Red Spot, Stellarium, and Starry Night

[George Jones]

Sky & Telescope gives times tonight for the beginning and end a transit of Io, and for when the Red Spot should transit Jupiter's central meridian,

SkyandTelescope.com - This Week's Sky at a Glance.

Stellarium (with "Simulate light speed" checked) and Starry Night agree with the times for the beginning and end of Io's transit, but, at the time given by Sky & Telescope for the Red Spot transiting the central meridian, both Stellarium and Starry Night show the Red Spot rotated past the central meridian and almost to the limb of Jupiter.

Is it just coincidence that Stellarium and Starry Night give the same wrong position for the Red Spot?

[daz]

Did you have Stellarium / SN time zone set correctly? The ST article is Eastern Daylight Time

[TheThing]

S&T does adjust the time in line with your computer's clock, if that helps. Stellarium and SN probably give the time in UT (aka GMT).

[David Galvin]

This S&T page gives the transit times of the GRS in U.T and you can use it to compare the times against SN and Stellarium. If the event times do not agree then maybe you will have to find where to enter, in your software, the curent position of the GRS. It is at longitude 138° in Sysem II

[George Jones]

Thanks for the replies, but I do not think that this is a time zone mix-up. I gave a link to printed EDT times, not to the Red Spot calculator, and I did not use the Red Spot calculator. My time zone is Atlantic Time, and AT = ET + 1. According to the printed S&T times to which I linked:

Io's transit started at 20:45 EDT = 21:45 EDT;

the Red Spot was on the central meridian at 21:39 EDT = 22:39 EDT.

According to the printed S&T times for Sept. 26 and independent of time zone, Io's transit started 56 minutes before the Red Spot reached the central meridian.

I have included a Stellarium screen shot for 21:45 ADT last night. No directions are reversed, so both Io and the Red Spot move from left to right. According to Stellarium, Io is just staring its transit, but the Red Spot is already past the central meridian, i.e., Io's transit stated after the Red Spot reached the central meridian. This disagrees with the printed S&T times for Sept. 26.

[bus_ter]

I know this is an old thread but I thought I would update it with an answer to help others who find it from a search result.

The GRS like a weather pattern is unpredictable and so the software must be updated every so often (annoyingly none of the software packages do this as part of their updates)

The latest position for the GRS can be found here: http://tinyurl.com/jupitergrs

As of Oct 2010 the value is 157

For Starry Night edit this file: \Starry Night\Sky Data\JupiterGRS.txt

For Stellarium update: \Stellarium\data\ssystem.ini ('rot_rotation_offset = 157') -This figure can depend on other settings just as 'simulate light speed'

EDIT: Apparently Stellarium doesn't take the Longitude position as the value, instead try a value of 120.

Hope this helps someone :-)

[George Jones]

Thanks for this. I have yet to try it, but I will.

[chiltonstar]

I have the same problem with Stellarium, ie GRS incorrect.

When I try to edit the ssystem.ini file (see above), it won't let me save the change - access denied comes up.

Any ideas?

Chris

[adamh]

Chris,

I'm guessing Windows 7 here (or possibly vista). In windows explorer right click the ini file, and choose properties. Go to the security tab, and click on "Users (YourMachineName\Users)" in the list of names. In the bottom box it probably has ticks next to "Read & Execute" and "Read" only. Click Edit. Then select users from the list again, and now tick the "Modify" box at the bottom. Click OK x2.

Adam

[Daggerstab]

An alternative is to copy the ssystem.ini file to your user data directory and modify it. It will override the original in the installation directory.

On Vista, the path to the user data directory should be something like:

C:\Users\YOURUSERNAME\AppData\Roaming\Stellarium

(It should contain the active copy of Stellarium's configuration file - config.ini.)

Create a "data" directory inside it, and put the copy of the ssystem.ini file inside that directory.

[The Warthog]

There's an annoying glitch at present in the presentation of local time on the S&T GRS chart. The times after 1200 hr are given in 12 hour clock, but without a corresponding PM or AM. You have to interpolate this frm the UT time given in the left panel.

[chiltonstar]

Adam,

Thanks very much - it worked.

Chris