Some Light Science Reading. The Constellations: Canes Venatici

As first appeared in the March 2010 edition of the Syracuse Astronomical Society newsletter The Astronomical Chronicle (PDF).

Constellation Map generated with Starry Night Pro 6.

It often seems to me that the night is much more alive and richly colored than the day.
Vincent van Gogh to his brother Theo, 1888

If the Hubble Ultra Deep Field image has taught us nothing else, it is that every piece of the sky, regardless of how diminutive it may be in the two-dimensional view of the universe through our eyes, holds a wealth of astronomical treasures.  We begin the 2010 Constellation presentations with one such small, but by no means insignificant, piece of the sky.  Canes Venatici (“Now that’s Italian(-sounding)!”) is a young constellation, one of the many additions formalized by Johannes Hevelius in the 17th century and the result of some rather troublesome bookkeeping over the course of written history.  As the story goes, several of the stars within the modern borders of Canes Venatici were originally part of Bootes‘ staff (or club.  Some herdsmen take the protection aspect of their job very seriously).  A poor translation of Ptolemy‘s Almagest from Greek to Arabic to Latin resulted in the “hook” of the staff being turned into “dogs” (accordingly to the translation history provided at wikipedia, the translation went from “the spearshaft having a hook” in Arabic to “spearshaft having dogs” in Latin.  Perhaps the Arabic-to-Latin translation occurred on a late Friday afternoon before a much-anticipated Public Viewing session?). Befitting a new constellation of hunting dogs now accompanying Bootes in his nighttime watch, Hevelius, er, ran with it and gave the mythological canines Chara and Asterion a small but astronomically busy place next to their master.

The two dogs Chara (represented by the star “Chara”) and Asterion (represented by “Cor Caroli”) are identified by only their two brightest stars, which are themselves joined by a short leash in the modern line representation.  The many dimmer stars in this constellation that jump out even with low-power binoculars add multiple “spots” to the imagined bodies of these two dogs.  As they rush ahead of their master Bootes, they point straight towards the hindmost of Ursa Major (or appear to be running past the Big Dipper).  If celestial real estate is any measure of actual size in the ancient illustrations, the giant Ursa Major is right in aligning his gaze away from the two diminutive playful pups.  I’m sure there’s some imagined connection between Canes Venatici and its final bordering constellation Coma Berenices, but I was once told that the explanation can get a little hairy (if you did not recognize that as a poor pun, do read the wikipedia entry for Coma Berenices, which may find its way to a feature in upcoming newsletters).

If we let lying dogs rest for a moment, we find Chara and Asterion in possession of five Messier Objects, including a phenomenal telescope sight that is otherwise most often found by chasing Ursa Major’s tail.  The distance between M3 and M106 marks the total width of this constellation.  M3 (below) is an 8 billion-year-old globular cluster composed of 500,000 stars that rests roughly 1/3 the width of our galaxy from us (33,900 light years).

M3, from Robert J. Vanderbei.

M106 (below, from NASA/CXC/University of Maryland) is one of those distant (well, 25 million light years) galaxies that NASA astronomers have a field day with as they overlay various wavelengths to make visually stunning images.  The strong X-ray lines in its spectrum indicate that a supermassive black hole resides in this galaxy that is in the process of devouring large swaths of stellar and gaseous matter.

M106, from NASA/CXC/University of Maryland.

M94 (below), also known as the Cat’s Eye Galaxy, is a remarkable structure, as it contains two distinct spiral regions in one galaxy (providing the bright central pupil and the darker edges of the eye).  Speaking of two significant features in one, its discovery is attributed to Pierre Mechain and its cataloging by Charles Messier, occurring just two days later (pairs come in three’s?).  M94 is itself the most prominent member of the so-called M94 Group of Galaxies, a closely associated group of (up-to 24) galaxies within the much larger Virgo Supercluster.  Fourteen of these galaxies lie between 9.0 (M94) and 14.2 magnitude, making the search possible with available gear but only under most ideal viewing conditions.

M94, from Spitzer, GALEX and R. Jay GaBany.

The Sunflower Galaxy (M63, below) was one of the first galaxies to have a distinctive spiral quality associated with it (this by Lord Rosse in the mid-19th century).  The short and tightly spiraled arms pack considerable spectral density into a seemingly small space, providing the stem-free sunflower view that, as it contains tens of thousands of suns, might better be called The Galaxyflower.  M63 is a member of the M51 Group, another cluster of galaxies within the Virgo Supercluster that feature, as their crown jewel…

M63, from NASA and WikiSky.

The Whirlpool Galaxy (M51, below) is, perhaps, the third best view of any galaxy to be found at Darling Hill (the second-best being the Andromeda Galaxy (M31) and the first being, you guessed it, our own Milky Way).  We view the Pinwheel Galaxy looking straight down the rotation axis of the pinwheel, providing us with what can be a very clear view of the spiral structure of the galaxy through our scopes (and providing those with big scopes a very clear view of this structure).  I suspect not a single member with a non-GOTO scope has ever said “It’s over in Canes Venatici.”  Instead, I suspect the standard manner of location involves some instruction stating “Look at the last star in the handle of the Big Dipper and go at a right angle about half the distance of the last two stars in the handle.”  If you can see the famous pair Alcor and Mizar in the Big Dipper, you’re almost at M51 in a pair of binoculars.  The bright bulge at the end of one spiral arm is a true companion galaxy.  Computer models indicate that the distortions of the M51 arm at this companion position are a result of the companion galaxy passing through the plane of the M51 some 550 million years ago, as if M51 were in the process of throwing its companion out into the void to be retrieved by our two dogs.

M51, from NASA and ESA.

Lord Rosse, who also identified the spiral structure in M63, observed and sketched the clear spiral structure of M51 in 1845 (shown below).  The sketch he made reminds me of the center swirl within Vincent Van Gogh’s “Starry Night” (shown below).  And speaking of fine art, the Hubble image of M51 (provided as a massive download here) is one of those views that might well make the final cut in the first intergalactic exhibition.

The proverbial “Cat’s Meow” of nighttime viewing from a small pair of stars that mark a small pair of dogs that were spared from the celestial kennel thanks to a mistranslated description of a cudgel.

Clear skies, Damian

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