Johannesburg Centre, Astronomical Society of Southern Africa


Southern Sky Star Hopping

Turn Left at Orion*

This catchy book title grabs my attention every time I read it! My imagination runs wild, with visions of space travel and summer skies. At the moment we see the last of the winter constellations disappearing into the west, with Orion the dominant constellation of the evening sky.

Each year in the astronomical calendar, we are faced with two seasonal contrasts that considerably affect our time at the eyepiece.

In winter we have clear crisp skies with some of the greatest objects and constellations, but we find excuses not to venture out.

In summer, while we enjoy the outdoors and holidays, clear nights are few and far between. We seem to be plagued more by weather systems than afternoon thundershowers nowadays. There must be one astronomical law other than telescope aperture, which has to do with overcast skies or rain when planning a summer star party (just think of the past few ASSA year-end gatherings). This is the time when you want to share the sky with those you could not convince to venture out in winter, only to disappoint them. Summertime is also the seasonal phase when you consider swapping your equipment for a set of golf clubs!

However, there is nothing quite like a warm, clear summer evening when it does present itself. Some of my favourite deep-sky objects nestle in these constellations and I look forward to revisiting them each year.

Orion is up and the great nebula (M42) in the sword can satisfactorily be the focus of an entire viewing evening. It does not matter if you view the Orion nebula with three inches or thirty inches. It is magnificent. With such a captivating object, I often do not venture much further.

If you are not drained from the visual feast of M42 as well as scrutinising the well-placed Saturn and Jupiter, there is a worthwhile star-hop to one of my favourite deep-sky objects.

Turn Right at Orion

NGC 2362 is a gem of an open cluster in Canis Major, surrounding the 4th magnitude Tau Canis Majoris. I first became interested in NGC 2362 after reading the description in "Observing the Constellations" by John Sanford, and saw it for the first time a few years ago through Chris Stewart’s 10 inch Meade during a casual observing evening with a few ASSA members. As with all the wonderful objects up there, one never forgets the first view.

I have been following a recent series of articles in Sky & Telescope along the lines of "My Favourite Deep-Sky Wonders". I compare my own favourite objects to these selections from well-known amateurs, as well as for future targets. I was not surprised to find this open cluster mentioned as being one of James Mullaney’s top ten objects, author of The Finest Deep-Sky Objects. However, his beautiful description does not mention NGC 2362’s most distinguishing feature.

Seeing Triple

The star-hop to NGC 2362 is straight forward, but should include a stop at Beta Monocerotis, making an evening of outstanding multiple stars. Starting at Orion’s belt and moving right towards Sirius in Canis Major, try to identify the two brightest stars in-between these two constellations in an otherwise empty area of the sky. These are Gamma and Beta Monocerotis. Beta is the one closer to Canis Major as well as the horizon.

Beta is one of the best triple stars for small scopes and I have been able to split the star using a converted 80mm telephoto lens. William Herschel first discovered this trio in 1781. He described it as "one of the most beautiful sights in the heavens" (Burnham’s Celestial Handbook – pg 1189).

NGC 2362 lies below what I call the "y" of Canis Major. This constellation has quite a few bright stars, an imaginary line from Sirius splits into a "y" shape.

Envisage a triangle using the two bright stars on the bottom "y" axis as a base. Tau Canis Majoris lies at the apex. When looking through your finder or hunting it down through the eyepiece, you might miss it at first as there are a few bright stars in the area. Keep trying until you find the beautiful sprinkling of stars surrounding the 4th magnitude star.

A six-inch telescope should resolve the small cluster consisting of some 40 to 60 stars. Because of the small compact size and brightness, this object looks even more impressive in larger telescopes. Upon closer inspection and depending on the seeing, you should be able to see that Tau in the centre of this jewel box is itself also a fine triple star!

The discovery of NGC 2362 has also been accredited to William Herschel, but interestingly was first discovered by Hodierna in a catalogue published in 1654 (for more information - www.seds.org). Giovanni Batista Hodierna (1597-1660), astronomer at the court of the Duke of Montechiaro, compiled a catalogue of some 40 objects. Their rediscovery had to wait until the 1980’s. He used a simple Galilean refractor with twenty times magnification.

Inside the boundaries

Canis Major rises high into the sky and will be well placed over the coming months. You could try to hunt down Canis Major’s Twenty-Six Star Clusters (see Astronomy, February 1988 - pg 91). There are also a few brighter galaxies of which NGC 2207 is the most exciting and challenging, as it is an interacting pair which can be detected at high power in larger scopes. The tiny blue planetary nebula IC 2165 (8 arcseconds, magnitude 12.5) is positioned near the border with Monoceros.

Notes

 Object        Type          Const.     R.A.         Dec
Beta Mon      Multiple star    Monoceros     6h28.8m –7º02’
NGC 2362    Open Cluster   Canis Major    7h18.8m -24º57’

Sky & Telescope Articles
My Favourite Deep-Sky Objects – by Jay Reynolds Freeman

S&T October 2001 - Pg 110

My Favourite Deep-Sky Wonders – by David Levy

S&T April 2001 - Pg 113

My 10 Favourite Deep-Sky Wonders – by James Mullaney

S&T December 2000 - Pg 120

My Favourite Deep-Sky Wonders – by Stephen James O’Meara

S&T August 2000 - Pg 105

*Turn Left at Orion
By Guy Consolmagno and Dan M.Davis

Eric Brindeau


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