sign in sign up
<<
Home , Beta Lyrae, Gamma Lyrae

oV\,e ctooc{ Torrget w~tVi SoVVte otViey s~g Vits wortVi see~v\'g wVi~Le You'ye ~V\, tVie Ne~gViboyVioool

August PLClV\,etClYkj NebuLCI M5T(n,e RLV\,g NebuLCI) wLtv, sLde trL-ps to til dee-p red ~til rboV0 sttil r tilV0d til ~oLorfuL doubLe -ptilLr

Planetary nebula M57 - The - is a favorite target for public outreach, where it's invariably described as "a smoke ring in the sky." The nebula lies conveniently between Sulafat () and Sheliak (), the forming the bottom of the parallelogram in the , The Lyre. It sits a bit off-center between those stars, but almost exactly at the midpoint between Sheliak and a mag 5.2 just west of Sulafat.

The nebula formed 6,000 to 8,000 ago, when a red began to puff off its outer layers as it slowly ran out of fuel and approached its nuclear death throes. All that remains of the star is a magnitude 14.8 white dwarf, visible only under extremely steady skies with at least a 10 inch telescope (preferably at least 14 inches) and very high magnification (it usually takes 400x or more) - and even then it'll probably pop in and out of visibility.

• • ega Area surrounding M57 Stars to mag 6 • North at top • I

Sulafat j 1 I •

• . l 1 The nebula itself is a much easier target. Although it's just a blurry "star" in binoculars, it can be seen in scopes as small as 3-4 inches. However, the best views come in 6 inch or larger instruments, where the nebula's ring shape is evident. In the eyepiece, the Ring will be a monochrome gray image, since the red­ orange and blue-green colors seen in long exposure photographs are too attenuated for our eyes to pick up in real time. While you're in the neighborhood, take a moment to enjoy a deep-red carbon star to the west of the parallelogram, and a colorful double pair to the east of it.

The carbon star, T Lyrae, can be found near , the brightest star in Lyra (and the fifth brightest in the entire sky). As the finder chart below shows, you'll follow a line of mag 7 stars to a mag 8 triangle, where you'll find T Lyrae perched between two of the triangle's vertices. With a magnitude range from 7.8 to 9.6, T Lyrae is far from the brightest carbon star, but it is more reliable than most when it comes to displaying the deep red color that characterizes that class of stars . •• .. ..

/ Struve pair

\ .. (/ : \ . o i Zeta • 0 . . • One star .. \ ,. i . • • \ ( Two stars eo • 0\0 .. \. Three stars .! • • •• \ SUlafatp \ • . \ . . \' . • • l "'. • • • • / e • /

o e o e

Finder charts: S°field, stars to mag 8.75 (left) / mag 8 (right), magnitudes shown, decimals omitted, unreversed image, North at top

Now jump across the parallelogram to hunt down tonight's double pair, Struve 2470 and Struve 2474, from the catalog of double stars compiled by F. G. W. Struve at Dorpat University, Estonia, in 1827. Starting at the parallelogram's lower east corner, you'll follow a trail of roughly equal steps, from Sulafat to a group of three stars, then a group of two stars, then a single star, and a half-step farther to the double pair.

The two Struve pairs are separated by slightly more than 10 arcminutes, so both of them will fit nicely in a field about a third of a degree wide. Struve 2470 is a cool blue-white pair comprising a mag 7.0 primary located 14 arcseconds away from a mag 8.4 secondary, while Struve 2474 presents a much warmer golden­ orange pair, with a mag 6.8 primary 16 arcseconds from a mag 7.9 secondary. Use 60x or more to split both pairs cleanly.

The Struve pairs are similar to each other in primary and secondary magnitudes, separation, and position angle - virtually identical twins, except for their colors. And in contrast to Lyra's more famous Double Double (), whose all-white star pairs are perpendicular to each other, the stars in the Struve pairs are almost perfectly parallel: their respective position angles are within 5° of one another.

Rick Gering / NAA Public Outreach August 2019

------