Triangulation

Every stargazer knows the Summer Triangle. Heck, it's like the Big Dipper or Orion. Just one of those things up there that we all take for granted, not really thinking about them. "Oh, there's the Triangle. Must be summer." And on we go.

But let's take a moment to really explore the obvious. What exactly are those stars which make up the Summer Triangle? First off, what are their names? From north to south, they are Deneb (Arabic for "tail"), Vega (Arabic for "falling") and Altair (Arabic for "flying eagle"). They are, respectively, the 19th, the 5th, and the 12th brightest stars in the entire sky. That is, at least as seen from the Earth. In and of themselves, their order in descending brightness would be Deneb, Vega, and Altair. In fact, although Deneb appears to from our vantage point to be the dimmest of the three, it is one of the brightest stars in the entire Milky Way Galaxy, shining with a luminosity of 200,000 Suns (yes, you read that correctly). Only its enormous distance from us makes it appear less bright than otherwise. Vega, which boasts a luminosity of 40 Suns, is but 25 light years distant, making it appear to be the most brilliant member of the triangle. And bringing up the rear, Altair shines out with a radiance of a mere 10 Suns, but at 16.75 light years, it is the nearest of the three.

So let's start with Deneb. "Tail" is certainly an apt name for this star, as it marks the tail feathers of the celestial swan Cygnus (Albireo being the beak). In addition to its fantastic brilliance, this star is HUGE. Were it our own star, our poor Earth would be just grazing its surface in its present orbit. Ouch! Deneb weighs in at a little less than 20 solar masses, but is spewing out into interstellar space roughly the equivalent of one Earth mass every 500 years. Currently a blue-white supergiant, astronomers believe that Deneb with ultimately expand even further, evolving into a red supergiant before collapsing in on itself and going supernova. But that's a few million years into the future, so there's no immediate threat to our lovely summertime asterism.

Next on our list is Vega, the brightest (to us) of the three. Vega has quite a history to it. It used to be the Earth's North Star (14,000 years ago), and will be again in about another 13,000 years. (It will be so much easier then to do polar alignment, with such a bright North Star.) It was the first star (other than the Sun) to be photographed, and the very first to have its spectrograph taken. At about 500 million years old, Vega is quite the youngster. But due to its mass (about twice that of the Sun), it is racing through its time on the Main Sequence. In another half billion years, it will begin to swell into a red giant before losing much of its mass in the form of a lovely planetary nebula. (So stick around!)

Vega and the Sun to scale. Note the enormous equatorial bulge on Vega.

Vega rotates so quickly (once every 12.5 hours) that it is very near the point where it would tear itself apart from centrifugal force. This was hidden from astronomers until recently, since we are looking down directly onto one of Vega's poles, and cannot observe its squashed shape directly.

Vega is surrounded by what appear to be multiple discrete disks of dust and small bodies, possibly in the process of coalescing into planets. So we may actually be observing a solar system in the very act of creation!

Last but not least on our list is Altair. Those of you who are my age, or are fans of 1950s B-grade science fiction movies, will recall that Altair was the parent sun of the "Forbidden Planet" in the movie of that name - home to the mad scientist Morbius and his beautiful daughter Alta, Robby the Robot, and the Monsters from the Id.

A Monster from the Id

In our far more boring reality, Altair is a fairly typical main sequence star. It is somewhat less than twice the mass of our Sun and shines at 11 times its brightness. Like Vega, it has an extreme rotation rate, spinning on its axis once every 9 hours. This results in an equatorial diameter a full 20% greater than its polar measurement.

Only 17 stars other than our own Sun have ever been imaged as anything other than a point source of light. Below is a 2007 image of Altair taken in the infrared. Note the oblateness. And unlike Vega, we are not looking down on one of the poles.

So now summer's most prominent asterism ought to be more than just a triangle. Its component stars are fascinating individuals, which are worth getting acquainted with.

Pure Magic

We all have as observers different reasons why we track down different objects. Sometimes it's because this or that star is intrinsically interesting, or because it possesses one or more superlative (the biggest, the closest, the oldest, the furthest, etc.). Sometimes it's because the object is bright and splashy, and fills one's field of view with all sorts of complexities.

30 Cygni off to the upper left - 31 Cygni A and B off to the lower right

But every now and then we check out this or that deep sky object because.. well, darn it, because it's beautiful! Such is the case for Omicron Cygni. It's not just that their arrangement is aesthetically pleasing - their brilliant colors (bright gold and electric blue) rival those of the more famous (and nearby) Albereo.

Another view of 30/31 Cygni, showing off their colors

Now Omicron Cygni isone of the more confusing appellations up there, because several stars in Cygnus all go by that  label. Much better to use the Flamsteed designations 30, 31, and 32 Cygni, all of which make up "Omicron Cygni". Confused? So am I.

