When the change of seasons comes to the Upper Peninsula of Michigan
it hardly goes unnoticed. Gone is the plush vegetation of summer that covered
the forested
landscape; it has been replaced by a rather desolate outline of barren open
branches devoid of leaves. At first the new setting seems hopelessly abandoned,
but with
a closer look and some contemplation you discover that a haunting beauty
remains.
Such dramatic contrast is not the sole possession of the earthly
scene. The observable universe of the evening sky undergoes a similar transformation.
The densely populated
caverns of the Summer Milky Way are setting in the west, leaving only the
open figures of autumn's constellations that seem quite sparse in comparison.
One
look at the 84-hour exposure made by the Hubbell Telescope in northern
Adromeda
helps us to appreciate that this is not really the case, the sky teems
with celestial wonders unimagined. However, for the backyard sky-watcher with
much more modest
equipment, the autumn sky presents a challenge when compiling one's observing
list; even the seasoned observer may find the pickings slim. Including
binary
stars in with your "deep sky" targets, may help to fill the voids.
Binary Stars
The term "binary star" was coined
by William Herschel in 1802 to describe "the
union of two stars that are formed together in one system, by the laws of
attraction." Often
they are called double stars and they can be both technically challenging
and aesthetically pleasing. The former quality appeals to some and with practice,
binary star systems can be carefully measured for both separation (the distance
between the components) and position angle (the angle formed by a line plotted
due north from the primary star and a line plotted between the primary and
secondary stars). In time these measurements can reach a high enough level
of accuracy
to be used in determining the orbits of these systems. However, with the
exception
of some with very interesting and shorter orbits, I prefer the latter quality
of aesthetic beauty. I observe them for enjoyment and find some to be very
captivating. I'm not alone; even those who pursued extensive scientific studies
of binary
systems, on occasion, made heart felt exclamations over their beauty.
The
double stars I have chosen from many dwelling among the autumn constellations
are some of the most beautiful or interesting or both. Sixteen specimens
are listed by right ascension and a small finder chart and drawing are made
for each.
My hope is that you will enjoy them enough to include double stars as a regular
part of your observing list in the future.
The Target List
As you look over the target list, you might notice that all the primary
stars are bright enough to be seen with the naked eye from a dark viewing
site,
I can see all of them from front yard on dark moonless nights. This should
help
the
beginning observer, in that he can put his red dot, crosshair, or bullseye
right on the target. From a less-than-dark site you'll need to star-hop from
the stars
you can see. Also, you should be able to split all the pairs in a 3" telescope
and most in a 2"; that puts them in the range of the equipment of almost
every beginning observer. I am able to split all of them with my 80mm f/15
achromat refractor.
The constellations I have included are: Andromeda, Aquarius,
Aries, Capricorn, Cetus, Delphinus, Equuleus, Pegasus, Pisces and Triangulum.
Again, they are
all visible from my observing site at 46°+ latitude, so they should be
easy from most locations in the Northern Hemisphere. The star charts were
made using Guide
astronomy software and the drawings were made using Adobe Photoshop. With
the drawings, I tried to give a good idea of what you will see at the eyepiece,
however, the orientation of the two stars may differ from the drawing, depending
on what
equipment you are using.
The Targets
Let's begin in the West and work our way East.
Our first stop
is at Alpha Capricorni. The widest and only naked eye double on our tour.
The two stars, Alpha1 and Alpha2, together were named
Algiedi
by the
Arabs and the individual stars Prima Giedi and Secunda Giedi respectively.
At 48X, I see them both as yellow and just below Alpha1, it's faint
secondary is
a dim yellow. Actually both stars have companions, making this a double-double,
but within the narrow field of view of my long focus 80mm, I can only
view three stars at one time.
Alpha Capricorni can be used to help illustrate
the importance of limiting magnitude of an instrument in detecting faint
doubles. Alpha1 has a second
companion about
the same distance and direction as the one in my drawing, however it is
near magnitude 14, beyond the limit of my 80mm. It is also just beyond
the limiting
magnitude of a 6-inch telescope as famed double star observer William Smyth
mentions it in his "Bedford Catalogue". With reference to A1
and it's dim companion he says: "The telescope, however, shows it
to be multiple; but it requires an instrument of no small power to reveal
the most
minute point of light, which
long baffled my attempts to catch it. Indeed, when John Herschel first
wrote to me about it, in a letter of the 7th of October, 1831, the case
appeared
hopeless; but under clock-work motion, on a singularly fine September evening,
I caught
it in little evanescent flashes, so transient as to recall Burn's snowflakes
on a stream. ....its position angle was within estimation, but the distance
is nothing more than a vague guess." "The determination ........
may be reserved for one of the new grand telescopes, and will indeed be
a triumphant
achievement." It says a lot about Smyth's observing skills to even
glimpse a 14th magnitude star in his 5.9" refractor at Bedford. However,
the "triumphant
achievement" would come to S.W. Burnham who listed it in his "General
Catalogues of Double Stars" in 1874. Under the designation of BU 295
he says: "The faint star was added with the Washington 26-inch" So
what was just beyond the limiting magnitude of Smyth's 6-inch was "caught" and
measured by Burnham in a 26-inch. Limiting magnitude of an instrument can
be an important factor in splitting faint doubles.
