If we have sent you particular instructions for your instrumental configuration, forget this message or this text. If we have not given you specific instructions, these are the general instructions, organized by case.

A) If you observe with a telescope and the detector you have attached to the telescope is slow (like many amateur CCD cameras), the only way to obtain useful results is with the drift technique, also called "drift scan" in the that the telescope will take images of a duration longer than the occultation, say, 40s, with the telescope motors disconnected, so that Betelgeuse leaves a trace. Use an R, or V, or B filter, in this order of preference. It is not essential that they be photometric filters. Color R,G,B filters are valid. Check that there is no saturation. If there is saturation, use an even narrower filter. The SII, OIII and Halfa filters can be used, in that order of preference. If you do not have a filter, you can make a homemade filter to put in front of the telescope with red cellophane paper or similar, or red tinted glass. If there is still saturation, use a mask with holes to partially cover the telescope optics. That mask can be made with black construction paper or cardboard. The holes have to be everywhere. It is not worth making a single small hole because you would ruin the observation due to atmospheric scintillation (see notes). Another alternative is to try to get a cheap and simple video camera to attach to your telescope. Because of the star's brightness, even webcams would be useful, as long as you can attach them to your telescope. Another option is to try attaching a mobile phone camera behind the eyepiece of your telescope. See option C.

B) If you observe with a telescope and have a fast camera (type CMOS, or ccd video), this configuration is ideal. Try to get as many images per second as possible, but make sure you DO NOT HAVE DEAD TIMES OR TIMES IN WHICH THE DETECTOR IS NOT RECEIVING LIGHT: If you get 20 images per second, the integration time should be 0.05s, not less. If you get 50 images per second, the integration time should be 0.02s (no less), if you get 400 images per second, the integration time should be 0.0025s, no less. If you can take a detector window or ROI to improve the frame rate, do it. Use an R, or V, or B filter, in this order of preference. It is not essential that they be photometric filters. Color R,G,B filters are valid. CHECK THAT THERE IS NO SATURATION. If it saturates, you will have to blur, or put a narrower filter, but do not lower the integration time below the figure corresponding to your frame rate per second to avoid saturation! The SII, OIII and Halfa filters can be used, in that order of preference. If you do not have a filter, you can make a homemade filter to put in front of the telescope with red cellophane paper or similar, or red tinted glass. If you cannot defocus or do not have a suitable filter and the star continues to saturate, you can put a mask with holes in front of the telescope objective. That mask can be made with black construction paper or cardboard. The holes have to be everywhere. It is not worth making a single small hole because you would ruin the observation due to atmospheric scintillation (see notes).

The ideal observation should be with a monochrome camera with an R, V, B filter, in this order of preference. But if your camera is color, don't stop using it. The three color channels can be analyzed independently. In fact, in some respects the use of fast color cameras could be quite advantageous.

Use the free sharpcap software to record image sequences (or videos in .ser format, although we prefer fits image sequences).

C) You have a telescope, but you don't have a camera with which to record. In that case you can try to attach a webcam that you have to the eyepiece holder of your telescope, or cheap and light planetary cameras that already fit directly into the eyepiece holder (there are some for 60 euros or thereabouts, on the internet and in specialized stores, but it may be difficult get them in time) or attach the camera of your mobile phone to the eyepiece of the telescope. There are specific adapters for this, for just over 10 euros. This for example.  The main problem in these cases is that we do not know what integration times some of these cameras will use, because often these manual adjustments do not can be done in many of these cameras. For this reason, docking a mobile phone is the option that we least recommend.

D) If you observe with a telescope and have several cameras to choose from, use the one that gives the highest rate of images per second WITHOUT DEAD TIMES. See section B.

GENERAL NOTES

Don't get obsessed with having reference stars. See one of the notes below regarding if there are clouds, what to do.

Try to observe from the same place with two different instruments: 1) Video with a digital camera with a tripod, or mobile phone with a tripod, or mobile phone attached to a binocular and 2) observation with a telescope. The priority should always go to telescope observation.

It is important to observe with telescopes and the larger the diameter of the telescope, the better, because the noise due to atmospheric scintillation depends greatly on the diameter of the instrument used to observe. If small lenses are used, there will be a lot of scintillation (this is the reason why stars twinkle when we see them with the naked eye, because the size of our Iris is small and therefore the scintillation is large).

There is no need to go to the outskirts or to the countryside. It can be observed from cities or towns, even from windows that are properly oriented. In fact, this may be advisable to have easy access to electricity, computer and broadband internet.

The telescope does not need to be motorized and track.

If it is cloudy, but not completely, what to do? It is possible that it is cloudy with high clouds and Betelgeuse is detectable with a telescope although not with the naked eye or with simple means. Under these conditions, telescope observation may be simpler because the problem of saturation due to the excessive brightness of Betelgeuse will decrease, so it may even be useful, but it is convenient for another telescope in the same location to observe a very close star to try to compensate for variations in atmospheric transparency due to the passage of clouds. If you see that there are going to be clouds, try to coordinate with another known observer so that you are together and can do this. And if there is no auxiliary telescope, observe anyway because if the variation in atmospheric transparency is smooth, it can be modeled a posteriori.

Record at least one minute before to one minute after. Those of you who use drift scan or the drift method probably won't be able to do this. Make sure you know exactly what time the occultation occurs at your location. This is known with a precision of less than 1s. You can see it by clicking on the map at the bottom of this page: https://lesia.obspm.fr/lucky-star/occ.php?p=131608

Check that there is enough disk space or memory on our device to record.

Write down the coordinates of the place from where you are observing, using the GPS of your mobile phones. And/or with an image from Google Maps or Google Earth.

Precise time synchronization: Synchronize your computers via NTP using the free programs Dimension4 or Meinberg  and/or use the occult flash tag mobile application, which triggers a mobile flash before and after occultation.

Observing the occultation of Betelgeuse is very different from the majority of stellar occultations to which we are accustomed, and, furthermore, the main interest is the study of Betelgeuse, so the observation strategy must be well designed and improvised as little as possible. possible. Furthermore, the star is so bright that it causes numerous problems. The great brightness makes it easy to observe with many means, but also causes difficulties. It is advisable to rehearse before observation.

Once the data has been taken, contact your local coordinator to send them the data by wetransfer or a similar online service.