Date: November 16th, 2012
Title: Encore: The Jewel in the Harp
Organization: RapidEye Observatory – a private observatory in rural Lee County, NC http://www.rapideye.us/astro/RapidEye-ClearSky.html
Link: AAVSO Finder Chart http://www.aavso.org/vsp/?pickname=T%20Lyr
Bio: I’ve been captivated by astronomy ever since I was a kid, living in NW Colorado where the Milky Way was bright enough to read by. I can be found most clear nights in my pasture with either my 4.5″ SkyQuest, 10″ Deep Sky Hunter, 18″ Obsession, or one of my MANY pairs of Binoculars.
Today’s sponsor: This episode of 365 days of astronomy was sponsored by Clear Skies Observing Guides, a Modern Day Celestial Handbook. www.clearskies.eu ..Clear skies observing guides, or CSOG, is a new concept in visual amateur astronomy. The observing guides contain thousands of objects to observe through amateur telescopes, with matching tours for GOTO telescopes and matching AstroPlanner plan-files. CSOG allows you to target deep-sky objects and carbon stars you never observed before, night after night. Wishing astronomers around the world: Clear skies..!
This time of year in the Northern Hemisphere, Lyra the Harp is high over head shortly after sunset. It is an easily recognized and commonly visited constellation full of interesting objects. Epsilon Lyrae, commonly known as the double-double, is certainly a highlight at fall star parties. As is M57 or the ring nebula, one of the premier planetary nebulae in the sky. But for me, the real hidden jewel in Lyra is T Lyrae – a fabulous carbon star that looks like a deep red garnet.
So what is a carbon star? Late in a star’s lifetime its supply of Hydrogen starts to dwindle and it develops large amounts of elements heavier than Helium such as Carbon, Nitrogen, and Oxygen. The carbon tends to accumulate in the upper layers of the star, creating a thick sooty layer that blankets the star, obscuring much of its visible light. Light that does escape the solar soot is primarily red and infrared, with very little blue or yellow light escaping. This leaves a star thats color is perceived as anywhere from a deep blood red to a lighter, salmon or poppy pink color.
Being late in their stellar lifecycle, most carbon stars are also pulsating variables and will raise and lower their brightness by easily observable amounts. According to the American Association of Variable Star Observers, or the AAVSO, T Lyrae varies its visual magnitude between 9.2 at its minimum and 7.5 at its maximum. Also because they are variables, the AAVSO has amassed decades of observational and spectral data that can be charted, trended and used for research purposes. Visit them at AAVSO Dot ORG for more information about T Lyr as well as thousands of other variable stars.
While all Carbon stars are red, not every red star in the sky is a Carbon Star. Some, like Mu Cephei, also known as “Herschel’s Garnet Star”, Alpha Scorpii, also known as “Antares”, and Alpha Orionis, also known as “Betelgeuse” are famous, dazzling, bright, red stars that are late in their stellar lives; however, their spectral lines are quite different from carbon stars and their red color comes from a different mechanism.
Because the human eye is less sensitive to red light than white light, judging the brightness of carbon stars can be difficult. This is frequently referred to as the Purkinje effect. Depending on how dark adapted your vision is, this can make finding carbon stars difficult. On many occasions I knew I was in the right area of the sky and sweeping the area with a low power eyepiece would not yield any results. Then after performing a careful starhop in the finder scope and using the detailed AAVSO maps, switching to the eyepiece I would be rewarded with that little red jewel that I had probably overlooked 5 times while sweeping the area. This also makes finding T Lyrae difficult in binoculars, even though at 7.5 – 9.2 it should easily be in reach for most astronomical binoculars.
So how do you find T Lyrae? I’ve included a link in the show notes to the AAVSO Chart page for the star. There are several options you can select to get a larger or smaller chart, reversed image for refractors and SCT’s, so you can select the chart that is just right for your scope. Once you’ve located it a time or two using a chart, it is very easy to revisit by star hopping from memory. For me, the easiest way to find it is to locate Vega, Lyra’s brightest star. Then locate epsilon Lyrae, near Vega. T Lyrae is located on the opposite side of Vega from epsilon, by about the same distance. There isn’t a straight line between the three stars, but its is fairly close. You’ll know you are in the right area when you see a crooked line of 8th and 9th magnitude stars that is about one degree long. Your target is next to the middle of that line of stars.
I’ve observed T Lyrae with telescopes as small as 90mm and as large as 20” – it always looks beautiful. Larger apertures help pull out more color, but small scopes work fine with increased magnification. As magnification increases, the background darkens, giving greater contrast making the star and its color more easily visible. Also, when the star is on the dimmer end of its variable cycle, it tends to appear a deeper color of red, like a garnet on black velvet.
So the next time you are observing with your buddies and they are taking in the double-double or the ring nebula, ask them to swing the scope over to T Lyrae so they can see the hidden jewel in the harp.
End of podcast:
365 Days of Astronomy
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