Australian Sky & Telescope - May 2018

44 AUSTRALIAN SKY & TELESCOPE May | June 2018

UNDER THE STARS by Fred Schaaf

In the path of the

closest comet

T

hirty-five years ago, some of the

best weather in the world helped

me to experience a prodigious

wonder that most skygazers missed.

It was the nearest pass to Earth of a

comet in over 200 years. The marvel

was Comet IRAS-Araki-Alcock (Comet

I-A-A), discovered first by the Infrared

Astronomical Satellite and then

independently by amateur astronomers

Genichi Araki in Japan and George

Alcock (with binoculars, looking out a

window) in England.

I spent six nights in the Northern

Hemisphere following this intrinsically

dim comet through ever brighter and

bigger forms as it hurtled less than 4.8

million kilometres from Earth. Its path

across the stars on those nights is one

I’ll never forget — and one which I’d like

to explore in its own right here in this

column.

First night: Naked eye past

Draco’s head. “My search with binocs

immediately produced a prominent ball

of fuzzy light in its still imperceptibly

slow roll past the head of the celestial

dragon,” I wrote in my book Comet of

the Century (Copernicus Books, 1996).

When I first spotted Comet I-A-A, it

was a roughly magnitude-4.9 object

detectable with the naked eye, with

a 15′ patch of coma visible through a

15-cm telescope.

The circumpolar head of Draco

doesn’t get highest in the north until

the middle of the night in May, but was

already prominent in the northeast

in the evening. The Dragon’s head

points toward ascending Vega and

the Keystone of Hercules. It consists

of stars of 2nd, 3rd, 4th and 5th

magnitude: Gamma (γ) Draconis

(Eltanin), Beta (β) Draconis (Rastaban),

Xi (ξ) Draconis (Grumium), and Nu

(ν) Draconis (Kuma). Eltanin, at 2nd

magnitude, is the orange eye of Draco.

And 5th-magnitude Kuma is formed

by equally bright white components a

generous 62′′ apart.

Third night: A Great Orion Nebula

in the body of Draco. “Last torn cloud

curtain edge was withdrawn to reveal

a sky clean and sheer to about mag. 7.0

at its summit... and a handful of strong

phosphorescence hung in mid-flight on

that sky’s north shoulder.” The comet

was in the long, twisting body of Draco,

which wraps around the North Ecliptic

Pole, near which glows NGC 6543, the

wonderful 9th-magnitude Cat’s Eye

Nebula. But that night Comet I-A-A

appeared larger and much brighter

than M8, the Lagoon Nebula, like a

detached piece of Milky Way, “... or at

least for me in that magic clear dark

— like another Orion Nebula in size,

brightness and even shape!”

Fourth night: Flung from the

Little Dipper’s bowl. At nightfall the

comet’s coma was already surrounding

Kochab, Beta (β) Ursae Majoris. “It was

fascinating viewing the rather bright

star cloaked in that slight veil, and

the conjunction of the comet’s centre

with the star was surprisingly close.”

The comet was going so fast it only

took minutes for it to move off this

underappreciated orange ‘Guardian of

the Pole’ that’s very nearly as bright as

Polaris. It was seemingly being flung,

in one day, from the Little Dipper’s

bowl to just past the Big Dipper’s bowl.

I judged the comet to be magnitude 2.8

or 2.9 and 1° to 1¼° wide to the naked

eye that night.

Sixth night: A huge, near-1st-

magnitude comet passes M44. The

head of the comet was very close to the

smaller, much dimmer patch of Messier

44 (the magnitude-3.1 and 1½°-wide

Beehive Cluster). Comet authority

John Bortle rated the comet’s head as

magnitude 1.7 and at least 2° wide

that evening. Walter Scott Houston

estimated the comet’s head as an

astounding 6° across! And, in a sky so

dark and clear I could trace the zodiacal

light bridge across it, I saw the two

edges of the previously tailless comet’s

tail extending up to 15° long.

„FRED SCHAAF saw his irst naked-eye

comet, Tago-Sato-Kosaka, in 1970. AURA / KPNO

From Draco to Cancer a comet hurtled.