Blackish-gray cloud band on Jupiter?

[Josh Wilson]

Last night during my Jupiter observing session I noticed a fairly medium sized cloud band just above the very center of Jupiter. The time was about 9:30 and rotated regularly with the rest of the cloud bands. Could someone please tell me the name of this could band if there is any special name for it? Much appreciated.

[Davidv]

John, not sure if you're referring to the belts in general which are the are North Equatorial and Temperate belts and South Equatorial and Temperate belts with Polar regions at the poles. Apologies if I'm pointing out something you already know and meant something else.

http://en.wikipedia.org/wiki/File:Jupiter_Belt_System.svg

Dave

[Cath]

Sounds like Jupiter has a spot of UK weather

[stephen_usher]

Last night during my Jupiter observing session I noticed a fairly medium sized cloud band just above the very center of Jupiter. The time was about 9:30 and rotated regularly with the rest of the cloud bands. Could someone please tell me the name of this could band if there is any special name for it? Much appreciated.

There are some dark clouds extending from the northern edge of the equatorial zone into the zone which in low resolution image will look rather like dark triangles. There's one in this image I got on Sunday evening. (Rubbish atmospheric stability here, hence the fuzziness even using a 30 frame per second frame rate during the capture.)

[JamesF]

There has been a narrow dark band that seems to come and go very close to the equator recently. There's a hint of it in the image above.

James

[Josh Wilson]

After doing a bit of research I seem to have nailed it down to a simple festoon. They actually are a dark blue color but with dark adapted eyes (which aren't always good at picking up color) seem to make festoons look black-gray color. Thanks for the comments though, guys. And thanks for that diagram David, it's very helpful at identifying what I'm seeing. And great image Stephen, your technique is perfect, all you need are some stable skies!

[michael.h.f.wilkinson]

I did spot some festoons last Sunday. The NEB seems to be quite strong this year as well.

[cotterless45]

The belts seem to be changing a lot this year. We've seen other spots and darker areas to the edge of the belts. The GRS has also gone very pale. In addition to the changing appearance of the thinner belts there have been rips and festoons, all of which adds so much to viewing this most extraordinary planet, With such a short rotation it's worth keep coming back over the course of an observing session,

Nick.

[Josh Wilson]

The GRS has also gone very pale.

Very true. I'm actually noticing it's harder to located even when it's at the central meridian and I'm using a blue filter. I've also read that it's shrinking!!! :eek:

[michael.h.f.wilkinson]

Very true. I'm actually noticing it's harder to located even when it's at the central meridian and I'm using a blue filter. I've also read that it's shrinking!!! :eek:

The size of the GRS is somewhat variable. Sometimes a baby red spot appears (as it has this year), which is often swallowed by the GRS, after a while, causing the GRS to increase again. I have heard that given the size of the scope used for its discovery, the GRS must have been bigger at that time.

[Josh Wilson]

I have heard that given the size of the scope used for its discovery, the GRS must have been bigger at that time.

I'm not sure how this works... how could the size of scope used affect the apparent size of the GRS? Please explain. Much appreciated.

[michael.h.f.wilkinson]

A scope that size could not spot the GRS today, suggesting it must have bigger in those days.

[chiltonstar]

A scope that size could not spot the GRS today, suggesting it must have bigger in those days.

Asasuming that the discovery by Cassini was correct, do we know what aperture scope he used? After all, even a humble 80mm frac will show the GRS well today, and I imagine that Cassini used something rather bigger.....??

Isn't the optical performance/contrast more likely to be the main factor? Flare and CA would be a problem with a refractor with a simple (one element) lens of that era, and that would have prevented seeing today's anaemic GRS.

Chris

[JamesF]

I'm not sure how this works... how could the size of scope used affect the apparent size of the GRS? Please explain. Much appreciated.

The maximum resolution of a scope is related to its aperture and the image scale to its focal length, so if it isn't possible to see now something that it used to be possible to see with a scope with similar optical properties in the past then the assumption is that it must be more difficult to see now, ie. smaller.

As Chris points out though the build quality is probably also a factor.

James

[michael.h.f.wilkinson]

Asasuming that the discovery by Cassini was correct, do we know what aperture scope he used? After all, even a humble 80mm frac will show the GRS well today, and I imagine that Cassini used something rather bigger.....??

Isn't the optical performance/contrast more likely to be the main factor? Flare and CA would be a problem with a refractor with a simple (one element) lens of that era, and that would have prevented seeing today's anaemic GRS.

Chris

Contrast will have been a factor. At high enough contrast an unresolved structure is visible as a dot, the diameter of which is just the diffraction-disc size (e.g. stars ).

[Matsenator]

I saw the narrow dark band's my self the other day!

[Josh Wilson]

Ahhh... I understand now. If the scope was smaller and bad quality then this would make the disc harder to resolve. But if the GRS was bigger then, it would have been easier to see even if the scope was bad quality.

There is little evidence showing who discovered the GRS and it occured sometime between 1600 and 1800. Even then telescopes were in their infancy and optical quality was not at its greatest. It could have been bigger as well though...

[chiltonstar]

There is little evidence showing who discovered the GRS and it occured sometime between 1600 and 1800. Even then telescopes were in their infancy and optical quality was not at its greatest. It could have been bigger as well though...

It was certainly a lot darker and easier to see even a few years ago. As a kid I made a 2" refractor with a simple lens of 1m focal length and a microscope cheapo eyepiece - you could certainly see the GRS with that. If the GRS was around in Cassini's time, I'm sure he would have seen it if he could see the division in Saturn's rings bearing his name!

Chris

[michael.h.f.wilkinson]

I feel the GRS is very variable. Some periods it is quite dark, other times it is pale salmon in appearance.

[Josh Wilson]

I feel the GRS is very variable. Some periods it is quite dark, other times it is pale salmon in appearance.

It could very well be variable depending on wind speed, concentration of molecules, maybe even amount of sunlight it gets. According to Wikipedia: "Mathematical models suggest that the storm is stable and may be a permanent feature of the planet."

This doesn't say that the storm will get bigger or smaller in its lifetime, but rather that it'll be there permanently.

Also directly after that: "The storm is large enough to be visible through Earth-based telescopes with an aperture of 12 cm or larger."

This suggests that it was discovered when either larger aperture mirrors/lenses were fabricable or when high quality mirrors/lenses were fabricable. There is an ongoing debate between whom discovered the GRS but more credit is given to Giovanni Cassini for being the first to observe Saturn's moons.

Josh

[chiltonstar]

Certainly a nice GRS transit tonight for anyone out there (22:11) - tack sharp in my smallest scope (ED80) at x150 with the added bonus of a nice transit of Ganymede and its shadow, to say nothing of the nearby Moon!

Chris