I work with a bunch of people who work hard and depend heavily on humor to get them through the day. A couple weeks back someone bought donuts and set it out on the “wall of sharing” for the staff to enjoy. I grabbed one of the donuts early on. Later, after a long day, one last lonesome donut remained in the box. I passed it by once and considered taking it, but didn’t because, well, two donuts in a day is overmuch. Still I was hungry. My colleagues noticed this and encouraged me to go for seconds, but I held off. About a half hour later I walked by the box again and saw that someone had put a name tag on it. When I started to laugh, one of the copy editors said: “Looks like that donut’s got your name on it.” After more laughter, I finally gave in.
Before the moon gets too fat – no, not from eating pastry – I thought it would be a good time to introduce you to the sky’s prettiest donut of all, the Ring Nebula in the constellation Lyra the Harp. Seeing it for the first time through a small or medium-sized telescope reminds many observers of a donut or smoke ring. Now that’s Lyra’s well up in the eastern sky by nightfall, the Ring Nebula or M57 is one of the brightest planetary nebulas for telescopic viewing. Easy to find, too.
Look a little more than a third the way up on the eastern sky around 10:30 p.m. at the end of twilight. The brightest star visible is the diamond-like Vega. It completely outshines the other handful stars that form the compact, parallelogram-shape lyre or harp.
Vega is part of the Summer Triangle of stars that are all visible in the east by 10:30-11 p.m. Once you find Vega, look to the right to pick out the harp. Point your telescope midway between the stars Gamma and Beta at the base of the harp to find the Ring Nebula (see map below).
Its round, misty appearance might make you think you’re looking at an out of focus star. The Ring belongs to a class of deep sky objects called planetary nebulas, so called because their small sizes and round shapes reminded early astronomers of planets.
Nowadays we know planetary nebulas are the expelled outer atmospheres of evolved stars. Big stars larger than about eight suns end their lives explosively as we saw in the case of the new supernova in the Whirlpool Galaxy. In a sun-sized star, the core heats up as the star evolves, causing its outer atmosphere to expand into a bloated envelope many times its original size. These big gas bags are called red giant stars.
Over time, intense heat and instabilities in the core cause the star to expel its atmosphere into space in the form of an expanding bubble. The dying core, now called a white dwarf, emits intense ultraviolet radiation that illuminates the former atmosphere in shades of pale green and red. This is what happened to the Ring’s Nebula star. Photos show the white dwarf as a pinpoint of light at the very center of the ring. At its current expansion rate, astronomers estimate the age of the nebula at 6,000 to 8,000 years.
Because of perspective, it turns out that our view of the Ring Nebula is similar to looking down a barrel. The “hollow” center of the cylinder is the donut hole, while the ring shape is created by the stacking up of nebulosity as we peer the long way through cylinder’s walls. Pretty cool, eh?
Recent images taken by the Spitzer Space Telescope in infrared light show the Ring as more of a flower. Here we see older, fainter loops of hydrogen gas that were expelled long before the brighter ring formed.
No matter how you look at it,Â if you have a telescope, the Ring is a donut with your name on it the next clear night. Give it a view and let us know your impressions of this famous object.
Just to update you on supernova 2011dh in the Whirlpool Galaxy (M51), it’s still rather faint at magnitude 14.0, but that’s a little brighter than a few days ago. If you manage to spy it in a telescope, consider that hydrogen gas from the explosion is rushing your way at 11,000 miles per second. Astronomers at the University of California-Berkeley have identified the likely progenitor star as a yellow super giant with a mass 18-24 times that of the sun.
It also happened that the first person to notice the supernova was French amateur AmÃ©dÃ©e Riou on May 31. Independent discoveries came fromÂ StÃ©phane Lamotte (France), Tom Reiland (USA) and Thomas Griga (Germany).