Catch a high-speed star

Piazzi’s flying star

“I have seen the stars move.” Wouldn’t that be a cool statement to make? Even with a small telescope, you can witness stars moving. We’re not talking about the stars’ nightly, east-to-west motion caused by Earth’s rotation. Rather, we want to see stars move through space. If you choose a fast-moving star, you can detect its displacement relative to more-distant stars in less than a lifetime.

Stars close to Earth appear to move the fastest. Picture two planes: a high-flying jet and a nearby, remote-controlled model. Despite a much slower speed, the model whizzes past your head compared with the stately progress of the distant jet. In the same way, nearby objects offer the best targets for detecting movement. Although Barnard’s Star in Ophiuchus moves the fastest, 61 Cygni ranks among the top five.

BRIGHT PLANETARY NEBULA NGC 7027 looks rectangular through a small telescope, but you won’t see the detail the Hubble Space Telescope captured here.

With your naked eye, you can see 61 Cygni in the upper left of Cygnus the Swan. A nice surprise awaits you when you point a telescope at 61 Cygni. Not only does it split into a pair of stars, the two components glow with a light-orange hue. From their color and brightness, astronomers deduce these stars are smaller and fainter than the Sun.

The pair takes 653 years to complete one orbit. The stars currently appear 30" apart, a bit less than Jupiter’s apparent size. But at a distance of 11.4 light-years, this separation translates into a gap of about 100 astronomical units, or 2.5 times the Sun-Pluto distance.

In 1792 (9 years before he discovered the first asteroid, Ceres), Italian astronomer Giuseppe Piazzi noted 61 Cygni’s rapid motion. It moves 5" per year. So, in just 6 years, the pair will move an amount equal to the current space between them. Use as much magnification as the atmosphere and your telescope will allow, and make a sketch of the pair along with nearby stars. Put your finished drawing where you can’t lose it. Then, return to the field in 5 or 6 years to see if you notice a change.

EASTERN CYGNUS OFFERS OBSERVERS several worthwhile targets, including the rapidly moving double star 61 Cygni and the bright planetary nebula NGC 7027.

Two hundred years ago, no one knew how far away the stars lay. It wasn’t until 1838 that German astronomer Friedrich Bessel finally detected the tiny side-to-side annual wobble of 61 Cygni. This parallax gave Bessel the first rough measure of any star’s distance.

Bright blob

If you observe from the city, it helps to target objects with a high surface brightness because they punch through the sky-glow. Planetary nebulae are good choices. Although small, their light is concentrated. You can find 8.5-magnitude NGC 7027 a few fields north of 61 Cygni. Unlike the Ring (M57) or Helix (NGC 7293) nebulae, NGC 7027 appears nearly rectangular instead of circular.

A nebula of high-contrast filter will make NGC 7027 stand out from the background. But, as long as you magnify by at least 100x, you hardly need one. An 8-inch or bigger scope brings out the nebula’s green color, although some observers describe it as more blue.

Martin Ratcliffe