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Salutations celestial sight seers! I'm David Fuller, welcome to Eyes on the Sky; what's
up this week?
Look to Cassiopeia, a medium-sized "M" shape composed of several 2-nd and 3-rd magnitude
stars, high overhead to the north in the evening hours. These five stars have quite the distance
differences too; we just happen to be in the right spot where they form an "M" shape from
our perspective (or a W shape, depending on the time of year and tilt of your head!).
Between Shedir and Gamma is a 3.5 magnitude star, somewhat closer to Shedir. It should
be visible naked eye from most locations. Train a telescope this way, and push up the
magnification a bit to separate the 11 arc seconds apart components of Eta Cassiopeiae.
Other than the subtle color difference, what's so interesting here? Well, the primary star
is VERY much like our Sun. Eta Cas is also G-spectral class, and contains 97% of the
Sun's mass, and is 101% of its radius. Plus, it's only 19.4 light years away, in our stellar
backyard. That makes it a lot like our Sun's twin, right? Well... not quite. More on that
in a moment.
Dark Sky Fact: A fellow amateur astronomer on reddit wrote to me, saying, "I called the
city, contacted a council woman and finally the utility about a streetlight. I emphasized
sleep and power consumption and the primary reasons for the request. Great news! The utility
just put up a shield." Get involved -- YOU can make a difference too!
The primary of Eta Cassiopeiae is what is called a "metal poor" star, meaning it is
low in elements other than hydrogen and helium. Due to that, it likely doesn't have planets,
as most stars found with planets have higher metals content. But if there were planets
there, then the smaller, K-class dwarf star that orbits it every 480 years would appear
as bright as 5 full moons in the sky of an Earth 2 planet. We can admire the color difference
of these two stars from here on Earth, and remember the light leaving them was sent 19.4
years ago, touching our retinas today.
Another double star well worth pursuing that's somewhat out of the way is Struve 3053. Starting
at Gamma, look for where Kappa Cassiopeiae is and, centering that star, prepare to hop
to the other side of the finder's field of view. But... note how this 4.8 magnitude star
next to Gamma is just off that line? Follow THAT line more closely, but estimating double
the distance from Kappa. That will place you at this little grouping of a half dozen or
so 6-th and 7-th magnitude stars. The one closest to Cassiopeia's "M" shape, this one,
is Struve 3053, and it's a lovely double star that is also a binary system. At over 2000
light years distance from us, their distance even from each other is considerable -- around
one-seventh of a light year. But to us, visually, the color contrast is what is so pretty to
see, and worth seeking out in this somewhat-off-the-beaten-path location. Again like our Sun, it has a G-class
primary and is similar in mass, while the A-class secondary is rather small, but much
hotter at 9,000K. You should see a lovely contrast between these two stars, though actual
color perceptions of them vary by observer. Looking for more colorful doubles in Cassiopeia?
How about binoculars-visible WZ Cassiopeiae, found less than two degrees away from Caph.
Finder charts and more info on finding these and more double stars in Cassiopeia will be
at the home page of eyes on the sky dot com this week.
Along The Ecliptic: Jupiter has begun retrograde motion in Gemini, and sits well above the
horizon for good observing now by 11 pm. At high magnification late in the evening, Venus
sports a lovely just-under-half crescent shape, while on the morning side, Comet ISON will
be within a few degrees of Porrima on the 12-th and 13-th, headed towards Spica on the
17-th and 18-th. Check out all the other comets Eyes on the Sky highlighted last week too!
That's all for this week. Keep your eyes on the sky and your outdoor lights aimed down,
so we can all see, what's up. I'm David Fuller, wishing you clear and dark skies.