan 1, 2020

Mar 1

Jan 1, 2020

Feb 1

Apr 1

Mar 1

Feb 1

Apr 1

Dec 1, 2019

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