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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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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The art of walking country, a response

This article, a curatorial response to the 2012 exhibition, was written and considered for the prestigious national magazine Art Monthly. It was not used.

Cecil Hackett - At the summit of Mt Woodroffe, June 1933 (c) Wakefield Press

Cecil Hackett – At the summit of Mt Woodroffe, June 1933 (c) Wakefield Press

When I saw the cover image of Philip Jones’s Images of the interior: seven Central Australian photographers (Wakefield Press 2011), I knew that I needed it for the hybrid art–recreation exhibition I was curating: walking country: 30 years in the arid rangelands, a photographic journey.

Download the full article The art of walking country

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Hot weather walking, drink lots of water

With an October heat wave and temperatures soaring into the high-30s and 40s, it is a timely reminder to make sure before you leave the carpark that everyone has at least 3 litres of water, and that you plan to finish the walk before midday.

Also, as leader, you should take the satellite phone and/or PLB with you in case of emergency.

Why we walk early and recommend to drink 3+ litres on summer bushwalks

In hot weather, we maintain a safe body temperature by evaporating sweat from bare skin. On really hot days, water loss from the body by sweating may reach 1.5 litres / hour.

The table below indicates the minimum water intake to maintain body fluid while at rest in the shade. There is generally little shade where we walk, and temperatures in the sun can be 10-15°C higher than that in the shade. Walking may double the stated water requirement.

Mean temperature 20°C 25°C 30°C 35°C
Water required, litres 1.2 L 1.4 L 2.5 L 5.1 L

Our normal (internal) body temperature is 37.2°C. A slight increase in body temperature is not unusual for people bushwalking under a hot sun. A body temperature of 38-39°C can be tolerated, but higher temperatures can lead to serious injury and death.

When the air temperature rises above skin temperature, heat loss can only be achieved by sweating.

 

Ongoing hydration: before, during & after the bushwalk

Begin hydration the night before the walk, and drink 0.5-1 litre of water in the morning before starting the walk. You will then be well hydrated at the start of the walk.

On the walk, it is better to drink small volumes regularly and often (250-350 mL every 20 minutes) to maintain fluid levels rather than drink a larger volume every hour.

Have additional cool water in the car to drink at the end of the walk, and keep drinking regularly for the rest of the day until your urine is clear.

 

Hyperthermia (heat illnesses)

Heat-related illnesses range from cramps to heat exhaustion and the life-threatening heat stroke.

Heat cramps are (often painful) muscle spasms caused by exercise and heavy sweating.

Treatment: Cramps can be relieved by rest in the shade, gentle massage, and taking oral fluids containing sodium (such as common salt, or gastrolyte).

Heat exhaustion is caused by a loss of salt and water from the body, usually by heavy sweating. Symptoms include headache, dizziness, nausea, chills and drowsiness. The skin may be warm or cool, with sweating. If left untreated, heat exhaustion can lead to heat stroke.

Treatment: The focus is on cooling and rehydration. The person should cease all activity and rest in the shade. Cool the skin by wetting and fanning. Give the person cool, lightly salted water (or electrolyte replacement). Fluid replacement of 1-2 litres over 2-4 hours is recommended. The person should rest over the next 24 hours, and not resume the activity until fully recovered.

If one person is suffering, then consider how others in the group are feeling as well.

If heat exhaustion is untreated, heat stroke may develop.

Heat stroke is a medical emergency with a mortality rate of 80% if not promptly and effectively treated. In this state, the body systems loses its ability to regulate body temperature (so sweating stops) resulting in an elevated core temperature. The organs literally ‘cook’ in our ‘body oven’. Signs and symptoms for heat exhaustion may be present, as well as a hot, red and dry skin, rapid pulse and breathing, and especially altered moods (irritability, confusion) and poor coordination.

Treatment: Immediate rapid cooling. Rest in shade, loosen and remove excess clothing, sprinkle with tepid water and fan aggressively, regularly towel dry skin, apply cold packs where blood vessels are close to the skin (neck, armpit, groin). Most patients with heat stroke are initially unconscious or semi-conscious and should not be given oral fluids.

Organise evacuation immediately.

 

Information sourced from Bushwalking and Ski Touring Leadership (2000) published by Bushwalking and Mountaincraft Training Advisory Board Inc.

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30 years walking the bush

To celebrate 30 years of of bushwalking club, be part of these unique events:

walking country: a photographic journey opening 6pm September 21 at Olive Pink Botanic Garden. The exhibition, proudly sponsored by the Northern Territory Government, features archival and rarely seen photographs of stunning places most people will never get to visit. In photo, audio, art and story, the rugged beauty of the Centre will be on show until October 8.
Visit the WALKING COUNTRY webpage for more information.

bbq | camp | walk at 2 Mile : a weekend camp and selection of walks of various standards from 2 Mile on the Finke River.
BYO meat & grog & stories.
All welcome.
camp Saturday 22 September | walks Sunday 23 September

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