Starship Asterisk*

Io: Moon over Jupiter

Explanation: How big is Jupiter's moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the featured picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts Io nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. In July, NASA's Juno satellite began orbiting Jupiter and will sometimes swoop to within 5,000 kilometers of Jupiter's cloud tops.

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APOD Robot wrote:Although in the featured picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts Io nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon.

While this view exaggerates the perspective, it's still the case that from Io, Jupiter appears about 19° across, or 38 times larger in the Io sky than the Moon appears in ours. That's got to be pretty impressive!

Chris Peterson wrote:

APOD Robot wrote:Although in the featured picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts Io nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon.

While this view exaggerates the perspective, it's still the case that from Io, Jupiter appears about 19° across, or 38 times larger in the Io sky than the Moon appears in ours. That's got to be pretty impressive!

That's for sure. I used Stellarium to simulate a direct image comparison for the Earth-Moon. Cassini was about 9.6 million km from 1.3 arcminute Io; the Jupiter-Io image is ~20' square.
 

I believe Europeans usually pronounce Io "EE-oh," rather than "EYE-oh," but I'm not sure. When I was a kid I pronounced Orion "OR'-EE-ON," having never heard it said. EE-I-EE-I-OH !

heehaw wrote:I believe Europeans usually pronounce Io "EE-oh," rather than "EYE-oh," but I'm not sure. When I was a kid I pronounced Orion "OR'-EE-ON," having never heard it said. EE-I-EE-I-OH !

Quite naturally, as Io is named after a figure from greek mythology. Not sure, why apod tries to cement the mispronunciation.

guenther wrote:

heehaw wrote:I believe Europeans usually pronounce Io "EE-oh," rather than "EYE-oh," but I'm not sure. When I was a kid I pronounced Orion "OR'-EE-ON," having never heard it said. EE-I-EE-I-OH !

Quite naturally, as Io is named after a figure from greek mythology. Not sure, why apod tries to cement the mispronunciation. :roll:

Because the modern English pronunciation is EYE-oh. For both the moon and the mythological character. That's quite correct. We don't insist that words maintain their archaic pronunciations.

Chris Peterson wrote:We don't insist that words maintain their archaic pronunciations.

So, does that mean you agree that it is fine if we decide to start pronouncing your name as Car-Ice?

suicidejunkie wrote:

Chris Peterson wrote:We don't insist that words maintain their archaic pronunciations.

So, does that mean you agree that it is fine if we decide to start pronouncing your name as Car-Ice?

You're welcome to pronounce it any way you want. But if you expect me to respond, I'd suggest the conventional modern English pronunciation, not an archaic or foreign one.

Ok. Enough with the language lessons and implied insults, can I ask an astronomy question?

I know that Jupiter is big, really big. An that Io is the distance of the moon to the earth. But I'm looking at the photo and it seems as tho disturbances in the Jovian atmosphere are kind of in-line with the orbit of Io. Is there some sort of gravitational effect taking place to account for this; similar to tides on earth but with a lesser overall effect on Jupiter?

Guest wrote:Ok. Enough with the language lessons and implied insults, can I ask an astronomy question?

I know that Jupiter is big, really big. An that Io is the distance of the moon to the earth. But I'm looking at the photo and it seems as tho disturbances in the Jovian atmosphere are kind of in-line with the orbit of Io. Is there some sort of gravitational effect taking place to account for this; similar to tides on earth but with a lesser overall effect on Jupiter?

Not sure how you can tell from the picture the plane of Io's orbit. But it does, in fact, line up with the cloud belts. That's because most everything in the Jovian system is very close to Jupiter's equatorial plane (just like the planets are very close to the Sun's equatorial plane). This is most likely a consequence of the formation of these systems from coalescing discs of material. And the cloud belts on Jupiter are parallel to its spin axis- something that we see with all spinning bodies that have atmospheres.