A Challenge - The gauntlet has been thrown!

This one's for all you astrophotographers out there, because I doubt seriously anyone's going to ever see it through an eyepiece. I'm talking about NGC 6481, an asterism (once thought to be an open cluster) in the constellation Ophiuchus. (The image below was taken from WikiSky.)

As you can see, it's nothing more than a string of 5 unrelated stars, ranging from magnitude 14.25 (at the brightest) to 16.75 (the dimmest). Only a chance alignment along our line of sight connects them. And considering that the faintest thing I've ever managed to positively identify through my largest scope was magnitude 13, this "object" would be futility personified for me to even make the attempt to observe.

But it is nevertheless quite beautiful, and more than worthy of imaging. Here's another, with a bit of context thrown in.

I love how some fainter stars beneath NGC 6481 complete the accidental arrangement, forming an almost perfect square. By the way, I searched the internet in vain for more information about this fascinating object, but in vain. I wasn't able to find anything about the distances of its component stars, or anything else for that matter.

I did find this bit of valuable information, however:

Right Ascension: 17h 52' 48"
Declination: 4° 10' 01"

Happy hunting!

Images

“That day we first

Beheld the summit of Mount Blanc, and grieved

To have a soulless image on the eye

Which had usurped upon a living thought

That never more could be.”

(Wordsworth, The Prelude, Book Sixth, lines 524-528)

Images. So much of amateur astronomy is all about images, whether they be on the observer's retina via an eyepiece, or digital data from photons collected by a camera. Whenever I give a talk to the public, I will almost inevitably toss out the following question to the audience. "Astronomy is the most visual of all the sciences. Why is that?" The answers can be quite interesting, but my own take on the question is that astronomy is the only science where we can't actually touch the subject matter, put it in a laboratory, or run experiments on it. (Note: I do not consider data from space probes within our solar system to be astronomy, but rather planetology.) 

As to the above quotation from Wordsworth. About 10 years ago, I decided I just had to read his Prelude - a daunting task if ever there was one. It was to me mostly forgettable, but this one passage managed to burn itself into my brain. I felt like the poet was speaking directly to me.

Now I've always been a voracious reader, for as long as I can remember. Way back in grade school, the library was one of my favorite places to be. And as soon as I had pocket money, I was forever buying paperback books (mostly science fiction) as fast as I earned any. But from the very beginning, I always hated most illustrations. I wanted my own impressions of what something looked like to prevail, and it's a curious fact that images trump our own imaginations almost every time. I might have built up a picture of what John Carter of Mars ought to look like, but a single cover illustration could pop my mental image like a soap bubble. And the victorious illustration always seemed to be so damned inferior to what I had thought up.

This was especially true for one of my all-time favorite books, The Lord of the Rings. Here my imagination was paramount, and for a long time was unchallenged by anyone else's ideas. (I read the trilogy for the first time in 1968, and have re-read it pretty much annually since then.) The movies came out decades later, and I resolutely avoided even glancing at any pictures from them. If I happened to be in a movie theater when a trailer for one of them came on, I'd shut my eyes until it was over.

Martian landscape, by Chesley Bonestell

So when I read those lines from Wordsworth, I knew that he and I shared this same trait. What we imagined was almost inevitably superior to the dull reality. Take our own Solar System. Who in their right mind would ever choose the actual Mars over Edgar Rice Burroughs' Barsoom? Or the real world Venus over C.S. Lewis' Perelandra? Or any planet, for that matter, over the unparalleled imagination of R. Frank Paul?

No contest, right? And the same goes for the galaxy. Back in the 1960s, when I was reading that mountain of SF novels, it was so easy to picture one's self (or some future version of me) flitting from star to star in my spaceship (which always seemed to resemble a WWII German V-2 rocket bomb), finding a conveniently breathable atmosphere on whatever planet I touched down on, and conversing with untold numbers of intelligent alien species. But now we must sadly admit defeat before the iron universal speed limit of 186,000 miles per second, and the omnipresence of lethal cosmic radiation.

Science ruins everything!

