Occultation by Nyanza on President Day across the US

Hello,

If you have an eVscope and you want to participate to a scientific campaign on Presidents’ Day, this is something that may interest you. The asteroid 1356 Nyanza will occult a V-12.2 star for up to 6 seconds on February 17 at ~8pm PST and 11pm EST. Yes! This occultation will be visible across the US, from Redding, CA to Philadelphia, PA and Chicago, IL. If a large number of eVscope users observe this event, we will be able to derive the size, shape and eventual existence of moons around the asteroid. So don’t wait and take your eVscope out if you are located nearby the visibility path of the event!

Astronomers are very interested in the shape and the size of asteroids because this helps them understand how they formed. For instance, a few days ago, a group of astronomers revealed the first pictures of the asteroid Pallas, which is heavily cratered, suggesting that the 170-mile golf ball asteroid had a violent history.

Unfortunately, most main-belt objects are too small to be imaged directly using a telescope, even a 8m-class one in an ideal location like Chile or Hawaii. However, astronomers have discovered a trick that helps them measure the size of asteroids—one that relies on the fact that asteroids move with respect to stars and sometimes even occult a star. Because the orbits of several asteroids are well known, it’s possible to predict where and when such occultations can be seen—that is, where a shadow equal in size to the asteroid will move across the Earth (see the diagram below from IOTA). Observers located inside the shadow will see an event (or a drop in the brightness of the star).

Asteroid Occultation explained (credit: IOTA)

We have already used our eVscope to observe several occultations (e.g. Andromache, Pluto, Orus). The most recent one was done in California in collaboration with the NASA Lucy team and will help them to derive the size and shape of Leucus, a Trojan asteroid which is also a target of the mission.

Your mission on Feb 17 2020

We propose to observe an occultation by a dark asteroid named (1356) Nyanza, a relatively unknown main-belt asteroid discovered in 1935 by a South-African astronomer named Cyril Jackson. Using the Occult program, we found out that the asteroid will occult a 12.2-mag star located in the Cancer constellation and that this event will visible in a small 40km-wide path crossing the USA.

Predicted visibility path for the occultation by Nyanza on Feb 18 made by J. Desmars from Observatoire de Paris.

Josselin Desmars, astronomer at the Observatoire de Paris Meudon, ran his own calculations and confirmed the event and its location. The kmz file and the embedded version shown below gives the location of the event based on the most recent estimate of the asteroid’s orbit. Observers located on the red line will be able to detect a long duration occultation (up to 6 seconds). The further the observer is located from the red central line, the shorter the occultation will be. However, the asteroid’s orbit is not well known and is very likely that the occultation could happen anywhere between the grey lines.

[Embedded map to be included soon]

Consequently, if you live nearby this area and the weather is nice on the evening of February 17, take your eVscope out and join us!

Here are the predicted times of the event for several locations along the path of the occultation:

• Redding, CA 8:05 pm PST (04:05 UT)
• Logan, UT  9:04 pm MST (04:04 UT)
• Sioux City, IA 10:02 pm CST (04:02 UT)
• Chicago, IL  10:01 pm CST (04:01 UT)
• Youngtown, OH   11:00pm EST (04:00 UT)
• Philadelphia, PA 10:59pm EST (3:59 UT)

Instructions and more:

• It’s necessary for the eVscope to get an accurate estimate of the time of the event, therefore, find a place with LTE/4G/3G or a WiFi connection.
• Since the star is relatively faint (12.2 mag), you should find a relatively dark place, avoiding street lights, car lights and habitations. A dark park in the suburbs should be OK (Bortle Class 4 or better). Contact us if you want to discuss several location options.
• To make sure that there is enough space on your eVscope to collect data, download any previous data on your phone, then connect to your WiFi and upload it to our server. To do this, click on “User”, then after it loads, click on “DOWNLOAD DATA”. Wait for it to finish and you will not want to use your phone while this downloads. After it downloads to your phone, disconnect the phone from your eVscope, turn off the eVscope, and connect your phone to your home’s high-speed WiFi network. Now select “UPLOAD DATA”.
• Make sure to charge your eVscope so it has enough charge for the ~1 hour observation
• At least 30 min before the predicted time (see above), set up your eVscope. You should be able to see the see the Cancer constellation (almost at zenith towards the West).
• Before connecting your phone to your eVscope, check the accuracy of the time on your phone by visiting time.is.  Grab the screen and/or note the information provided by the website.

Captured screen of the information provided by time.is (here on an iPhone). On Android, the web site does not force the adjustment of the time.

• Turn on your eVscope, connect it to your phone.
• Remove the dust cap (doh!), do a rough focus by eye, and run the auto-alignment. When it is successful point to a bright star in the Cancer constellation (like Acubens) and focus using the Bahtinov mask.
• Now that your eVscope is ready to record data, you need to point it to the star. Go to “Science”, then “Asteroid Occultations”.
• Enter the RA and DEC of the star (RA is 8h 14m 26.13s and DEC is 29° 34m 49.26s). Double check your numbers and then hit GoTo

Selection of the FOV for the Science Occultation using the Unistellar App v0.9 from Franck Marchis on Vimeo.

• Once the telescope finds your target, look at the example FOV (field of view).  Can you find your target? This is where your pattern recognition skills come in to play. If you need to slightly center the star use the joystick until the target is centered like in the example.

Observation of the FOV including the predicted occulted star (blue circle). Observation taken by D. Peluso from Vallejo, CA under poor sky condition with an eVscope

• You are ready. Now you just need to be sure that you capture the occultation event.
• 2 min before the event timing indicated above (choose the location closest to you or contact us to find out the timing of the occultation), go back to the “Science” menu, then press “Asteroid occultation” and enter the parameters of the occultation.  Exposure time = 500 ms, gain = 50 and duration = 2min
• 1 min before the event, press “Launch” and don’t move for 2min (you can breathe, but avoid stepping around the eVscope to minimize vibrations and avoid knocking it off).

How to start the recording in Science Occultation Mode from Franck Marchis on Vimeo.

• When the wheel is done spinning, you are ready to take dark frame for calibration. Simply cap your eVscope, go back to the “Science” menu, then “Asteroid occultation” and check if the parameters of the occultation are still the same (Exposure time = 500 ms, gain = 50) but this time put a duration of 10s only. Press “Launch” and wait ~10s.
• You are almost done.
• Park your eVscope and pack it. You can celebrate since you are now an occultation chaser!
• Send us the data by downloading the data onto your phone, then connecting to your WiFi and uploading it to our server.

This is a time critical event, so if you have time, I recommend you practice the day before. It will allow you to be sure that you know how to quickly set up, align, focus the eVscope, but also enter the coordinates in the menu (this can be tricky). Again, time accuracy is critical for these types of observations, so make sure you know how to use the time.is website and that you have found the right spot for your observation.

Keep in mind that this is a pilot program. We will improve the app so most of the operations described above can be done automatically. There is an average of 5-10 occultations per month and per location (in an 100 km radius area), so we will probably organize more of these events in the future!

Contact us by email at citizenscience@unistellaroptics.com if you have any questions and to let us know that you observed.

Interactive Map