The Plough & Southern Cross

[jenks]

I'm currently at work down under and last night I saw The Plough and the Southern Cross in the sky at the same time; 20 degrees south, 113 degrees east. I didn't know that The Plough was visible down here, it was 'upside down', with the handle to the right pointing slightly up.

Polaris wasn't visible, it was below the horizon, but by extending an imaginary line down from the pointers (4 times longer than the distance between the pointers) I estimated a northerly direction.

The Southern Cross was almost opposite The Plough (as you'd expect), it was quite bright but not large. It took a few minutes for me to locate due to the thousands of other stars, Milky Way and a cloudy astronomical effect called the Coal Sack. Again I followed an imaginary line from the bottom star to the horizon and estimated a southerly direction. There was a larger 4 pointed constellation to the right, not as clear, so I thought that it was the False Cross, as it was slightly west of south.

 

[TinkyPete]

I've been to kenya and stood at the equator and seen both polaris and the southern cross at the same time was great for naviagting could easily find North and South at any time when I was there.

 

[wicca]

It's interesting to get a sextant angle on Polaris if you've got a nice clear horizon because it will give you a rough idea of your latitude. If for instance you were adrift far out to sea and lost for position, drifting West. If you get an angle of 30 degrees then you're South of Bermuda, if you get 35 degrees then you're North of it. If on the other hand you get somewhere about 32 30 give or take (I know about refraction etc: ) then it's get 'yer Bermuda shorts on and don't eat the cabin boy just yet..

 

[ged]

I'm currently at work down under and last night I saw The Plough and the Southern Cross in the sky at the same time; 20 degrees south, 113 degrees east. I didn't know that The Plough was visible down here, it was 'upside down', with the handle to the right pointing slightly up.

Up here (or anywhere north of 35 degrees north latitude) the plough is circumpolar (never sets). Down there it rises and sets. The Southern Cross can't be seen anywhere north of latitude 35N. There are tips for distinguishing it from the two 'false crosses' in one of the references below.

Polaris wasn't visible, it was below the horizon

Wherever you are on the surface of the Earth you only get about 180 degrees of sky from the horizon, up to zenith, and on down to the horizon opposite. At the North Pole, Polaris is overhead. Move 90 degrees south from there and it's on the horizon (and you're on the equator). So you can't see Polaris very much south of the equator. It's not perfectly at the pole, it's just over two-thirds of a degree off, but it's close enough for this hand-waving stuff and for example steering a boat on the sea.

... by extending an imaginary line down from the pointers (4 times longer than the distance between the pointers) I estimated a northerly direction. ... The Southern Cross was ... quite bright but not large. Again I followed an imaginary line from the bottom star to the horizon and estimated a southerly direction.

If you like this sort of thing and you haven't seen this book, then order it right away:

http://www.starpath.com/catalog/books/1830.htm

If you're disappointed with it I'll buy it from you as I could use a second copy (the cover has fallen off mine) but I know you won't be. I think this book is the single most important work on emergency navigation that has ever been written, and anyone interested in being outdoors and away from civilization should read it.

See also

http://en.wikipedia.org/wiki/Coal_Sack
http://en.wikipedia.org/wiki/Vela_(constellation)
http://homepage.mac.com/kvmagruder/bcp/aster/constellations/Cru.htm
http://homepage.mac.com/kvmagruder/bcp/aster/constellations/Cen.htm