19 Mar 2012
A few weeks back we took a look at satellites. This time we look specifically at one type of satellite which has a unique characteristic with which to wow your family and friends.
The Iridium satellites are a "constellation" of dozens of communication satellites put in orbit by Iridium Communications, Inc. Not a big deal so far except that there is a part of each satellite which is highly reflective. On each are three very shiny antennae which, when the satellite is arranged just perfectly, can reflect sunlight with a vengeance.
Most of us who have seen satellites know they are not too much brighter than most of the stars up there. But the Iridium species can reflect so much light that they can register a magnitude -8. For the uninitiated, that is about 40 times brighter than Venus, that bright planet setting in the west after sundown.
Because they have to reflect at just the precise angle to the sun, they essentially appear and disappear within just a handful of seconds. But the fun thing is that you can predict exactly when and where in the sky this happens. And when it does happen on cue, it is a pretty cool sight to behold. Ready to try?
First you will need the coordinates of where you are. For the sake of example, let us assume you are at home. You can find your exact latitude and longitude many ways, but if you have access to the internet, you can just go to a site like iTouchMap.com.
Along their top menu, you will see a selection called Lat-Long. Go to that page, enter your address, and write down the coordinates they give you.
Now go to heavens-above.com. Under Configuration go to the Edit Manually link. There enter your latitude and longitude and your time zone - all critical information. Submit that.
You are taken back to the main page. Under Satellites see Iridium Flares. Click "next 7 days." There you will see listed the dates and times for upcoming flares. Pick one with a low magnitude (remember the lower the magnitude, the brighter).
On that date and that exact time, look up in the sky at that angle above horizon (altitude) and in that compass direction (azimuth) and before your very eyes a point in the sky will flash in extraordinary brilliance.
This all can seem a little complicated at first, but can get very easy, very quickly. Then you can show friends and family. Or you can use it in situations like this with your spouse, "Dear, if a light appears in the sky right there in one minute, can I get the new iPad?" Or to your kids, "If there is a flash of light in the sky right there in 15 seconds, you will weed the entire backyard, OK?"
Want the lazy man way of doing it, like I do? Get Sputnik!, an app for the iPhone which automatically does all the above in seconds.
04 Mar 2012
In the sky this evening, after sunset in the west, are a couple of bright planets, Venus and Jupiter. The dimmer of the two, Jupiter, was visited by a workhorse spacecraft 33 years ago this day.
The spacecraft was one of a pair of big boys launched in 1977 called Voyager. Loaded with instruments for exploring the outer solar system, both Voyager I and II were launched in late summer of that year to take advantage of a special alignment of the outer giants. If launched on time and pointed in the right direction they could visit Jupiter, Saturn, Uranus, and Neptune - a virtual coup of 4 of the 5 outer planets all in one trip. (These were the days when Pluto was still considered a planet.)
Voyager II was actually launched ahead of Voyager I, in August 1977, with Voyager I launched just weeks later. But because of different trajectories, Voyager I was the faster of the two and arrived at Jupiter only a year-and-a-half later, with its closest approach coming on March 5, 1979.
Voyager II slow-poked it to Jupiter, arriving there in July, 1979. But even though Voyager I got bragging rights for getting to Jupiter and Saturn first, it was Voyager II's slower pace that allowed it to line itself up for its extended trip to Uranus and Neptune.
What did these two work horses accomplish? Well, besides taking stunning images, they sent back loads of information about all kinds of features on those planets.
The pair observed the moons of Jupiter, discovered volcanic activity on its moon Io, and found a nearly invisible ring around the great planet.
In 1980-81 they reached reached Saturn and of course studied in great detail the majestic rings there. But they also flew by several of the moons, including giant Titan, a satellite so large it has its own atmosphere.
It is here Voyager I ended its planetary tour – but Voyager II took a slight turn and trekked on. Passing by Uranus in January 1986, the spacecraft studied its featureless body, some of its moons, and the feint rings around the planet.
It then travelled on to the last planet on its tour, Neptune. There, in August of 1989, Voyager sent back images of crazy weather patterns, its mammoth moon, Triton, and the faintest rings imaginable.
Where are they now? They are still working! Voyager I is about 17 billion kilometers away and Voyager II is at about 14 billion. They are relaying information from the crazy world of the heliosphere, the farthest region of solar influence.
The Voyagers are a "living" tribute to their creators, the engineers at the Jet Propulsion Laboratory in Pasadena.