About 2.5° south of
Alpha Capricorni is Beta. Dabih, as it is called, is nearly as wide as Alpha,
but is just beyond naked-eye visibility; making
it
a nice binocular double. In my 80mm at 48X it shows nice color contrast with
a
primary that is yellow and the secondary of bluish white. Smyth saw it as
Orange yellow and sky blue as did both Olcott and Flammarion.
 
Located in the snout of the Dolphin is Gamma Delphini - a
beautiful double star. It is one of the most colorful in our tour. It is
an exquisite sight
in my 80mm
at 96X, with subtle shades of yellow and blue. However, this double may show
the variations of color often noted by different observers viewing the same
object. For Smyth calls it "a beautiful double star" with a yellow
primary and a light emerald secondary, while Olcott notes a bluish-green
secondary to
this "beautiful object" and Flammarion, as well as Couteau saw
orange and green. This color difference is mentioned by Crossley in his "Handbook
of Double Stars". He states that " B appears to vary in colour;
it is given as yellow, green and blue, by different observers." What
colors do you see?
To the southeast of Delphinus lies the lopsided pentagon
of Equuleus, the
little horse. The western most star in this constellation is Epsilon Equulei.
I like
to use a bit more power on this double and so at 150X in the 80mm the primary
appears yellow-white and the secondary an ashy white. Olcott saw white and
blue and Smyth, white and lilac. Couteau states that it is a "Good test
for a 10-cm refractor" and is obviously referring to the 11" separation
of primary and secondary. Yet, Epsilon Equulei is in fact a triple star with
the
primary having a second, very close companion. The discovery of this dim
companion illustrates the effect that orbital motion has on the ability to
separate a binary.
In her book, "The System of Stars", Agnes Clerke uses Epsilon Equulei
to illustrate this. She writes: "Double primaries occur as freely as
double satellites; and their common centre of gravity presumably constitutes
the focus
of attraction for their remote attendants. ... Another specimen is Epsilon
Equulei, one of Herschel's pairs, the larger member of which was again divided
by Struve
in 1835. The feat had become possible through the progress of orbital motion,
the continuance of which has since rendered it easy." As orbital motion
caused the separation of Epsilon Equulei and it's dim companion to increase,
discovery was inevitable.
If Pegusus, the winged horse, were going to win a
race "by
a nose",
it would be Epsilon Pegusi leading the way. At 48X in my 80mm, the colors
contrast subtly as yellow and white. Olcott saw then as yellow and violet,
while Smyth
noted yellow and blue and speaks of a distant third member of violet color.
Enif was discovered by John Herschel and he also noted an unusual phenomenon
that
earned this double the nickname of the "Pendulum Star". Olcott
remarks: "Epsilon
Pegasi exhibits a phenomenon noted by Herschel; the pendulum-like oscillation
of a small star in the same vertical with a large one, when the telescope
is swung from side to side; merely and optical illusion of course." To
see this effect try bumping the telescope while viewing it.
The Water Carrier,
Aquarius, lies directly south of the head of the winged horse. The "Y" formation
in this constellation, commonly called the "Water
Jar", holds our next target. Zeta Aquarii is the center star of the
water jar and is one of my favorite doubles. What it lacks in color, it makes
up in
elegant symmetry. I can split them with my 80mm at about 90X, but I like
them best at about 200X; a pleasant view of two white stars of equal magnitude.
Like
a pair of headlights on a distant highway, these two twins sit almost exactly
on the celestial equator - declination 0°. Though Smyth notes them as
very white and white, some observers do see a trace of color in them. Webb,
for instance,
saw them as greenish-white and pale yellow. Couteau calls them a "good
test for a small refractor" and at a separation of 2.1" they are
at the limit of a 2-incher's resolving power. Try them with your 60mm, it
should be
a "good test" indeed. According to Crossley, Zeta Aquarii was first
discovered to be double by Christian Mayer in 1777 when it was about 3" in
separation and 18° position angle. Therefore, if you observe it at this
time you will be seeing it on the exact opposite side of the orbit from where
it was
at it's discovery.
94 Aquarius lies in pretty remote area near the left knee
of water carrier, but with a magnitude of near 5, it is still visible to
the naked eye on a dark moonless
night. To me at 48X the primary appears yellow/orange with a yellow white
companion and Crossley seems to agree noting them as yellow and ash. Yet
Flammarion saw
rose and blue and Smyth gives pale rose and light emerald, while Olcott merely
notes that the colors are contrasting. It is a lovely double, no matter what
colors you see.
