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Fig. 9.1. An observing form used to make a full disk drawing of Jupiter and record intensity estimates and the transit times of features as they rotate past the central meridian. (Credit: the Association of Lunar and Planetary Observers).

he has always hesitated to embark upon the making of a drawing of Jupiter, unless there has been to hand a fairly recent series of latitude measurements that will ensure his placing at least the four main belts at there correct distances from the centre of the disk. Some draughtsmen have a personal tendency to place objects too far from the centre of a planet, others to concentrate them there; so it is wise to resort to any legitimate means of attaining reasonable accuracy [512]."


Fig. 9.2. The author at telescope during early evening, making a full disk drawing and recording transit timings. (Credit: John W. McAnally).

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I have often used an eyepiece with a graduated reticle pattern to measure the disk of Jupiter and note the placement of the belts in relation to the reticle pattern. To do this, first measure the planet from pole to pole, noting the number of graduations over that distance. Transfer this number of graduations onto one of the observing forms. Next, lightly sketch in the positions of the belts in relation to that reticle pattern. Finally, go back to the eyepiece with the observing form and make sure you are satisfied with your placement of the belts. This form can now serve as a master form to lightly sketch in the belts on future observing forms. Usually, these measurements are good for several months. The measurement of the planet with the reticle pattern eyepiece can be performed several times during the apparition. Once the belts have been accurately placed on the form, other large features should be sketched in relation to each other. The shadings of these features, dark and light, can be partially completed.

Next, smaller features that can be seen should be drawn in relation to the positions of the larger features. By this time, you should be nearing the end of the 20-min period. During the time spent so far, you may have viewed through red, green, and blue filters.

Finally, more detail of all features already drawn can be added, including an accurate representation of the darkness or brightness of the feature.

In the remaining couple of minutes, compare the drawing to the telescope view making sure the drawing is accurate. Make note of the ending time of the drawing in universal time. Recording this time is very important.

Now, you can relax and record the other data needed for the observation (Fig. 9.3). Every drawing must record some standard information about the observation you made. For example, the A.L.P.O. observing form records the following information:

1. The name of the observer.

2. The location the observation was made from and the address (contact information) of the observer.

3. The date and time of the observation in Universal Time. Because your data may be of interest to astronomers all over the world, it is important to record this date and time in a manner that will not be confusing since people from different countries record dates in different formats. So, I always spell out the month, etc., like this: 2004August05/12:15 U.T. Remember that the date must also conform to universal time.

4. The type of telescope and its aperture.

5. The magnifications used during the observation.

6. Filters used, if any.

7. The seeing and transparency.

8. The beginning and end time of the observation in universal time.

9. The longitude of the planet's central meridian at the end of the observation/ drawing.

10. And space to record other information about observing conditions such as the presence of haze, wind, intermittent clouds, and any other descriptive information the observer feels may be necessary to help the reader fully understand the observation/drawing.

To the beginner this probably seems like an enormous amount of data to record for a drawing that was completed in just 20 min. But the truth is, without this information the drawing you just made is almost worthless. Next to the accuracy of your drawing, this information is the most important part of the observation. It allows the observation to become part of the historical record of Jupiter, and it allows other scientists to evaluate the data for themselves, a very important part of the scientific method. It also allows others to form an opinion about the credibility of the observation. An observation made under favorable conditions with adequate equipment is certainly more believable than one made under impossible conditions with a telescope that is too small to reveal the features recorded. So by all means, record the required information for your observation so that others will be able to rely upon your work.

As we will see, regardless of the type of observation or imaging you perform this information will be required of you.

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