The Southern Cross

 

When I read the news in early 2023 that David Crosby had passed away, I was saddened and told myself that the next time I listened to CSN's "Southern Cross," I'd have to be reminded that Crosby is no longer with us. 

Strange. Although "Crosby, Stills, & Nash" is like a household word to me, I had to admit on that January day in 2023, that the only song I could immediately think of by them was "Southern Cross." Didn't they have tons of hits? Hmmm. Well, more than the few that I could come up with, anyway. 

Even stranger, however, is that when the news of Crosby's death led me to visit the Wikipedia page for "Southern Cross," it was then that I learned for the first time that Crosby wasn't present in the studio when the song was recorded! His voice is not heard in the song! He had parted ways with the band and was just coming back in the middle of the making of "Daylight Again." His picture on the iconic cover of the hit single from Atlantic Records (above) is misleading!

But what a picture it is! How I would love to get "out of town on a boat [to the] Southern islands" and see the Southern Cross for the first time! Alas! It's an item that I likely will never check off my bucket list.

As an amateur astronomer in the early 1980's, I had known about the Southern Cross only a year or so before the song was released. Even then, still a teenager, I doubted I'd ever get a chance to see it with my own eyes. To this day, the famous constellation remains elusive to me, for the most part.

For the most part??!!!

Yeah, that is, I live far enough south in Arizona, that I have seen the top-most star of Crux (the IAU's official name for the Southern Cross constellation), known as Gacrux, or Gamma Crucis. Back in 2009, while driving at night along SR-83, north of Sonoita, AZ, I pulled off the road to get a picture of the stars on the southern horizon. When I got home, I compared my pictures with a star chart and was able to determine which of those stars was the top of the Southern Cross (see below).

γ Crucis (lower right) on April 1, 2009; bright
glow at lower left-center is Sonoita, AZ

Although Gacrux is magnitude 1.6 (brighter than Polaris, the North Star), being only 1 degree above the horizon, it didn't exactly dazzle me! It was rather anonymous to my unaided eye and only identified later in the pictures I took, so I can't even say that I recognized it when I saw it "for the first time"! And I must admit that on the night I took this picture, it was the last time I saw it. That location along SR-83 is pretty far from where I live now, and there's no good reason to go all the way down there to take another picture. Besides, Border Patrol agents are much more aggressive these days, and they don't like it when you pull off the road down there in the middle of the night. It's only about 25 miles from the border of Mexico.

If you look closely at my image, you'll see another southern-sky object: globular star cluster Omega (ω) Centauri. That's another famous object amongst amateur astronomers. But like Gacrux, it's considered too far south to view from most of the United States. Where I live now in Arizona, Omega Centauri is high enough to shoot from my back yard. But in Pennsylvania, where I got my start in amateur astronomy, Omega Centauri was only visible in places that had an unobstructed view of the southern horizon, and its maximum altitude was only about one degree above the horizon, at best. 

Omega Centauri from latitude 40° 17' N, in 1987

In the photo (above) that I took in Pennsylvania, you can see the blur of trees on the horizon at the bottom of the frame. I was shooting with a 200 mm camera lens on Kodak 1000-speed film. This was a 10-minute exposure at f/4.5. The camera and lens were piggy-backed onto my Meade SCT, which I used for guiding the exposure.

I knew that when I moved to Arizona, I'd be able to see Omega Centauri much better, since it would be higher in the sky. But what I failed to realize was that Arizona isn't really far enough south for Omega Centauri. After all, I had only moved south from Pennsylvania by around 8 degrees of latitude. So instead of 1 degree above the horizon, Omega Centauri is nearly 10 degrees above the horizon in my back yard. That's better, but not great!

Similarly, Gacrux, which was never visible above the southern horizon in Pennsylvania, is only 1 degree above the horizon in Arizona, and only if I drive about 75 miles south of my back yard! So, Arizona lets me see Gacrux, but just barely. Which raises an interesting question: "How far south do I need to travel to see the whole Southern Cross?"

Technically, Crux is only 6° from top to bottom. So, if I were to go 7° of latitude south, I should be able see the entire Southern Cross, with Alpha Crucis (the bottom star) one degree above the horizon. This wouldn't be ideal, but at least I could say that I "saw the Southern Cross." Parts of southern Texas or Florida would provide such a vantage point.

Recently, my son and daughter took a trip to Honolulu. I pestered them to try and see the Southern Cross while they were there. The timing was perfect. The Southern Cross culminates (reaches its highest point above the horizon) at around 9:30 PM, local time in Hawaii, this time of year. Surprisingly, Hawaii isn't all that far south, either! Despite my initial optimism regarding their chances of seeing the Southern Cross, it turns out that from Honolulu, Crux is only about 10 degrees above the horizon. Not bad, but when considering the light pollution of Honolulu, as well as a nearly full moon, the stars of the Southern Cross, being only 10 degrees above the southern horizon, were challenging, at best. They saw Crux better in their iPhone pictures than they did with their eyes.

My daughter's picture of Crux
from Honolulu, Hawaii

To make matters worse, the nights in Honolulu were often cloudy. It took several days before my kids got a clear night to make their first attempt at seeing the Southern Cross. The bright sky and clouds made it difficult, but my daughter succeeded with this picture. I was thrilled to see it! Maybe this is as close as I'll ever get to see the Southern Cross.

I'm sure that sailing "the downhill run to Papeete" (17° latitude) on a clear, moonless night would make the Southern Cross a spectacle worth writing a song about, but even this washed-out, second-hand view through my daughter's camera made me feel like I was seeing the Southern Cross for the first time!

Update:

From her hotel room window, my daughter took the picture below a few nights later. Besides Crux, she captured α Centauri (or, Alpha Centauri), the closest naked-eye star to our sun, at approximately 4 light years away. The actual closest star to our sun is Proxima Centauri (part of the Alpha Centauri star system), which is too faint to pick up with an iPhone through a hotel window! Interestingly, while β Centauri (or, Beta Centauri) is nearly as bright as Alpha, one cannot assume that it is nearly as close to us as Alpha. In fact, Beta Centauri is more than 300 light years further away from us than Alpha Centauri! Neither Alpha nor Beta Centauri can be seen from Arizona. They're both just a few degrees below the horizon at culmination. My daughter's updated picture below does, however, include Omega Centauri, the globular cluster I mentioned above. For comparison, Omega Centauri is about 17,000 light years away! We can see it with our unaided eyes because it's a cluster of possibly 10 million stars, packed into a relatively small area of space measuring 150 light years across. I added some lines and star designations to make it easier to compare her view to what I captured from Arizona.