But there's more to Omicron Cygni than a pretty picture (although that's quite enough). The stars are interesting in their own right. 30 Cygni is a blue-white giant star, 610 light years distant, shining with the radiance of 324 Suns, making it a magnitude 4.83 star to our view. Nearby (visually, at least) 31 Cygni is an easily splittable binary. Despite its apparent nearness to 30 Cygni, the 31 Cygni system is 880 light years from our Solar System, so the 2 are actually separated by 270 light years. 31 Cygni's A component is an orange supergiant, 4,300 times brighter and 200 times the size of our Sun. Its dimmer B companion appears to different observers as either bright blue or "dirty" white. The three stars, although in actuality quite distant from each other, make up an attractive apparent triple star due to a chance line of sight alignment.

32 Cygni at upper left, 30 and 31 at bottom right

Meanwhile, 32 Cygni sits off about 1 degree to the north, completing the view through any eyepiece with a moderately wide field of view. At 1,100 light years away, it is the most distant of the "Omicron" stars in Cygnus. 32 Cygni is a spectrographic binary. (Its components cannot be separated visually.) The A component of this system shines with a luminosity of 6,600 Suns and is bright orange. Meanwhile, its poor B companion star has to make do with only 300 times the Sun's luminosity, and by itself would be a blue-white main sequence star. The 2 components make up an eclipsing binary, similar to Algol over in Perseus. Because the plane of the stars' orbits is precisely aligned with our line of sight, we can spectrographically study the solar wind of the primary star during each eclipse. From these observations, astronomers have concluded that 32 Cygni A is losing an incredible full stellar mass every 77 million years. Wow.

By the way, the colors in the above image do not do justice to the glorious view one gets through the eyepiece. I never fail to spend a minute or three just drinking in the view whenever Cygnus is high in the sky. Don't miss it this summer!

Mirror, Mirror...

Ever wonder what our Sun would look like, if you were observing it from outside the Solar System? Well, take a gander at HIP 569498, over in Draco.

This magnitude 8.7 star, at 208 light years away, is the closest analog to the Sun that we know of in the entire sky. Its mass is practically identical to the Sun, the difference being basically a rounding error (1.02  ± .02 solar masses). Its surface temperature is only 17° Centigrade higher that the Sun's (5521° vs 5504°). Its radius is a mere 9,000 km less than the Sun's (687,000 vs 696,000). Most importantly, its lithium content is identical to that of the Sun to within observational parameters. Lithium content is one of the markers that varies most widely from star to star, so an identical measurement is amongst the rarest of the rare. The two stars share many other close similarities as well.

But it is no solar birthmate. HIP 569498 is approximately one billion years younger than the Sun and shares no common orbital parameters (about the galactic center) with the Solar System.

HIP 569498 also apparently possesses no "hot Jupiters", so it is entirely possible that one or more Earthlike worlds exist within the star's habitable zone.

So take a few moments to contemplate this "dot" in the northern skies, and imagine some stargazer on a world 208 light years away looking in our direction. He would be seeing exactly what you are.

By the way, HIP 56948 has two very unofficial names other than its catalog listing. They are Intipa Awachan ("Sun's Twin" in Quechua), and Zilia ("Jealous" in ancient Greek). How unofficial are these monikers? They are the winners of a New York Times readers' poll conducted in 2007, so give them all the respect (that is, very little) that they're due.

HIP 56948

The Music of the Spheres

Seven poets sing of the stars:

Look thou no further, but affix thine eye 

On that bright, shiny, round, still moving mass, 

The house of blessed gods, which men call sky, 

All sow'd with glist'ring stars more thick than grass, 

Whereof each other doth in brightness pass.

(Edmund Spenser)

The infinite shining heavens rose 

and I saw in the night

Uncountable angel stars

Showering sorrow and light.

(Robert Louis Stevenson)

Look how the floor of heaven

Is thick inlaid with patens of bright gold.

There’s not the smallest orb which thou behold’st

But in his motion like an angel sings.

(Shakespeare)

The heavens declare the glory of God

And the firmament sheweth his handywork.

(King David (the Psalms), KJV Translation)

BEND low again, night of summer stars.

So near you are, sky of summer stars,

So near, a long arm man can pick off stars,

Pick off what he wants in the sky bowl,

So near you are, summer stars.

(Carl Sandburg)

Look at the stars! look, look up at the skies! 

O look at all the fire-folk sitting in the air! 

The bright boroughs, the circle-citadels there! 

Down in dim woods the diamond delves! the elves'-eyes! 

(Gerard Manley Hopkins)

As I watch the bright stars shining, 

I think a thought of the clef of the universes and of the future. 

