The Great Red Spot

[Jimtheslim]

Apologies if this has been asked before, I have had a check of the forums but couldn't find it. I know Jodrell Bank has a list of dates to see the GRS on Jupiter, just wondering if these are the only times you can see them, or are they just the best times/dates? Is the appearance of the spot as regular to predict as the transits of it's moons etc?

[Stu]

I've not seen the Jodrell Bank data, can you post a link?

I imagine that it includes all visible transit but can check.

The GRS is a weather system so it changes frequently. It drifts around on the surface to a degree, so I believe it will be difficult to exactly predict the times far in advance, although I'm sure the estimates will be reasonably close.

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[John]

The Sky & Telescope magazine has an applet on it's website that predicts when the GRS will be on the central meridian of the planet. It's proved pretty accurate when I've used it. You need to register with website to use the applet but that is free.

[Jimtheslim]

This was the link I used. I'm sure I saw it somewhere on here but have since not been able to find the post.

http://www.jb.man.ac.uk/astronomy/nightsky/

Just wondered how they might be able to forecast its viewing with such seemingly precise times and therefore if it would not be so visible at other times. One day I'll see it!

[Stu]

I normally use the JupiterMoons app, which is driven off the S&T site. This is also very accurate and I believe the GRS position must be updated on a regular basis.

The only other area of error is in light transit time. Jupiter is around 35 or 40 light minutes from Earth, some apps need to be set to show things as we see them here rather than when they actually happen.

If it helps, there's one at about 00.50 on Saturday morning, then again at 20.50 ish on Saturday evening. Next one is then around 22.15 on Monday. They are roughly every 10 hours but obviously quite a few fall during daylight hours or when Jupiter is not visible

[Piero]

Just wondered how they might be able to forecast its viewing with such seemingly precise times and therefore if it would not be so visible at other times. One day I'll see it!

I believe they use mathematical models. It is possible to collect a lot of data on Jupiter (e.g. bands and zones rotation direction and rate, temperature, plus history of the planet events). You can fit the model parameters to such a data set and your model can then be used as a predictor. 

If your data set is sufficiently accurate and covers all the parameters of your model, your model can become a very accurate predictor too. I made some of them myself (although not for astronomy), and I can assure you that they work nicely and be very powerful. 

[Jimtheslim]

I see. Thanks for the heads up, but looks like cloudy skies for the next week or so. I observed Jupiter the other day at twilight and had the clearest, least aberration affected views I've ever had of the planet. Might do it more often.

[mikeDnight]

I have to admit I'm a bit lazy and don't check what's on view as I should. Yesterday while still daylight I took a look at Jupiter and the GRS was visible. The seeing wasn't too good due to turbulence, but I made a quick sketch anyway as it just helps me to concentrate. Attached is my daylight doodle.

Mike :-)