The next constellation on our tour is Pisces, the fish. It
strings out underneath Pegasus and Andromeda and contains four of our target
doubles. The first
of which is 65 Piscium, a fairly tight yellow-white pair that can be split
at
48X, but
that I like the view at 150X. Flammarion calls them a delicate, rather luminous
couple; and being exactly equal in color and magnitude, "couple" would
certainly apply. Like two peas-in-a-pod, it is difficult to tell primary
from companion, but if you know you telescope view, you'll note the companion
northwest
of the primary star.
Psi Piscium is another very equal pair. At 48X they
split nicely into a silver-white pair of approximately the same magnitude.
When you look at them, try to imagine
they are just as they were when Struve measured them over 180 years ago.
It shouldn't be hard, cause they have not changed in separation or position
angle
since their
discovery. When Olcott wrote his "Field Book of The Skies" in 1929,
he said of Psi Piscium: "No change noted in 130 years"; so for
over 200 years now, they have remained 30" and 160°. In his handbook,
Crossley affirmed that they were a physical pair (a true binary system),
easy to observe,
but noting the unchanging physical properties he added - "yet the measurements
are very discordant". Over a hundred years later they still seem quite
odd. I think Smyth said it best when he remarked - " My observations
tend to show fixity."
About 14° to the south of Psi is another wide
double star - Zeta Piscium. Olcott calls it "a fine object" and
Smyth: "a neat double
star".
Though both are white in my 80mm at 48X, the secondary seems a different
shade of white, probably from the difference in magnitude. Couteau, in his
book "Observing
Visual Double Stars", notes that Zeta's secondary has a companion also,
making this a triple system. This third star in the system (C) is over magnitude
12 and is just 1 arcsecond from it's primary. With a magnitude difference
of nearly 6, this close binary would be very difficult to observe. In fact,
it was
discovered by S.W. Burnham using the 36" Lick refractor! Designated
BU 1029, Burnham states that "The measures of C cover a sufficient time
to show that the small star belongs to the system" and has a "slow
orbital motion",
but not as slow as AB. Of the wide pair he says: "The measures of the
wide pair (Struve 100) are very numerous and cover, first and last, more
than a century.
The early distances, however, are inaccurate and inconsistent, and the reliable
results commence with the measures of Struve. A few only of the measures
are given above, but sufficient to show the relative fixity of these stars." The
measurements in his catalog date back as far as 1832 and differ less than
an arcsecond in separation and less than a degree in position angle from
today - "fixity" seems
to describe this double as well.
Excuse me while a digress a little from
the west-to-east trek across the autumn sky and move a little further
east to pick up the fourth star in Pisces
- Alpha.
Alrisha, located at the intersection of the tail-fins of Pisces, is easily
seen with the naked eye at 4th magnitude. However, this is the one double
star on
our tour that is beyond the resolution of a 60mm telescope - in theory
anyway. Still, the Dawes limit of 1.9 for a 2 inch scope is a theory and
who knows,
on a perfect night with clean, sharp optics and a keen eye, you just
might detect
the evidence of a double star. You may not be able to split it cleanly,
but any elongation will indicate duplicity. Why not give it your best try?
Theories
are
made to be tested.
Olcott states that it is "difficult for a 3 inch
telescope"; I have
found it moderately challenging in my 80mm at 200X. At this power in a 3
inch, the colors are too dim to detect, but using his 5.9 inch refractor,
Smyth saw " a
splendid object" of "pale green and blue". Others have seen
a variety of colors and Crossley came to the conclusion that "both stars
probably vary in colour and brightness".
Our tour now "retrogrades" a
bit from Alrisha to two double stars in Aries, the ram. It is not an impressive
constellations made up essentially
of
three stars; Alpha, Beta and Gamma. It is Gamma or Mesarthim that we take
a look at next. Once again, in the 80mm, we find perfectly matched twin stars
of the
same magnitude and both silvery white. They can be split at 48X, but I feel
the best view to be at 150X. They are also unique in that they have, in effect,
two
position angles; 360° & 0°. Yes they sit one on top of the other,
like the makings of a snowman; kind of a prelude of what is soon to follow.
Gamma Arietis was first found to be double back in 1664 by Robert Hooke.
After commenting
on the existence of double stars he says: "Of this kind, the most remarkable
is the star in the left horn of Aries, which, whilst I was observing the
comet which appeared in the year 1664, and followed till he passed by this
star,
I took notice that it consisted of two small stars very near together; a
like instance
to which I have else met within all the heavens."
