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銥閃 Iridium Flare 再過幾年就沒了--要看要快
據報導，銥衛星已由 Space X 部署第二代衛星，第一代衛星會逐漸淘汰，再過幾年就沒得看銥閃了。
Get Your Iridium Fix Before It’s Too Late!
The shock and dazzle of Iridium flares will soon be a thing of the past.
Here's how to make the most of seeing them before a new generation of spacecraft
replaces the Iridium satellites.
Each of the approximately 66 Iridiums in orbit have three door-sized
aluminum antennae treated with highly reflective, silver-coated Teflon for
temperature control.
When the angle between observer and satellite is just right, sunlight
reflecting off an antenna can cause the satellite to surge from invisibility up to
magnitude –8.5 in a matter of seconds. If you've never seen one, the searing
brilliance may make you recoil instinctively. On rare occasions, flares can
reach magnitude –9.5. That's 100 times brighter than Venus!
Sadly, that era will soon draw to a close. On January 14th, SpaceX’s
Falcon 9
delivered the first 10 of a new generation of Iridium NEXT satellites to
low-
Earth orbit, starting the process to replace the older units in a maneuver
called slot-swapping. While the new birds will provide faster data rates and
enhanced global communications, their antenna design is completely
different and not expected to produce significant flares.
Heavens Above is one of the easiest sites to get you looking in the
right place at the right time. The Heavens Above website allows for easy figuring and
finding of Iridium flares.
Just sign in and give it your location, then click the Iridium Flares
link under the Satellites heading on the left side of the homepage. A table will
pop open with a week's worth of passes that includes pertinent information like
brightness, altitude, and magnitude of the flare at flare center, the
brightest possible magnitude for a particular pass. Clicking on the date will
produce a map showing the flare's path and ground track where the flare will appear
brightest. When that path passes near or over your location, you'll see a –8
dazzler. If not, you can use the map to drive to the sweet spot and
await the display.
The transition to the Iridium NEXT generation will be gradual but
certain, so make the most of the opportunities that remain. If you're a teacher, do your
homework and plan an outing to show a daytime flare to your science class.
Anything that gets people talking more about the sky is a good thing, and I
guarantee those kids will never forget the sight.
[ANS thanks Bob King, and Sky and Telescope for the above information]
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