Todays pic is another one from onboard the International Space Station, yet another example of what isn't visible to those of us who are destined to stay earthbound for all of our days.
Mystery Meteors
They look like meteors flying in formation--three stars with stubby tails shining through Earth's airglow layer. Using a digital camera, ISS science officer Don Pettit caught them in a 15-second exposure on January 6, 2003. What are they?
The three stars of Orion's Belt.
NASA scientist Rob Suggs explains: "Orion was setting behind Earth's limb when Don took this picture. His camera was locked on Orion, so Earth's atmosphere moved upward during the exposure. As the Belt stars were covered, they were also deflected upward by atmospheric refraction--hence the illusion of three meteors in this long exposure. We know that the descent of the setting Sun is slowed by refraction; this is the same effect."
"The atmosphere acts like a giant lens," agrees expert Les Cowley. "Here on Earth, when we see the Sun setting with its center on the horizon, the uppermost limb of the Sun has, in fact, already just set. Refraction lifts the upper part of a low-hanging Sun by 0.25º --half its apparent diameter. From orbit, light rays enter Earth's atmosphere and then have an equally tortuous journey out again. Refraction is almost doubled. The setting Sun and setting stars are lifted twice as much."
Credit: Don Pettit, ISS Expedition 6 Science Officer, NASA
A larger versions of this pic can be found here, this is a 111K Jpeg image.
Previous Pic Of The Day posts
09th Apr 03
08th Apr 03
03rd Apr 03
30th Mar 03
28th Mar 03
26th Mar 03
22nd Mar 03
Mystery Meteors
They look like meteors flying in formation--three stars with stubby tails shining through Earth's airglow layer. Using a digital camera, ISS science officer Don Pettit caught them in a 15-second exposure on January 6, 2003. What are they?
The three stars of Orion's Belt.
NASA scientist Rob Suggs explains: "Orion was setting behind Earth's limb when Don took this picture. His camera was locked on Orion, so Earth's atmosphere moved upward during the exposure. As the Belt stars were covered, they were also deflected upward by atmospheric refraction--hence the illusion of three meteors in this long exposure. We know that the descent of the setting Sun is slowed by refraction; this is the same effect."
"The atmosphere acts like a giant lens," agrees expert Les Cowley. "Here on Earth, when we see the Sun setting with its center on the horizon, the uppermost limb of the Sun has, in fact, already just set. Refraction lifts the upper part of a low-hanging Sun by 0.25º --half its apparent diameter. From orbit, light rays enter Earth's atmosphere and then have an equally tortuous journey out again. Refraction is almost doubled. The setting Sun and setting stars are lifted twice as much."
Credit: Don Pettit, ISS Expedition 6 Science Officer, NASA
A larger versions of this pic can be found here, this is a 111K Jpeg image.
Previous Pic Of The Day posts
09th Apr 03
08th Apr 03
03rd Apr 03
30th Mar 03
28th Mar 03
26th Mar 03
22nd Mar 03
