Adventures from Back of Beyond

Sunday, June 17, 2007

Southern Cross Redux

Although the Garden Island of Kauai is the northernmost of the main Hawaiian Islands, it's still within the tropics, at roughly 22 degrees north latitude, and well south of the rest of the U.S. So Hawaii, including Kauai, is the only state from which Crux, the Southern Cross, is visible.

I learned this recently on a two week visit there. We stayed right at the southern tip of the island, near Makahuena Point, well positioned to overlook literally hundreds of miles of empty, dark, open ocean at night.

On our previous visit to the islands, we finally discerned the Southern Cross hanging low over the southern tip of the Big Island (see Southern Cross) during a spectacular night time hike out to the flowing lava.

This visit, because we were situated ocean front on the southern tip of Kauai, we could see the Southern Cross almost every night just by looking out our lanai.

Sure, there were almost constant low clouds moving in and out that would block the stars every now and then. That's just the nature of the trade winds and all that humidity (almost a constant 70% plus) out in the middle of the Pacific Ocean. But there was also ample opportunity for some serious star study. That's where our notebook computers came in handy.

We had 3 of them with us, which seemed like overkill, plus wireless high speed internet. That made it easy to take a notebook out on the lanai, or outside under the stars, turn down the monitor to very low light, and search the internet for details on what we were seeing. Here's what we found out.

First, I was somewhat thrown off my usual orientation, because Scorpio stood so high in the sky it was almost overhead. From the rest of the U.S., it typically sits in the lower southern portion of the sky. That relatively high position for the big scorpion makes it possible to see all the stuff below, or south, that we can't normally see in the U.S. -- including Crux.

The Southern Cross by itself doesn't directly indicate the celestial south pole. There is no corollary to Polaris in the southern sky that provides an accurate and true south. What the Southern Cross does is point you in the right direction. To locate true south, you also need to identify Centaurus, the big half-man half-horse in the southern sky.

In the rest of the U.S. you can barely make out the top of Centaurus in the southerly latitudes with good light conditions (meaning dark skies). It's probably not visible at all in the more northerly states.

But if you're in Hawaii, wow. There sits the entire Centaur in full bright view, which is important. Along the Centaur's lower side are its two brightest stars, Alpha Centauri and Beta Centauri. Those two comprise the pointers, which together with the orientation provided by the Southern Cross, triangulates to a specific point in the sky which is directly over the celestial south polar axis. Centuries ago, that's how seafaring mariners would navigate in the southerly latitudes.

Morever, Centaurus is significant because of Alpha Centauri, the third brightest star in the sky (behind Sirius and Canopus, and just ahead of Arcturus). Alpha Centauri is fairly well known as the closest star to the earth, but actually it's a system of at least 3 stars gravitationally bound, one of which includes Proxima Centauri, considered the closest star to the earth. Proxima is only a mere 4.2 light years, or roughly 25 trillion miles away, a stone's throw in the universe.

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