The Southern Cross is one of the 88 official constellations. Formal name Crux. Like the Big Dipper (which is not one of the official 88), it can be used as a direction finder. Unfortunately, there’s a bit of guesswork involved, since the southern analogue to Polaris is a star too faint to be seen (Sigma Octantis).
Using the Cross to find due south:
Extend the Cross' vertical arm "downward" (i.e. in the direction of the longest piece) by about 4.5 times its length. That point is the South Celestial Pole; whatever ground or water is beneath it is due south. (You want to extend the cross' bottom stick until it’s at a latitude just between Alpha and Beta Centauri, which you’ll find right near the cross.)
A weirder, less useful trick is...
Using the Cross to tell time:
  1. Pretend the Cross is the hour hand of a 24-hour clock. Midnight is at the top of the clock, with the cross basically right-side up, and noon would be at the bottom, with the clock upside-down.
  2. Determine what "time" the cross is telling you.
  3. Add 2 hours for every month that’s between now and April 1. For example, on Aug. 15, there are 7.5 months until April 1, so you’d add 15 hours.
The Cross actually looks more like a kite, because its four main stars describe only the very tips, and your brain tends to fill in that shape. What makes it easy to spot is that its three brightest stars rank among the 30 brightest anywhere in the sky. Also, the Centaurus constellation practically wraps around the cross.

One possible problem that Gritchka's reminded me of: If visibility is clear enough, you'll be able to find a similar diamond-shaped formation in the sky. It's called the False Cross and is part of the quasi-constellation Argo, The Ship (modern astronomers broke Argo up into several smaller constellations: Carina, Vela, 'couple others).

Alpha Crucis, also called Acrux, is at the foot of the cross and is a double blue star. Beta Crucis (also called Mimosa) and Delta Crucis also are blue stars; Gamma Crucis is red.

The Southern Cross isn't as distinctive as the Big Dipper, nor is it as spectacular for most observers, or so I’ve heard.

-- Southern Skies:
-- H.A. Rey’s wonderful book, The Stars, paraphrased from memory (i.e. unreliably).
-- Compton’s encyclopedia:

Side note: The Stephen Stills song is great for beginner guitarists. The chords are just A/G/D, in different permutations, with the occasional B minor, which you can ignore if you really need to.

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