The Southern Cross

Having spent much of my life hiking and camping in the Northern Hemisphere, the Big and Little Dippers and the North Star itself have always been reassuring friends in the night sky. Although I can’t always remember the names of many of the other constellations, their familiar patterns and twinkles far out there somewhere have always provided comfort while way out in the middle of nowhere or even when going outside at night to take out the trash. And winter has always been heralded by the constellation Orion rising late at night and then earlier and earlier as winter progresses until it finally disappears as spring approaches.

But here in New Zealand, everything is different. It is as if some crazy hand of God has mixed and stirred everything up in the night sky and few of the stars form their familiar patterns or are where they are supposed to be, or at least at the right times.

Standing on the beach and looking to the north, I see nothing friendly or recognizable. I might as well be on an alien planet. If lost at night, I am not sure which way I should go.

Down here one of the beacons in the night sky is the constellation called the Southern Cross also known as the Crux, which of course interestingly enough means ‘cross’.

To find the Southern Cross in the night sky, first face south. Well, if I knew which way was south, I wouldn’t need to find the Southern Cross, would I? Well, as a beginner you might be fooled by lots of other ‘false’ Southern Crosses out there so at least for starters face south. Look for two bright pointer stars, Alpha and Beta Centauri. You probably remember that Alpha Centauri is also the closest star to the Sun, a mere 4.37 light years away.

Follow these pointer stars up or across to a four or five star (one star might be faint) constellation that looks like a cross or maybe more like a kite. If you are used to looking at the giant Big Dipper, the Southern Cross is considerably smaller being only about the length of the two pointer stars in the cup of the Big Dipper.

Two bright pointer stars (bottom left) point to the Southern Cross (upper right) (1)

Two bright pointer stars (bottom left) point to the Southern Cross (upper right) (1)

In the Northern Hemisphere, when you find the North Star you are conveniently looking due north. But things aren’t as easy here in the Southern Hemisphere, when you find the Southern Cross, you are kind of looking south but you still have more work to do.

The cross and the pointer stars rotate (actually the earth rotates) around a point termed the Southern Celestial Pole (SCP).

To find the SCP using the Southern Cross, draw an imaginary line connecting the two pointer stars, then another imaginary line in the center of that line and at a right angle to it down towards the horizon. Now while keeping those imaginary lines in place (don’t move them!), draw a line connecting the uppermost star of the cross with the lowermost star in the cross and extend that line down towards the horizon. Where this line intersects the right angle line from the pointer stars is the South Celestrial Pole (SCP). Draw yet another line directly down from this point toward the horizon and you are pointing directly south.

Or an easier way is to just connect the upper and lowermost stars in the cross and measure 4.5 times that length downward on that line and you will be pointing to the SCP.

(1)

(2)

The angle that the South Celestial Pole is above the horizon is your latitude. If you were standing at the South Pole, the South Celestial Pole would be directly overhead. If at the equator, it would be at the horizon. Here in Tauranga, it is 38 degrees above the horizon and hence, the latitude here is 38 degrees South.

For what it is worth, the exact latitude of Tauranga is 37.68 degrees South, that is, below the equator, while the latitude of Colorado Springs where we came from was 38.86 degrees North.

If you go back and look more closely at the photo of the Southern Cross, you will also see a dark black area directly below the cross itself. This is what is called the Coalsack Dark Nebula or simply the Coalsack, the most prominent dark nebula (an interstellular cloud of dust and gases) in the night sky located approximately 600 light years away.

Of course, if you are reading this in the United States, none of this will work because you can’t see any of this from where you are. Sorry. Actually at one time, 5000 years ago, you could see the Southern Cross from the US but because of precession, the oscillating motion of the earth’s axis, it can now only be seen to the south.

The Maori name for the Southern Cross is Te Punga meaning “the anchor” referring to it as the anchor of the great canoe which is the Milky Way, and the Pointers are the anchor’s rope.

As an aside, the New Zealand flag displays the Union Jack in the upper left corner and the rest of the flag contains a blue background signifying the blue sky and sea surrounding the country with the four stars of the Southern Cross.

New Zealand flag

New Zealand flag

The Australian flag looks similar but by contrast contains six stars, a five-star more detailed version of the Southern Cross and a single white Commonwealth or Federation star beneath the Union Jack signifying the unity of the states and territories of Australia.

Australia flag

Australia flag

As time goes on, I am slowly becoming better at picking the Southern Cross out of the jumble of stars here in the night sky. So for now here in the Southern Hemisphere, I guess the Southern Cross will become my guiding light.

 

(1) http://www.google.co.nz/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=RqSkSzlWPgTkvM&tbnid=cmoN2md0pUm8jM:&ved=0CAQQjB0&url=http%3A%2F%2Fwww.sydneyobservatory.com.au%2F2012%2Femilys-eventful-internship-at-sydney-observatory%2F&ei=dbWiU97lBJL-8QW4toKQBg&bvm=bv.69411363,d.c2E&psig=AFQjCNH2zsHQuCEPgZe_9pRt3cP97oTPPA&ust=1403258411497590

(2) http://www.sydneyobservatory.com.au/2008/finding-south-using-the-southern-cross-an-essential-skill/Finding south using the Southern Cross, drawing Nick Lomb

Advertisements

One thought on “The Southern Cross

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s