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The Timeline of Observations

In order to calculate the time line of observations, first we calculate, how far the point, where the intensity is half of the nominal stellar intensity, the I1/2 point, is away from the predicted time points, which are given here.

According to recent publications (E. Raynaud et al, Icarus 162 (2003) 344-361) the I1/2 point is about at an atmospheric pressure of around 2 ┬Ábar. Assuming an isothermal behaviour in this range of the atmosphere and a scale height of around 30km (same paper), the 1 bar pressure layer is around 13 to 14 scale heights away, which is equivalent to about 390 km. Just to remember, the scale height is the distance in an isothermal atmosphere, where the pressure is changed by a factor of e (=2.718).

Now the true velocity orthogonal to the Jovian limb has to be calculated.

The velocity of Jupiter with respect to an observer on Earth (calculated for Munich, Germany, using the JPL ephemeris system HORIZONS) is 16.68 km/sec. Now this value has to be projected orthogonal to the Jovian limb. The zenographic latitude of the point of contact is around 50 deg, which reduces the velocity orthogonal to the limb to

16.68 km/sec * cos(50┬░) = 10,7 km/sec.

This is the relevant speed, which has to be used in the calculations.

From the given contact times (valid for 1 bar pressure), the I1/2 point is 390km away or 36 seconds. If we take into account, that the start of the visible occultation is even earlier (from the paper above a minimum of around 50 seconds), possible begin of light dimming could occur around 100 seconds earlier as the 1 bar occultation timepoints.

Given for Munich (Germany, and this is true for nearly all cities in central Europe), the disappearance on the 1 bar level is around 22h 58 min UTC, starting from about 22h 56min UTC a first dimming could be observed.

Before the Disappearance, Keep in Mind...

Recording of the event should start a minimum of 60 minutes earlier (this is equivalent to a distance of about 15 arcsec), because for data analysis the stellar intensity of the star has to be recorded without any interference with the atmosphere, to give the level of light from the star separately from any disturbance by the bright Jovian limb. Better even: images long before, 1 hour or longer, elevation permitting, have to be taken to get this undisturbed intensity.

And recording the star close to the Jovian limb even before the occultation is important in order to model the separation of the stellar intensity from the Jovian bright disk. Without a careful recording, no analysis may be possible.

The same is valid after the event, so I feel the following procedure has to be applied:

Start recording images as soon as Jupiter is high enough in the sky, may be not continuously, but every 10 minutes for about 30 seconds.

At 15 minutes before the nominal 1 bar occultation time start recording with nominal speed.

After Disappearance and Before Reappearance

Now, if the air quality is very high and we are lucky, a flickering and short reappearances of the star could be observed over a long period (= a few minutes) after the 1 bar time point, in certain wavelengths even a continuous monitoring of the star during all the occultated period can be possible (in K-Band perhaps!). So, don't switch of the camera, and make sure, that you have enough disk space left in the computer.

The Reappearance

The same procedure should be done after the reappearance, taking images for about 15 minutes more, and test images for the next hour or longer,. Don't go to the champagne too early, or you may loose science.

Graphic representation

Here you find a graphic summary, what you should do as a MINIMUM! Keep in mind, taking more images is never a problem, but look, how much space you have on disk or tape!

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