'Crux', The Southern Cross.

The southern cross is the best known constelation in the southern hemisphere.

However, unlike the navigator in the northern hemisphere, the southerner has no fixed star conveniently placed to mark the South Celestial pole.

Quite the opposite, there is in fact an inky-black dark patch across that area of sky.

This dark patch looking like a hole in the firmament is actually a cloud of gas obscuring any stars beyond, which has been appropriately called the ‘Coal Sack’.

To find out where in this ‘coal sack’ the south celestial pole lies, there are, fortunately several ‘pointers’, the most famous of which is the Southern Cross.

Southern Cross

The Southern Cross, the constellation ‘Crux‘, is in one of the brightest portions of the southern Milky Way.

It is also one of the smallest constellations.

Fortunately three of its stars Acrux, Mimosa and Gacrux are among the brightest objects in the night sky.

Counter clockwise next to Crux are another pair of bright stars Alpha and Beta Centauri which are known as the ‘Southern Pointers’.

An imaginary straight line drawn clockwise across the pointers will point towards the head of the cross.

It’s important to identify the cross using the pointers as there are several other cross like groups of stars, including the one known as the ‘false cross’.

Once the cross has been correctly identified, if we draw an imaginary line through it’s head and carry it on through the bottom, somewhere along this line, where it crosses the ‘coal sack’ is the South Celestial Pole.

If we then draw a perpendicular line from that imaginary line running between 'Pointer Stars' and extend this into the ‘coal sack’, where it crosses the line from the cross is the position of the South Celestial Pole.

If this perpendicular line from the pointers were extended beyond the celestial pole it would point to Achernar a very bright star an equal distance beyond the pole.

Another position line can be drawn from the ‘Southern Triangle’.

A line from the apex of this star group cutting the base at right angles, then extended, will also cross the position of the South Celestial Pole.

Terrestrial south is of course directly below the south celestial pole.

So while the navigator in the south does not have a conveniently placed pole star there are plenty of pointers to indicate the direction of south.

You might like these

  • Weather Sayings

    Weather sayings, worth remembering, sailors use phrases, expressions and idioms for short term forecasting, many have scientific explanations.

  • Maritime Weather Patterns

    Global weather patterns influence your local marine conditions, understanding how these work will help you to interpret forecasts, help to keep you safe and your boating enjoyable.

  • Tides, how they are caused and predicted.

    Tides, tidal streams, sea level predictions and marine currents and what the leisure boater should know about Tide tables, charts coastal height prediction data.

Recent Articles

  1. Keels to Wheels on display at Burrard Yacht Club (PHOTOS)

    Keels to Wheels on display at Burrard Yacht Club, photo by Paul McGrath


    Keels to wheels were on display at the annual Burrard Yacht Club's Classic Boat and Car Show held at the club's North Vancouver base on Saturday June 8th.

    See more by Paul McGrath at North Shore News

    Read More

  2. Wood and Glory

    (Bob Meninna for the Record Bee) Over 150 attended the Wood and Glory XXI Antique and Classic boat show at Konocti Vista Casino and Resort


    Over 150 attended the Wood and Glory XXI Antique and Classic boat show at Konocti Vista Casino and Resort over the weekend.

    Read more by Bob Meninna at the Record Bee

    Read More

  3. Flat-Packed Howth Yacht Club Classic Wins Podium Place

    Rosemary heads seaward for the annual challenge of the Lambay Race, her maiden sail in her restored form


    When photos circulated of the mangled remains of the 1907-built Howth 17 Rosemary in the wreckage of her storage shed on Howth’s East Pier after Storm Emma in March 2018, many unacquainted with the sp…

    Read More

 

Comment Form is loading comments...