Constellation Profile - Octans

We continue our journey through the Lacaille constellations of the southern hemisphere with Octans.  This constellation certainly can not be seen from Calgary since it constitutes the South Celestial Pole much like Ursa Minor constitutes the North Celestial Pole.  If you are vacationing south of Canada below 15°N (Guatemala and South) you can glimpse some of the stars of Octans.  To find it all you have to do is look South in the sky.  If you live in Antarctica, look right over your head.

Although not significant for most people in the northern hemisphere it is critically important to those in the south.  We have Polaris as the 'North Star' which you can always use to determine where North is.  In the South, they must use Octans as a reference.  The nearest bright star to the South Celestial Pole is Sigma Octantis which sits a little over a degree away (70').  As a comparison, Polaris sits about 40' away from the pole.  Sigma Octantis is a magnitude 5.47 and thus more difficult to see than Polaris (1.97).  A map of the constellation is shown below.

Octans Map

Octans is the representation of the 18th century invention of the Octant.  An octant was a navigational device used by sailors to measure the altitude of celestial objects from the horizon.  It typically had a scale that went to 90° or just beyond.  When it became clear that the distance between two celestial objects was required, the scale had to extend beyond 90°.  This was provided by the successor to the Octant: the Sextant.  It was represented on Lacaille's planisphere below.

Lacaille Octans

Improving on the diagram several decades later, Johann Bode illustrated the following in the Uranographia.

Uranographia Octans

Octans is not really famous for its deep sky objects.  Melotte 227 is an open cluster of magnitude 5.30 that sits about halfway between Beta Octantis and Phi Octantis.  There are a few dim galaxies from the New General Catalog (NGC) that I have seen the odd astrophotographer nab throughout the years but it is not common.

My polar scope has Octans inscribed on it to polar align your telescope if you are observing or photographer far down in the south.  It looks something like the below diagram.

Polar Scope Reticle

Fortunately, I live in the North and it is fairly easy to line up Polaris for basic polar alignment.

Even though I will likely never have the opportunity to see this constellation, I have created a scale diagram of it below.  Highlighted is the brightest star (Nu Octantis) and the 'Pole Star' (Sigma Octantis).  The yellow cross indicates where the South Celestial Pole resides.

Octans

Interestingly, Alpha Octantis is the 7th brightest star in the constellation.  I have yet to determine how the Bayer letters were applied in this way.

If you are ever close to the equator or below, be sure to check out this constellation.  I know a few of my readers live in Australia and I hope to hear some Octans stories from them!