Australian Sky & Telescope - April 2018

44 AUSTRALIAN SKY & TELESCOPE April 2018

The great Overdog,

That heavenly beast

Withastarinoneeye,

Gives a leap in the east.

He dances upright

Allthewaytothewest

And never once drops

Onhisforefeettorest.

I’m a poor underdog,

ButtonightIwillbark

With the great Overdog

That romps through the dark.

—Robert Frost, “Canis Major”

T

he first serious poem I ever recall

being read to me and discussed

was Robert Frost’s “Stopping by

the Woods on a Snowy Evening”. I

think I was only five years old at the

time, but it certainly made a great

impression on me. A few more years

passed before I, already a budding

stargazer, first had the pleasure of

coming across one of Frost’s other

poems, “Canis Major”. Strangely, I don’t

remember ever quoting it in any of my

astronomical writings. I’m finally doing

it now, however, and for a good reason:

an exploration and celebration of this

constellation of the Big Dog that at

times I’ve found to be a bit neglected.

Surely Sirius, by far the most

brilliant star in the night sky, steals

a lot of attention away from the rest

of its constellation. But Canis Major

features four other stars

brighter than magnitude

2.5. One of those four is

occasionally even included in

the ranks of 1st-magnitude

stars — though as the least

bright 1st-magnitude star. It’s far

more often considered to be the

brightest of the 2nd-magnitude class.

I’m speaking of Adhara, which at

In the southern part of the

Canis Major constellation, at the

opposite end from Sirius, shines this

compact triangle. It’s composed of

1.5-magnitude Epsilon (ε)Canis

Majoris (Adhara), 1.8-magnitude

Delta (δ) Canis Majoris (Wezen) and

2.5-magnitude Eta (η) Canis Majoris

(Aludra).IcallittheSouthernCanis

Triangle.And,remarkably,these

stars’ brightnesses closely rival those

ofthethreestarsinOrion’sBelt:

1.7 (Alnilam), 1.7 (Alnitak) and 2.3

(Mintaka). Orion’s Belt straddles the

celestial equator and therefore sparkles

high above the northern horizon

when on the meridian for observers at

southern temperate latitudes.

The three stars of the

Southern Canis Triangle are

mighty suns. At distances

of 405 light-years (Adhara), about

1,800 light-years (Wezen), and possibly

about 3,000 light-years (Aludra), the

absolute magnitudes of these stars are

around –4, –7 and –7.5. James Kaler’s

wonderful ‘Stars’ website (https://

is.gd/kalerstars) tells us that Wezen

is cooler than the other two stars; it’s

a rare yellow supergiant that in less

than 100,000 years should become a

red supergiant somewhat like Antares.

Kaler also notes that Aludra is probably

only about 12 million years

old, and that if our eyes were

sensitive to ultraviolet light,

Adhara would shine brighter than

any other star in our sky.

„FRED SCHAAF’s first book,

Wonders of the Sky (Dover Publications),

was published about 35 years ago.

UNDER THE STARS by Fred Schaaf

The great Overdog and its pack

Sirius isn’t the only star that shines brightly in Canis Major.

magnitude 1.5 is the 22nd brightest star

in all the sky. Adhara slightly outshines

the far more famous Castor. Castor

can ascribe its greater fame largely

to being in a zodiac constellation,

Gemini. Of course, its biggest source

of renown is being one of the pair of

‘twin’ luminaries of Gemini, the Twins,

the other being Pollux. But, as I’ve

argued before, Adhara is actually part

of a starry trio, not duo, which is quite

impressive in its own right.

“If our eyes were sensitive to ultraviolet light, Adhara

would shine brighter than any other star in our sky.”

LIBRARY OF CONGRESS / RESTORATION: ADAM CUERDEN