Direction finding by the stars in the southern sub-tropics

by Michael Giacometti

In the southern hemisphere, all of the stars and constellations rotate around the South Celestial Pole (SCP). Unlike the northern hemisphere with its North Star, there is no ‘South Star’ situated at the point of the SCP.

The Southern Cross and Pointers are used to navigate in the temperate and sub-temperate zones of the southern hemisphere. However, they are of less use to navigators in the southern sub-tropics. This is especially true during the southern summer, from October to March, due to the tilt of the earth northward so that the sun shines more directly at the Tropic of Capricorn, and less of the southern night sky is seen.

In the southern sub-tropics the SCP is located close to the horizon. The Southern Cross and Pointers, being situated close to the SCP, are sometimes visible, but for long periods of the night they ‘set’ and drop below the horizon. At Alice Springs (virtually at the Tropic of Capricorn) in the summer months, the Southern Cross does not ‘rise’ (or become visible) until the early hours of the morning. Instead, south can be found using the stars Canopus and Achernar. With the SCP, these two stars roughly form an equilateral triangle.

A practical guide to locating south

Two other constellations can assist in locating Canopus and Achernar: the Belt of Orion, and Sirius (also called the Dog Star).

These four – Orion’s Belt, Sirius, Canopus and Achernar – describe an asymmetric arc in the night sky.

1. Start by locating the Belt of Orion.

2. Sirius, the brightest star in the sky, is in the opposite direction to (and in a straight line through Orion’s Belt from) Pleiades, the Seven Sisters.

3. Canopus is the second brightest star in the night sky. The angle of the arc of Sirius–Canopus from Orion–Sirius is about 135°, and the length of the Sirius–Canopus axis is about 1½ times that of Orion–Sirius.

4. Finally, Achernar is the brightest star in the constellation Eridanus. The angle of the arc of Canopus–Achernar from Sirius–Canopus is about 135°, and the length of the Canopus–Achernar axis is about the same as that of Orion–Sirius.

5. Using the location of Canopus and Achernar, project a third point outside the arc (on the convex side) which would form an equilateral triangle (a triangle where all sides are the same length). This projected point is the South Celestial Pole. (It lies roughly on the extension of the Sirius–Canopus axis). Drop a plumb line from the SCP to the horizon and you have south, accurate to within a few degrees.

[The Southern Cross and Achernar are on opposite sides of the SCP in the night sky. In the southern tropics, if one can be seen, then the other cannot.]

A star chart can help you to locate the constellations (such as those available from http://skymaps.com).

Note: This is an addendum to section 5 of the Map Reading Handbook, edn. 2 (TASMAP 1991).

Download a copy of the instructions [displayed below] here: skymap south by stars PDF

 

Finding South by stars

Star chart for Southern Hemisphere November 2014 from skymaps.com.

Note: the southern hemisphere star chart is designed for use at 35°S (the latitude of Adelaide) and up to 15° either side of this latitude (as far north as Tennant Creek. For the southern tropics, refer to the Equatorial star chart.

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A walk in the East Macs

Nick Tyllis recaps a walk in the East Macs on 2 August 2014

A walk in the East MacsWalk: Goat Camp Creek Gorge
Length: around 12 Km
Grade: Hard – 80% was boulder hopping, 5 % sphincter-challenging waterfall and 15% flat woodland.

All images by Dianne Alford

A group of four curious and intrepid club members went East to explore some stunning gorges and gullies, cut into the rock formations. The area is open woodland with quartzite ridges cut by multiple waterways flowing from the northwest to the southeast into Giles Creek, which drains into the Todd River.

Goat Camp Creek GorgeWe chose to explore an area around a gorge cut by Goat Camp Creek, about 95 Km east of Alice Springs, along the Arltunga road. The weather was cool with minimum of 0o C to a maximum of 17o C and windy – perfect off-track walking conditions.

The track into the property took us to within 1 Km of the Northern entrance into the gorge. The walk up to the gorge was along flat, relatively even, lightly-wooded terrain. There is lots of evidence of horses and cattle, but mainly horses. The gorge itself, is about 2.5 Km long, rocky, with steep walls and numerous shallow pools of sweet water.

We followed a gully eastward, then up a stunning (one of many) waterfall, with a large, dark pool at the bottom. Then we walked down a show-stopper of a waterfall back into Goat Camp Creek Gorge. This time the photographer was too focused on getting down alive and in one piece to take any further pictures.

The walk was an easy day walk, but there is still lots to explore in the area and could easily make for a multi-day walk over a few happy days.

Goat Camp Creek waterfall

Goat Camp Creek Gorge

 

 

 

 

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Walk this weekend

The bush walk for this weekend, Sunday 31 August was mistakenly left off the new program.

31 August – Section 1 of Larapinta Trail. Contact Nannette 0409 377 545 | nannettehelder@bigpond.com

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Leaders Guidelines updated – Driver responsibilities

It may seem like common sense, but all drivers have a duty of care to their passengers. This applies on our bushwalks too. To clarify this, the following has been added to the Leader Guidelines:

Driver Responsibilities

In terms of the potential of major injury or death, driving to and from the walk is probably the riskiest part of bushwalking. Drivers should put the safety of their passengers (their fellow bushwalkers) first. Stop or share the driving if tired or unwell.

Due to post-walk fatigue, drivers should be ‘Sober Bob’ and refrain from alcohol and other drugs.

As a passenger, please inform the driver to slow down or pull over if you feel uncomfortable or unsafe.

You can download the full guidelines here.

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2013 in review

The WordPress.com stats helper monkeys prepared a 2013 annual report for this blog.

Here’s an excerpt:

A New York City subway train holds 1,200 people. This blog was viewed about 6,000 times in 2013. If it were a NYC subway train, it would take about 5 trips to carry that many people.

Click here to see the complete report.

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Updated petrol sharing guide for car pooling

With rising fuel prices, the Petrol Sharing Guide has been updated.

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Walks program up to June 2014 released

The Central Australian Bushwalking club program for walks up to June 2014 is now out. View it on our Bushwalks & Activities page.

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