A vast similitude interlocks all,

All spheres, grown, ungrown, small, large, suns, moons, planets,

All distances of place however wide,

All distances of time, all inanimate forms,

All souls, all living bodies though they be ever so different, or in

different worlds,

All gaseous, watery, vegetable, mineral processes, The fishes, the brutes,

All nations, colors, barbarisms, civilizations, languages,

All identities that have existed or may exist on this globe, or any globe,

All lives and deaths, all of the past, present, future,

This vast similitude spans them, and always has spann’d,

And shall forever span them and compactly hold and enclose them.

(Walt Whitman)

Magnus Frater

I'll be on the road for the next two weeks and away from my computer, so I thought I'd sign off (for now) with one more posting, this one about our own Sun's probable sibling, born out of the very same cloud of gas.

From left to right

90 Herculis, HD 162989, and HD 162826

I am speaking, of course, of HD 162826 in Hercules. This star is currently 110 light years from our Solar System, and has an apparent magnitude of 6.7. Its chance alignment with two slightly brighter stars, HD 162989 (magnitude 6.04),  and 90 Herculis (magnitude 5.16) is a huge aid in finding it. The 3-star asterism lies approximately halfway between super-bright Vega and the globular cluster M92 and just three degrees north of Theta Herculis (magnitude 3.85). It is ridiculously easy to find through binoculars. Theta Herculis is a naked eye star, to the left of the northwest corner of Hercules' "Keystone" (which contains the mighty M13 globular). Find that, and place it at the lower edge of your binocular field of view. The 3 stars shown in the above image will be near the top of that same field of view. [see footnote] The star on the far right is the one you're looking for. It's that easy!

Red arrow points to HD 162826

So why do we believe that HD 162826 was born in the same stellar litter as our own star? Three reasons:

1. It is the same age as our Sun (4.6 billion years).

2. Its chemical composition is a close match to the Sun, especially in elements that typically vary wildly between different stars, such as barium and yttrium. There are only 30 stars known in the entire Milky Way galaxy that are as close a match to our Sun as HD 162826.

3. It has been calculated (by computationally "winding back the clock" of the orbits about the galactic center of HD 162826 and the Sun) that 4.6 billion years ago (that is, when the two stars were born), they pretty much occupied the same space.

HD 162826 may indeed be the Sun's litter mate, but it is no twin. It is 15% more massive than our star and shines at an absolute magnitude of 3.92 (as compared to 4.83 for the Sun). If our Earth were circling round HD 162826, it would have be orbiting at a distance of Mars to be the same temperature.

Hmm... HD 162826 is a rather awkward moniker for so close a relative. It was a pain typing it nine times for this posting. Considering its mass, perhaps we ought to just call it "Big Brother" (or, more formally, we could use the Latin Magnus Frater).

Footnote: This assumes the top of your field of view is to the north. At the time of this posting (early July), HD 162826 will be very close to the zenith, so your own orientation may be quite different. So with that caution, let us say that the 3-star asterism will be to the north of Theta Herculis in your binocular field of view, and leave it at that.

Seeing Double Double

Epsilon Lyrae, the "Double Double"

We all of course know of the iconic Double Double (Epsilon Lyrae) next door to brilliant Vega. Many of us use this star as a test of our instrument's resolving power, or of the steadiness of a night's air. But have you ever taken a look at the other double double, over in Boötes? I am speaking of Iota and Kappa Boötis, or Asellus Secundus and Asellus Tertius (a.k.a., 2nd and 3rd Donkey Colts). Not a true "double double", since Iota Boötis is a mere 95 light years away, whilst Kappa Boötis stands off at more respectable 151 light years. A chance line of sight alignment is what allows us to see them side by side.

Iota and Kappa Boötis 

As sketched by someone calling himself "asteroid7" on Cloudy Nights

Both both components of this charming mashup are themselves doubles - and easily splittable ones at that. The A and B components of Iota Boötis are separated by 38.8 seconds of arc and 1130 AU of actual distance. (A single orbit of the two stars about a common center takes a whopping 24,000 years!) Together, they have an apparent magnitude of 4.75 making them a naked eye star. Meanwhile, the two components of more distant Kappa Boötis (known as Kappa-1 and Kappa-2) are separated by a tighter 13.5 seconds of arc and a mere 640 AU of actual distance. They orbit each other once each 8700 years, and are themselves each double stars (making Kappa Boötis a true "double double", but observable as such only spectrographically). The combined apparent magnitude of the entire Kappa Boötis system is 4.53, remarkably close to that of Iota Boötis.

As usual with double stars, different observers report different colors, so I won't "poison the well" here, and allow you to come away with your own impressions.

