Subtle but splendid
Whether you observe alone from a city backyard or with hundreds of others at a star party, Cygnus holds treasures galore. Summer's magnificent celestial swan appears best as it soars overhead on August evenings. Cygnus has a host of colorful double stars, none more famous than Albireo. Also known as Beta (b) Cygni, and labeled as such on the circular star map on the facing page, it marks the head of the swan. Without doubt, Albireo is the most lovely colored pair in the northern sky: a blue sapphire offsetting a brighter yellow topaz.
Keep these colors in mind and sweep your scope northeast past 2nd-magnitude Epsilon (e) Cygni to 61 Cygni. Staring back at you in a low-power eyepiece will be a pair of yellow-orange stars, not quite equal in brightness. Bump up the power a bit and take them slightly out of focus to show off their true colors. Most people judge their hue to be deeper than Albireo's topaz.
This star system holds a special place in the history of science because it was the first to have its distance measured, expanding our notions of just how big the universe might be. In 1838, German astronomer Friedrich Bessel measured subtle changes in its position over the course of a year, reflecting our changing perspective as Earth revolves around the Sun. Using simple geometry, Bessel concluded that 61 Cygni lies some 10.3 light-years away. The modern value stands at 11.4 light-years, making it the fourth-closest naked-eye star system after Alpha Centauri, Sirius, and Epsilon Eridani.
Just 1[degrees] northwest of 61 Cygni lies another interesting pair. Sir William Herschel, the father of deep-sky observing, discovered this duo and cataloged it as H IV 113. Although not as glorious as Albireo, the brighter component appears a striking blue in contrast to the subtle yellow of the secondary.
The mesmerizing Veil
If you head to a star party this summer, ask the owner of a large telescope to show you the Veil Nebula in an OIII filter (pronounced oh-three). Considered a challenging object for 6- and 8-inch scopes back in the 1950s and '60s, the Veil shows impressive structure in a 12-inch or bigger scope armed with a modern nebula filter.
The beauty of the apparently intertwining filaments as they spill out of the field of view defies description. Although you will never spot the fine-scale detail visible in photographs, there's something truly special about seeing the nebula with your own eyes. To get the most out of the view, be aware that OIII filters have a reflective coating that scatters light unless you've got it well shrouded. If you are holding the filter (as many observers do), cup your hands or use a dark hood to eliminate any interfering light.
The Veil Nebula represents the expanding remnant of a supernova that exploded some 30,000 years ago. This tenuous cloud has now broken into three primary sections that are quite a distance apart. The two outside arcs--NGC 6960 on the west and NGC 6992-95 on the east--appear brighter and contain the more impressive structures. Yet the middle part, known as Pickering's Triangle (NGC 6979), is quietly magnificent, thanks to its tangle of strands that taper into a long, graceful, S-shaped thread.
Martin Ratcliffe is former president of the International Planetarium Society. Alister Ling is a meteorologist with Environment Canada.