Page 68 - Astronomy - October 2017 USA

BINOCULARUNIVERSE

BY PHIL HARRINGTON

Exploring

Capricornus

The dazzling globular star cluster M30 glows at 7th magnitude and is
Two double stars and a great globular the finest deep-sky object in the constellation Capricornus. DANIEL VERSCHATSE
cluster highlight this dim star group. Beta Capricorni consists of an unequal pair of 3rd- and 6th-magnitude suns that
float together in this sketch made with a 6-inch f/8 reflector at 240x. JEREMY PEREZ
apricornus the Sea In October’s evening sky, we space. The yellow giant south- (ζ) Capricorni. Center Zeta in
2
Goat is one of the find Capricornus fin-deep in eastern star, known as Alpha , your binoculars, and then look
faintest constella- the area of sky known as the is 109 light-years from us, while toward the eastern edge of the
1
tions along the eclip- “wet quarter.” There, we see Alpha , a yellow supergiant, is field. A 5th-magnitude star, 41
Ctic. With none of its several constellations that are nearly seven times farther away. Capricorni, should just be com-
stars shining brighter than 3rd associated with water in one The second star, Dabih or ing into view. Hold on 41, and
magnitude, many suburban star- way or another. Besides Beta (β) Capricorni, is just 2° then glance just to its west. Can
gazers often bypass it in favor of Capricornus, there’s Aquarius south of Algedi. It easily fits you see a dim, round patch of
brighter regions. Yet for those the Water-bearer; Piscis into the same field of view. grayish light surrounding a
who persevere, Capricornus Austrinus the Southern Fish; While Algedi’s two stars appear brighter core? That’s M30.
holds a few hidden gems visible Cetus the Whale; and Pisces the identically bright, Dabih’s two- Messier discovered M30
through our binoculars. Fish. You may need to travel to a some looks noticeably different. the night of August 3, 1764.
So, what exactly is a Sea site that is free of light pollution The brighter sun, called Dabih- Like most globulars in his cata-
Goat, and who concocted and horizon-hugging haze to Major, shines at 3rd magnitude, log, it was described as a round
that image? Despite its faint- make them out, since faint stars while its companion, Dabih- nebula free of any stars. How
ness, Capricornus is one of comprise nearly all of them. Minor, is 16 times fainter at 6th wrong he was. We now know
the oldest constellations in Binoculars, however, come to magnitude. Both form a physi- that faint patch is actually a
the sky, tracing its origin back our rescue when viewing under cal system 330 light-years away, swarm of 100,000 or so indi-
to ancient Sumeria. As one less-than-ideal circumstances. with each separated from the vidual suns lying an estimated
culture was assimilated into Begin by drawing an imaginary other by about a third of a light- 27,100 light-years away. But
another, Capricornus became line from Vega southeastward year. It takes approximately unlike most globulars associ-
associated with Pan, the Greek to Altair, and then keep going 700,000 years for the pair to ated with our galaxy, M30
god of nature who was half about an equal distance farther. orbit one another. appears to be orbiting through
goat and half human. In one The area may look barren by There is much more to Dabih the Milky Way’s inner galactic
tale, Pan helped Zeus battle the eye, but aim your binoculars than meets the eye. Studies halo backward, or in retro-
Titans. During an especially there and you should spot two show that both stars are them- grade. This suggests that,
harrowing part of the clash, conspicuous stars separated by selves accompanied by fainter unlike most other globulars, it
Pan barely escaped Typhon, about 2°. Both lie at the north- companions unseen through may have been stolen from a
the deadliest creature in Greek western corner of Capricornus’ binoculars. Dabih is at least a satellite galaxy rather than
mythology, by giving himself a triangular form. quintuple system. having been formed from the
fish’s tail and jumping into the Let’s first examine the north- Our final stop within protogalactic cloud that begat
Nile River. ernmost of those stars, Algedi, Capricornus is the Sea Goat’s the Milky Way.
or Alpha (α) Capricorni. sole contribution to the Messier Do you have a favorite bin-
Algedi is made up of two 4th- catalog. The 7th-magnitude ocular object? I’d love to hear
magnitude suns that are easy globular cluster M30 lies in about it and feature your
to resolve with the smallest the constellation’s barren observations in future col-
pocket binocular, and even southeastern corner. To find umns. Drop me a line through
with the unaided eye given dark it, slowly scan eastward from my website, philharrington.net.
skies. They look like heavenly Algedi along the top side of the Until next month, remember
headlights spaced 6' apart. But Capricornus triangle to Deneb that two eyes are better than
looks can be deceiving. It turns Algedi (Delta [δ] Capricorni) one.
out the pair is strictly a chance, at the triangle’s eastern corner.
line-of-sight coincidence. Algedi Now, shift 8°, or a little more Phil Harrington is a longtime
is a so-called “optical double,” than a typical binocular field, contributor to Astronomy and
Alpha Capricorni’s twin 4th-magnitude
stars are visible in this sketch made with two stars that are actually to the southwest. There you the author of many books.
nowhere near each other in should see 4th-magnitude Zeta
a 6-inch f/8 reflector at 240x. JEREMY PEREZ

68 ASTRONOMY • OCTOBER 2017