Astronomy Picture of the Day 3-19-03

NASA ^ | 3-19-03 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2003 March 19

Jupiter's Great Dark Spot
Credit: Cassini Imaging Team, Cassini Project, NASA

Explanation: Seventeenth century astronomer Giovanni Domenico Cassini was an astute observer of Jupiter's Great Red Spot. So it seems only fitting that his namesake, the Cassini spacecraft, has enabled detailed observations of another planet-sized blemish -- Jupiter's Great Dark Spot. Unlike the Red Spot, the Great Dark Spot lies near Jupiter's north pole and seems to appear and disappear over periods of months rather than persisting for hundreds of years. Seen at ultraviolet wavelengths, the dark feature resides in the Jovian stratosphere confined by pole-encircling winds, analogous to planet Earth's antarctic ozone hole. This image of the Dark Spot is a single frame from a movie created with data recorded during the spacecraft's year 2000 flyby of Jupiter. Projected to show Jupiter's north polar region, no data is available for the blank central area, while the Great Dark Spot lies above and just left of center. The white circle marks 60 degrees latitude and the blue contour outlines a persistent Jovian auroral zone which may be related to the formation of the Great Dark Spot.

[petuniasevan]

That's a Dark Spot all right; I can't see anything but black there.

Wait a minute. My bad. THERE'S the Dark Spot, to the upper left of the polar region's dataless central region!

Here's the source movie as thumbnail; click on the image for the full-size GIF movie.

UV movie of polar Jupiter

WARNING! The full-size GIF is big! That's not so much in dimensions (512 square) but in file size. It's about 26 MB so slow Internet connections may be overwhelmed. It's worth a short wait for the great visual impact.

[petuniasevan]

[petuniasevan]

Off-topic here, but if when we go to war after today's deadline, I may have to curtail posting of this thread. Right now Jim is just restricting Breaking News to war-related topics, but there may be bandwidth issues or just plain overloaded servers as the fireworks start. If Jim asks, I will certainly put the APOD on temporary hold.

Also: I will be on vacation the first week of June (no, not FReeps Ahoy; visiting relatives in SoCal). If anyone would like to post APOD for a week (HTML skills a big plus for fixing intralinks), please let me know.

[GodBlessRonaldReagan]

Great pic! I will certainly miss APOD if it goes on hiatus for the war...

[mikrofon]

Darn, those lipstick marks don't seem to want to go away ;^)

Great catch, as always .... will also miss APOD, but if needs be, let's roll!

[RightWhale]

This spot is a migrating resonance in the jet stream. The jet stream is a kind of standing wave induced by the various atmospheric forces and insolation. The speed of moving air inside the jet stream is higher than the general atmospheric rotation, which is faster than the planetary rotation. Since the standing wave lacks perfect resonance around the planet, there is an instability, a partial resonant peak that continually migrates in search of the next higher resonant number. Thus, if the resonant wave has four peaks, the partial peak would be the fifth, except that it can't settle into one location since it is somewhat away from being in tune. Call it a wolf note or a discord in the jet stream.