Exploring the Southern Constellations
September 2008 :
In the summer of 1865, noted American newspaperman and politician Horace Greeley penned, in an editorial, an admonishment to young civil servants in Washington DC. Greeley urged those who complained of low pay grades in the Capitol area to “Go west, young man!”. This maxim applies, in an astronomical sense, to me, except for the word “west” - I’d substitute west with south, as in “Look south, stargazers!”. Throughout my years in astronomy I’ve been intrigued by constellations, stars, and deep-sky objects that only just rise above our southern horizon from my local latitude of about 42 degrees north. Even more alluring are those southerly sky objects, so mythical in our imaginations, that lie concealed beneath the horizon owing to their declinations of greater than -48 degrees, which is the unfortunate southern limit for viewing in these parts–we simply can’t ever see anything further south in the sky than declination -48, from latitude 42 degrees north, that is.
However, even -48 declination is, in nearly all cases, impossible to achieve because everything’s got to be perfect to permit seeing right down to what I term the “theoretic horizon.” You can’t have any trees, buildings, hilly terrain, etc. which would block your view south. Nor can there be any haze, fog, or clouds at the horizon, not to mention nuisance skyglow from heavy light pollution, or a bright Moon in the sky. Sounds like a fantasy, right? Well, my good friend Tim Dube, a veteran amateur from Douglas, MA, got me interested in Wallum Lake several years ago. The lake lies half in Rhode Island and half in Massachusetts, and the northern terminus has a handy public boat ramp adjoining it with a generous cleared area surrounding, with no lights save for a few at homes a fair distance away along the east shore. Even these are screened by trees and brush and present no problem when we’re viewing due south from the boat ramp, which is part of a Massachusetts State Park. Wallum Lake’s longer axis is oriented due north-to-south, meaning that views to the south are over a considerable distance of open water with bearable skyglow beyond the southern shore. Add-in a “lucky” sky to this equation and the fact that atmospheric refraction tends to “lift” sky objects a bit higher above the horizon than they might actually be and you’ve got the magical ability to see right down to my theoretical horizon, which can actually become the true horizon!
I suppose many of us tend to want most what we know we can’t have–it’s human nature after all. This explains my interest in low-lying stars that are tough to see most of the time, as well as all those splendid objects further south that will only become visible here after many thousands of years hence, when Earth’s axial precession will reveal the Southern Cross to mid-latitude Northern Hemisphere observers. (Assuming, of course, that distant descendants of ours will be around!) I’ll write a piece on observing from the Big Cypress Swamp Preserve (adjacent to the far northwestern corner of the Everglades) in southern Florida in a future issue, but for now, let me tell a little anecdote about just one experience at Wallum Lake. Gamma Velorum is a favorite star of mine, one I’ve seen many times from Florida. A few years back I figured I’d try to spot it from this latitude, in March. I checked its coordinates and consulted a sidereal time chart so as to calculate a transit (culmination) time, critical for having any hope of glimpsing anything so very, very low above the horizon. Gamma Velorum is a possible multiple system; the primary itself is a spectroscopic binary and the brighter of these suns is the brightest Wolf-Rayet class star known–the combined apparent magnitude of this tight binary is 1.8 variable, making it about the 33rd brightest star in the entire sky. Declination of the primary is -47° 20’ 12”, but there’s an unrelated visual companion of magnitude 4.3 even further south by 32”, separated by 41” from the primary. Remember, -48 degrees declination is as far as it is possible to go from latitude 42!
Tim Dube and I set up at the boat ramp on a near-perfect night with no clouds or haze visible at the southern horizon. I started scanning with 10x50mm binoculars a few minutes prior to estimated transit time and there it was–Regor (Gamma’s proper name) glimmered back at me, almost at the horizon over the lake’s southern shore! We put a scope on the star and, using a low-power eyepiece, managed to resolve the magnitude 4.3 companion. I was delighted and thought this event to be significant.
The accompanying special constellation table is something I dreamed up years ago. I was curious about exactly which constellations might technically be visible along the southern horizon throughout the year from our “home” latitude here. A good deal of time and research went into the resulting information. I checked star atlases and consulted several good texts to generate the table. I hope others will appreciate the results.
Of the 88 constellations covering the entire sky, would you believe that only 15 are not ever visible from our latitude? We can see small extreme northern sections of many, but just 15 never rise at all here.
