Good and interesting article.  I can explain it in fewer words, though:

Twinkle, twinkle, little star
God made you the way you are.

JulieMelton
visit me at
www.heart-and-music.com
Keep smiling!


----- Original Message -----
From: "Phil Scovell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, December 23, 2005 6:37 PM
Subject: Twinkling Stars


> Since I brought up the question, how difficult is it for a star to
> twinkle,
> I thought the following short article might be of interest.
>
> Phil.
>
> Mystery of twinkling stars explained
> The University Record,
> February 7, 1994
>
> Mystery of twinkling stars explained
> The child's poem, "Twinkle, twinkle, little star," describes a familiar
> sight in the night sky, according to U-M astronomer Richard G. Teske.
>
> "During cold February nights, the twinkling of bright stars is especially
> striking; sometimes they seem to shatter into dazzling shards of blue,
> red,
> and
> green," Teske says. "While the vivid display delights most star watchers
> with its movement and color, the twinkling interferes with delicate
> observations
> made by astronomers."
>
> Twinkling of stars-called "scintillation" by astronomers-is caused by
> moving
> air currents in the atmosphere. The beam of light from a star passes
> through
> many regions of moving air while on its way to an observer's eye or
> telescope. Each atmospheric region distorts the light slightly for a
> fraction of a
> second.
>
> "The total result of a great number of momentary small distortions is the
> twinkling that we see," Teske explains. "Although these atmospheric
> motions
> are
> present all the time, they are especially noticeable on cold winter
> nights."
>
> Teske says that Michigan sky watchers can observe twinkling by watching
> February's stars between 7 and 8 p.m. on clear, crisp evenings. Sirius,
> the
> brightest
> star in Earth's sky, is low in the southeast, while the stars of Orion the
> Hunter hang higher in the south.
>
> Sirius is closer to the horizon than Orion, Teske explains, so its light
> passes through more air than the light from Orion's stars. Early in the
> evening,
> Sirius flickers more intensely than the stars of Orion. A few hours later,
> when Sirius is nearly directly south and its light comes through less of
> the
> atmosphere, its twinkling diminishes noticeably.
>
> "Anyone who uses a telescope is aware that scintillation causes images of
> stars to wobble and waver. The effect blurs and enlarges star images on
> photographs
> captured during astronomical time exposures," Teske notes. "If there was
> no
> atmosphere overhead, the photos would be much sharper. This is one of the
> reasons
> the Hubble Space Telescope was positioned high above the atmosphere-to
> achieve the extremely sharp pictures that can be taken when no air motions
> interfere."
>
> Ground-based astronomers have tried to get around the problem by putting
> telescopes on high mountains to get them above most of the atmosphere.
>
> One of the world's finest observing sites, Teske says, is nearly 14,000
> feet
> up on the extinct volcano Mauna Kea on the island of Hawaii. There,
> several
> huge modern telescopes take advantage of tranquil skies to image the
> heavens
> with a sharpness never achieved before the launch of the Hubble Space
> Telescope.
>
> "But the 14,000-foot altitude is about as high as most ordinary people can
> work comfortably for several hours at a time, and it is unlikely that
> large,
> manned observatories will be placed on taller peaks," Teske says.
>
> The future is coming into sharp focus. A telescope placed on Mauna Kea can
> just about distinguish George Washington's presence on a quarter from
> three
> miles
> away. Astronomers are hopeful that in the near future the same telescopes,
> when equipped with new devices to compensate for bad images, will come
> close
> to being able to distinguish his face from the same distance.
>
> "But even this will not surpass the performance of the newly refurbished
> Hubble Space Telescope," Teske says. "It will recognize-at three miles'
> distance-the
> ribbon that ties Washington's pigtail."
>
> End of article.
>