The Tail of the Serpent

One of my favorite spaces of the sky for just random stargazing is Serpens Cauda, or the Tail of the Serpent, along with the neighboring western edge of giant Ophiuchus. Just gliding up and down the length of this, to the naked eye rather unimpressive constellation, one discovers fields of view crammed full of stars, some belonging to open clusters with formal catalog designations, and others simply strung together in anonymous asterisms and star streams - but all of it just plain beautiful.

IC 4756

Start by taking a look at IC 4756, perhaps the jewel of the whole area. First off, this open cluster is HUGE - almost twice the size of the full moon. But in the eyepiece it looks even larger than that, due to its sitting right on top of the Milky Way. So there are stars, stars, stars everywhere - impossible to tell where the cluster ends and the background stars begin.

NGC 6633 (off to the right)

Right next to IC 4756 and just over the border into Ophiuchus is NGC 6633. The two clusters' proximity ro each other is due to chance line of sight alignment. IC 4756 is more than 13,000 light years away from our Solar System, while "neighboring" NGC 6633 is a mere tenth of that distance from us. So it is obvious that it is much the smaller of the two. NGC 6633 occupies an area of the sky roughly equivalent to one full moon. Like its sprawling neighbor, it is nearly impossible to determine just where  the cluster ends, end everything else begins.

From here we stray into the realm of uncataloged asterisms, whirls, knots, and streams of stars, like a turbulent river sliding off to the southeast, ending up in Ophiuchus at Poniatowski's Bull (see my posting to this blog on September 17, 2017). This V-shaped asterism resembles in miniature the Hyades open cluster in Taurus, and contains a number of attractive double stars.

I often spend time with the serpent's tail when I just want to relax and "take it all in" without looking for anything in particular.

At the Birth of Creation - HD 150283

Most amateur astronomers love to boast about the furthest thing they've either seen or imaged in the sky, so how about spending a glance or two taking in the oldest object up there you're likely to ever see? I'm talking about the blue-white subgiant star HD140283 in the constellation Libra. HD140283 is an extremely metal-poor visitor to our neighborhood from the galactic halo (its inclined orbit about the Milky Way's core causes it to pass through the spiral arms twice per revolution), and is currently a mere 190 light years away.

HD140283 has been baffling astronomers for more almost 2 decades now, ever since its age was calculated back in the year 2000 to be approximately 16 billion years - in other words, older than the universe itself! Well... thanks to Hubble, we have now refined those earlier estimates downward, and the star is currently thought to be 14.5 billion years old, plus or minus 0.8 billion years. This is one case where that "plus or minus" turns out to be extremely important! Subtracting the full uncertainty factor from the estimate gives us an age of 13.7 billion years, i.e., about as old as the universe itself. HD140283 must therefore be one of the very first stars ever to have formed.

Indeed, HD140283, now affectionately nicknamed "Methuselah" by those studying it and officially the oldest known star in the universe, fits the expectations of what such a star would look like. Its metallicity (the percentage of a star's mass made up of elements heavier than hydrogen or helium) is only about 1/250th of the sun's. Recall that the younger a star, the higher its heavy element content, due to "seeding" from preceding generations of stars gone supernova. (It is believed that the early universe contained no heavy elements whatsoever.)

Astronomers believe that HD140283 did not form in the Milky Way, but is instead a survivor of a long-lost dwarf galaxy that was sucked into and absorbed by our own galaxy about 12 billion years ago. Its highly elliptical orbit within the halo is testimony to this long-ago cataclysm. At the moment, HD140283 is passing through our sun's spiral arm at a speed of more than 800,000 miles per hour - so fast that it can actually be seen to change position against the background stars in Hubble images taken only a few hours apart!

At magnitude 7.2, HD140283 should be an easy binocular object, but is best seen through your telescope. WARNING! Starhop instructions follow! Start by locating the constellation Libra, and identify the two brightest stars, Zubeneschamali (mag 2.6) and Zubenelgenubi (mag 2.7) (Don't you just love those names?), a.k.a., Beta and Alpha Librae. Making a rough equilateral triangle with these two stars is the magnitude 3.9 Gamma Librae, over to the left. Using a line between Gamma and Beta Librae as the hypotenuse of a yet smaller right triangle, you can then locate the magnitude 4.6 star 37 Librae, which would mark the point where our imaginary 90 degree angle would be. (This second triangle would be hanging off to the left of the first one.) From here it is an easy star hop of approximately three full moons leftward and slightly down to our target, HD140283. There is no other star in the immediate vicinity even approaching this one in brightness, so there should be little difficulty in making a positive identification.

