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Salutations celestial sight seers! I'm David Fuller, welcome to Eyes on the Sky; what's
up this week?
At a visual magnitude of zero, Vega is the fifth brightest star in the entire night sky,
seen easily even from city locations. Though this star seems to steal much of the "brightness
thunder" from the other stars in the diminutive constellation of Lyra the Harp; the other
stars in the area seem to make up for it with fantastic color and double star configurations.
And many are not far from Vega itself. The star Sheliak in Lyra, here, is of intense
interest too, because despite appearing somewhat dim to our eyes at around 3.5 magnitude, it
is actually a double star system that shines as bright as 2000 of our Suns! And though
these two stars orbit far too closely to separate visually, they do eclipse each other from
our line of sight every 6.5 days, dipping from 30% to 50% in brightness as one stars
shines more brightly than the other, causing changes in magnitude with the pattern of eclipses.
But Lyra is full of interesting doubles.
With binoculars or a finderscope, start at Vega and move all of a degree and a half in
the direction of Deneb in Cygnus. This short hop leads to the star Epsilon Lyrae, which
can be seen in lower power optics as a double star. But these two stars each hold a secret.
This is where a larger aperture telescope, good optics, and a steady sky are required.
Because not one, but BOTH of those stars are each a double star themselves, though very
close together! This is the famous "Double-double" star, and it really is that easy to find,
but splitting both stars takes better optics and good skies.
Dark Sky Fact: Fully shielded lights that use motion sensors to turn on only when necessary,
and turn off when unneeded, are the most efficient way to light up a given area, and maintain
safety.
Now from Vega, head towards Altair, past 4.3 magnitude Zeta, on to Delta Lyrae -- actually,
Delta 1 and Delta 2. Delta 1 is the dimmer visually at 5.5 magnitude, but a hotter, blue
spectral class B star visible first on your way into this area. Just over 10 arc minutes
away is Delta 2, a 4.2 magnitude M-class red giant star that is much cooler, but closer
to us, which causes it to appear brighter. In addition to the striking visual contrast
there is a significant temperature difference: Blue Delta 1 is 18,000 Kelvin, while red Delta
2 is 5 times cooler at a mere 3,600 Kelvin. The magnitude difference also makes sense,
given that Delta 1 is 200 light years further from Earth, at 1100 light years distance,
while Delta 1 is 900 light years away. The color difference between them is like comparing
a propane torch and the glowing coals of a fire.
tBu there's more: But it will require a telescope of moderate to large aperture. Right where
these two stars are in the sky is an open cluster, alternately called Stephenson 1 or
Delta Lyrae 1. With a 4.5" scope, I could see about 10 stars in the immediate area;
not all are members of the cluster, which is rather loose and not-well defined, but
there are a dozen stars or so -- and likely more -- that were born out of the same gas
cloud around 60 million years ago, and are about the same age as Delta 1 Lyrae. Keep
in mind that Delta 2 is merely a foreground object here, and some other stars in the area
are as well.
Along The Ecliptic: Venus doesn't gain much in altitude or brightness this week, but does
scoot away from Gemini and towards Cancer over the course of seven days. Meanwhile,
Saturn is less than a half a degree from the 4.2 magnitude star Kappa Virginis in the southwestern
evening sky.
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.