Astro Bob blog: What's up, dock?Exactly how does the shuttle hook up with the space station while hurling around the Earth at 17,000 mph? Plus starry sights in the northern sky including a nice comet for telescope users.
By: Bob King, Duluth News Tribune
What's up, dock?
This Friday photo shows the space shuttle Atlantis' cargo bay and its vertical stabilizer intersecting Earth's horizon. Credit: NASA
All is well 217 miles overhead. Looks like the space station didn't need to maneuver around a piece of space junk. Updated tracking information showed it would miss the debris by a safe margin. The shuttle Atlantis was expected to dock with the station at 9:27 a.m. CDT today.
Ever wonder how two spacecraft manage to meet while traveling at 17,000 mph? After launch the shuttle is intially in a lower orbit than the station meaning it circles around the Earth more quickly. Let's say that Atlantis takes 85 minutes to complete an orbit and the station 90 minutes, and they're on opposite sides of the planet. Every orbit, Atlantis gains five minutes on the ISS. After so many orbits, the shuttle will now be considerably closer to the station. At the same time as Atlantis closes in, its orbital altitude is raised causing its rate of approach to slow. Astronauts using gravity like the breaks on your car -- by increasing Atlantis' elevation they increase it distance from Earth thereby enlarging its orbit and lowering its speed.
GPS satellites orbit 12,550 miles high and complete one revolution around the Earth in about 12 hours. Compare that to the space station at 217 miles and just 90 minutes. Once Atlantis is in the same orbit as the station and only a few miles apart, final maneuvers are performed at gentle speeds to bring it into position for docking.
Drop a rock from the Big Dipper and it will pass near the North Star
and down through the W of Cassiopeia. Created with Stellarium
I encourage you to face or walk north at night in the next few weeks to see a very cool lineup of stars and constellations. Go out around 10-10:30 p.m. and look high up in the northern sky. There you'll see the Big Dipper starting to topple over toward the west. If you imagine dropping a stone from the Dipper's Handle to the northern horizon, it will pass right through Polaris the North Star and on down through the W of Cassiopeia the Queen. If your skies are reasonably dark you may even find the queen's husband Cepheus the King below and right of the North Star. The star Gamma Cephei (SEPH-ee-eye), which is located one outstretched fist below Polaris, is one of the few easily visible naked eye stars orbited by an extrasolar planet. Called Gamma Cephei Ab and confirmed in 2002, it's at least 1.6 times the size of Jupiter.
This gorgeous photo of Comet C/2009 K5 shows a blue-green coma of gas and dust, bright central nucleus and faint tail. The color is from fluorescing carbon and cyanogen gas. It was taken May 13. Credit: Michael Jaeger
A fairly bright (8th magnitude) comet just happens to be cruising through the Norths Star's neighborhood over the next two weeks. If you have a 6-inch or larger telescope and dark skies, you'll see C/2009 K5 McNaught as a glowing ball of mist with a small, bright center. Larger telescopes show a faint westward-pointing tail. Comets always fascinate not only because of their mystery and beauty but they were likely the vehicles that delivered water to the early Earth.
Use this map to help you find the comet with your telescope. It spans about "one fist" of sky (10 degrees) from top to bottom and shows stars to 8th magnitude. K5's location is shown every two days. Tonight it's directly below the North Star. Created with Chris Marriott's SkyMap software