About 3° northeast
of Gamma is Lambda Arietis. With this double we return to one that has very
contrasty colors. It is a lovely double that I can easily
resolve it in my 80mm at just 48X, where it shows a striking contrast of
yellow and bluish-green. Smyth agrees with my perception, but Olcott saw
no yellow tint
and lists "white and blue". It was discovered by William Herschel
in the late 1700's, one of 848 pairs that he would eventually find. He was
so enthusiastic
about this "new" area of study that he was inspired to write: "The
subject has already proved so extensive and still promises so rich a harvest
to those who are inclined to be diligent in the pursuit, that I cannot help
inviting every lover of astronomy to join with me in observations that must
inevitably
lead to new discoveries".
Almach (Gamma Andromedae) is one of the most
beautiful objects in the sky. It is at the top of my observing list whenever
it makes it appearance in
the evening
sky. I have found myself staying up later that I wanted to on summer nights,
waiting for it to clear the trees, so that I can get a glimpse. I'm not alone.
Olcott, in his book "In Starland with a Three-inch Telescope",
wrote, "Gamma
Andromeda is one of the most beautiful double stars in the heavens; the contrasting
color of the two stars is very fine". He gives the colors as "yellow
or orange and greenish-blue". Couteau writes, "One of the most
beautiful systems, orange and emerald". Smyth calls it "a splendid
double star, A (primary) orange colour and B (secondary) emerald green; and
of these colours
I feel pretty positive, although the high authority of Herschel and Struve
has pronounced them to be yellow and blue". In my 3 inch, I see them
as bright yellow and deep blue, colors that hold up at 96X, 120X or 150X.
More then any
other star,
Gamma Andromeda gives me the feeling that I'm am seeing a star
and it's planet. It's an illusion, but a very nice one and it is enhanced
by the
fact that the "planet" has a "moon". Crossley wrote: "The
duplicity of (Gamma) B was discovered by Otto Struve in 1842." Smyth
verifies this when he wrote: "Mr. Bailey put in my hand a letter which
he had received from Mr. Struve, in October, 1842, announcing the unlooked
for tidings that he
had detected Gamma Andromedae to be a triple, and that the companion is composed
of two stars of equal size, separated by an interval of less than 0.5 arcseconds." At
that distance, I will probably never see the secondary's companion, but still,
it nice to dream.
Triangulum is another three-star constellation which forms
a triangular shape directly south of Gamma Andromeda. Iota Tranguli is directly
south of the "triangle".
It is another lovely double and is the third double star in a row that is
yellow and blue. To be specific, it appears yellow and dirty blue in my 80mm
at 120X.
It is the only double star cited by Olcott for Triangulum and he gives the
colors as "yellow and blue", calling it "an exquisite pair".
Smyth on the other hand, gives topaz-yellow for the primary and green for
its companion
and Flammarion called it "gold yellow and blue green, very pretty." With
a separation of just 4 arcseconds, it is a tight double, but easily split
by the 80mm.
Cetus, the whale, holds our final sample of autumn doubles,
Gamma Ceti. It is located in the whale's head, 10° due east of Alpha
Piscium and north of the famous variable, Mira. Called Kaffaljidhma by the
Arabs, Smyth notes
that the "colours
are finely contrasted"; a pale yellow primary and blue secondary and
that is how they look in my 80mm at 150X. He describes them as a "beautiful
object" in
his 5.9" refractor and they make a good test for a 3". Olcott calls
it the "finest double in this region and Flammarion says its "pale
yellow and blue", a "charming" double.
Conclusion:
Flammarion's use of the word charming could apply
to most doubles stars. They are the jewels of the evening sky and each pair
beacons to be examined
with
care. It is estimated that about 70% of stars are mulitiple in nature,
so there are
a vast number from which the observer may choose. The most prolific double
star observer, F.G.W. Struve, used the Dorplat 9 1/2" achromat over
a 13 yr. period to complete a sky survey of 120,000 stars and cataloged
the measurements
of over 3300 double stars; a feat that required him to examine an average
of 400 stars per hour! I am not encouraging anyone to engage in such an
endeavor, but rather to observe the more notable ones and get to know them
personally.
Writing about the observation of double stars in her book, "The System
of Stars", Angnes Clerke said: " It would be better to make intimate
acquaintance with one than to know a score superficially." Perhaps
you might consider adding more than one, to your observing list.
References:
1.The Bedford Catalog - Wiliam H. Smyth (1844)
2.Field Book of The Skies - William T. Olcott (1929)
3.In Starland with a Three-Inch Telescope - William T. Olcott (1909)
4.Observing Visual Double Stars - Paul Couteau (1923)
5.Stars and Curiosities of The Sky - Camille Flammarion (1882)
6.A General Catalogue of 1290 Double Stars - S.W. Burnham (1900)
7.A Handbook of Double Stars - Crossley, Gledhill & Wilson (1879)
8.The System of Stars - Agnes M. Clerke (1905) |