Just remember when observing this "dot" that you are looking back to the very beginnings of our universe. Quite a thought.

BOOK REVIEW: Objects in the Heavens, by Peter Birren

Amongst the most impossible questions to answer at a star party is "What is the best telescope? Which one should I buy?" Of course the best answer to that imponderable is "The best telescope is the one that you'll use." Well.. the same thing goes for handbooks, manuals, and star charts. The right question to ask is "Am I going to use this?" And as regards Peter Birren's Objects in the Heavens, the answer is an unqualified YES.

I saw this book advertised on Page 5 of the June 2018 issue of Reflector Magazine, and was sufficiently intrigued to check out the website (www.birrendesign.com). What I saw there convinced me it was worth a try, so I ordered a copy. I have to say it arrived in near record time.

First of all, the externals. The book measures 8.75X5.5 inches, so it is a very convenient size (unlike the mammoth 2 volume Night Sky Observer's Handbook published by Willman-Bell, my
go-to reference guide). I like the spiral binding - allows the pages to lay flat with nothing lost in the fold. I haven't taken it out in the field yet, but the paper does not appear to be dew resistant, so you might want to take precautions against it getting damp. The author uses his own idiosyncratic symbols for various objects, but I quickly got the hang of it, and found some of his innovations rather useful (such as making the distinction between binocular and telescopic objects). The star charts are for illustrative purposes only. The book might be best used in conjunction with Sky and Telescope's Pocket Sky Atlas.

Objects in the Heavens is divided into 3 major sections. The first is a very fine reference/introduction aimed at a novice audience. It's amazing how much is covered in such a small space (40 pages). It would be exhausting just to list the topics covered. Everything from explaining how various types of telescopes work to what is meant by right ascension and declination to a quick tutorial on how we got the constellations as they now exist, and literally dozens of other subjects as well.

Seven pages of the introduction are dedicated to the Moon. This is probably the weakest section in the book, but it's hard to see how it could have been otherwise. The Moon really requires a book to itself to do justice to the challenges of observing it. But I do give Mr. Birren credit for dividing his treatment of the subject by days after new moon. So he has a list of the major features sitting atop the terminator for each day. Unfortunately, the accompanying illustrations are just too small to be useful on their own. For the most part, I have no quarrel with the features he chose to highlight.

The introduction ends with 4 very attractive charts, one for each season.

The meat of the book is Section Two, a constellation-by-constellation listing of Deep Sky Objects (magnitude 10 or brighter) with brief, often amusing, descriptions of what you're looking at, accompanied by a chart of the constellation itself. The introduction says there are 830 objects identified in this book - enough to keep most stargazers busy for several years, if not a lifetime. I like the balanced nature of Birren's listing. It's not top heavy with galaxies or overly dominated by open and globular clusters. There are nebulae galore and enough double stars and even singleton stars to satisfy even a fanatic like myself. (Almost! I checked for some of my favorites, and was sad to find many of them them missing. But come on, there are countless thousands of the things up there viewable through the average telescope. So if Struve 2398 (one of my favorites) was omitted, I can't really complain now, can I?)

I was pleased to find Barnard's Star listed, but disappointed to not see Lalande 21185 in Ursa Major. What gives, Peter? How did you miss that one?

But on the flip side, there are more than enough listings that I had never heard of, which just goes to show that any list compiled by a single individual will never match another's. And that's a good thing.

The constellations are listed alphabetically and not in the order they appear in the seasons, just as they are in the Night Sky Observer's Handbook.

The final section is enough space to record 15 sketches of your own observations. You can order separately a second volume entirely devoted to sketching. (I did not, so I cannot comment on it.) I heartily endorse the author's maxim: "Trust nothing to memory!" Good advice.

Bottom line? Objects in the Heavens is value for money ($24.95), and I will definitely be consulting it when planning future nights out under the stars.