Iota and Kappa Boötis are the two stars at the top right of this rather simplified star chart

Zimiamvia

They sat there till the shadows crept over the lawn and up the trees, and the high rocks of the mountain shoulder beyond burned red in the evening rays. [Lessingham] said, "If you like to stroll a bit of way up the fell-side, Mercury is visible tonight. We might get a glimpse of him just after sunset.

A little later, standing on the open hillside below the hawking bats, they watched for the dim planet that showed at last low down in the west between the sunset and the dark.

He said, "It is as if Mercury had a finger on me tonight, Mary. It's no good my trying to sleep tonight except in the Lotus Room."

Her arm tightened in his. "Mercury?" she said. It is another world. It is too far."

But he laughed and said, "Nothing is too far."

E.R. Eddison, The Worm Ouroboros

Mercury and Venus as seen from Idaho, earlier this year

Image by Kris Hazelbaker

The above passage from The Worm Ouroboros is one of the most beautiful accounts of naked eye planetary observation I have ever read. It never fails to move me, especially after an evening like tonight. I had driven out to a nearby civic center that has a large open space behind it with a relatively clear western horizon. I knew that Mercury would be putting in his best evening appearance for the entire year, and despite the oppressive heat and clouds of mosquitoes, I walked out into the middle of that field and drank in the steadily darkening sky, which ran the spectrum from brilliant pink on the horizon to yellow at the tree line, up to pale blue just above the treetops to a deep blue where brilliant Venus reigned supreme, reminding me of Edmund Spenser's description of her:

Fayre childe of beauty, glorious lampe of Love
That all the host of heaven in rankes doost lead,
And guydest lovers through the nightes dread,
How chearfully thou lookest from above.

(Epithalamion, lines 588-589)

(If you have never heard Ralph Vaughan Williams' heartbreakingly beautiful setting of these words to music, you owe it to yourself to listen to it, Here: https://www.youtube.com/watch?v=QKaAtuEe_sQ Begin at 20 minutes 12 seconds in, and be sure to not miss the full chorus breaking in at 21 minutes 34 seconds.)

The sun had set at 8:30, but I couldn't see anything of Mercury, even through my 8X56 binos, until 9:04 - pretty much right where I expected to find him (a little lower, maybe). The humid atmosphere was distorting the view a bit. Mercury was a distinct yellow instead of its usual pristine white, and it actually twinkled. (Planets aren't supposed to do that!) I hadn't brought along my telescope, so both planets remained glittering points of light.

By 9:12, Mercury had brightened (or, more accurately, the sky had darkened) to the point where he could be seen naked eye, albeit only intermittently, and with averted vision. But by that time, I was being eaten alive, and decided to beat a retreat to the land of air conditioning, glancing up at Jupiter on the way to the car.

Mercury and Venus as seen from North Carolina

Image by Nicolas Holshouser

Bursting with Doubles

The constellation Boötes is pretty sparse when it comes to anything to observe. It contains only one globular cluster (NGC 5466), which by all accounts is a pretty poor example of the breed. Sky and Telescope's Pocket Sky Atlas lists only 5 galaxies within its boundaries, none of which are anything to write home about. Perhaps it is fitting that Bootes is home to the great Boötes Void, a 250 million light year diameter bubble of nothingness - no stars, no gas, no galaxies, and apparently no dark matter. Just nothing. (Obviously not a good target for observation!)

But what Boötes lacks in the splashier DSOs is more than made up for in its fine collection of double stars, several of which (such as Izar, a.k.a., Epsilon Boötes) routinely make the lists of "must see" doubles.

Struve 1835, and companions

But today I intend to focus on a lesser known example, Struve 1835. Located near the extreme southern edge of the constellation, almost due south of bright Arcturus and not far from the boundary with Virgo there lies an attractive chain of three stars, slightly curving to the northwest. The stars making up this asterism gradually increase in magnitude as you progress up the chain, making it lovelier still. The "bottom" star (HD 126271) has an apparent magnitude of 6.19. The middle star (HD 126200) shines at 5.95, while Struve 1835 has a combined magnitude of 5.12. All by itself, this beautiful trio is worth a glance or two.

Hmm... This 3-star asterism is currently unnamed. Let's see, we already have Brocchi's Cluster (the Coathanger), Herman's Cross, and Kemble's Cascade. Why not Prokop's Parade? (Alliteration is always a plus!)

But the real gem is that brightest star at the top. Pump up the magnification, and you'll split Struve 1835 into its component members. Descriptions vary enormously as to what colors different observers see. Some see no color at all, just two unevenly matched white stars. At least one observer has noted "2 yellow stars". But the most common description is of a bright blue primary with a dimmer secondary of uncertain hue, ranging from gray to purple.

I was unable to find an image of this star on the internet, but I did come across this very fine sketch (below).