Well this week we find more and more meetings transitioning to online. We will comment on some ongoing classes and look at a tiny sunspot and return to our back of the envelope Stoke's Law analysis and how luckily the current COVID-19 is mostly not an airborne virus.
|Summer AAS 236th Meeting, scheduled for Madison, WI, now to be held online (Source: www.aas.org)
How are you doing in your selection of online astronomy related courses? I'm still trying to keep up in the general relativity course and just started the other Coursera course on the Solar System with Mike Brown at Caltech. He starts off easy enough, although some mathematics is coming later, with some historical accounts of Mars. So signup for free if you haven't already done so.
Here we see in this screenshot, two maps, the upper map drawn by Schiaparelli in 1888 and the lower map showing what can be seen by more current Earth bound telescopes. So we can see that some of the large features, like Hallas Basin, and mountains, seem to be accurate, but all the features interpreted as canals seem to be something different caused by observational effects of some kind.
|Mike Brown compares modern view of Mars to Schiaparelli's drawing from 1888 (Source: www.courera.org)
Hey, we checked in with our SOHO iPhone app and find that there is a tiny sunspot now. You can see it in the screenshot below. No, the sun is not green, but it just seemed the sunspot was easier to see on the enhanced image.
|There is a tiny sunspot visible now (Source: NASA/SDO as seen on SOHO app)
So, with a tiny sunspot available, I went outside with my flimsy tripod and 300 mm telephoto DSLR. Hmm, I hope this doesn't violate the shelter in place recommendations? No, of course not, nobody is out there! Anyway, with just a 300mm lens, I could not make out anything like the sunspot even with expanding the view. The identified sunspot is about 18" long and for my little Canon that is about 6 pixels. So, I suppose the data is there, but it's beyond my processing skills. At least the sun is waking up a little bit.
|Sun, as seen in actual frame size, 300 mm telephoto, DSLR, 1/125 second exposure (Source: Palmia Observatory)
In other news we saw that many of the Spring Breakers have now come down with the disease. When we were in Texas to view the SpaceX launch facilities the college crowd was just flying and we were luckily on our way back to OC. The social distancing recommendations only started to be applied a couple of days after we left our short visit to party central known as South Padre Island. Too bad for the sick students and we won't be travelling back to Texas for the upcoming Starship test launch either (and even later as reported by @BocaChicaGal, below).
|I remember that Spring Break like this might have been even more fun (Source: Business Insider)
Speaking of Starship launch and testing we just got a tweet from @BocaChicaGal that the SN3 failed the cryo-test of the fuel tanks. Check out these images showing first of all some venting and then of a piece of the tank assembly falling off and one final shot showing the ongoing failure. We will need to wait to hear what happened. Thanks for those photos, @BocaChicaGal!
|Cryo-testing of SN3 on the launch pad (with venting or failure?) (Source: @BocaChicaGal)
|Cryo-testing of SN3 on the launch pad (explosion?) with piece falling off (Source: @BocaChicaGal)
|Cryo-testing of SN3 on the launch pad (explosion?) after pieces fail and fall off (Source: @BocaChicaGal)
Finally, after seeing the SN3 test failure, we still need to return to our back of the envelope calculation efforts showing the effects of Stoke's Law, which describes how the size of the particle determines if the particle will remain in suspension in air or drop out due to gravity. We found that for very small particles, like in the size of virus particles, that they can remain suspended for a very long time. Will the actual viruses that are shed by infected people be in this size range? If so then we could easily get infected by just being in an elevator or in a carpool with an infected person. Luckily, it turns out that the sizes of particles and droplets that are actually expelled with breath or sneezing are much larger and will drop out much faster.
We hear the terms "Airborne" and "Airborne droplet" to describe the transmission mechanism for many viruses. These terms are a little confusing because obviously the virus travels through the air, but the difference in drop size is key. An airborne virus, like measles, can infect others over greater distances because the expelled virus is found in very small droplets. Other viruses like influenza are expelled in bigger droplets and will drop out of the air much more quickly. Why do different respiratory viruses cause different sizes of expelled particles? We see that a key parameter of the residence time of a virus is the actual particle size as expelled, not the actual size of the virus itself. This key piece of information is key to being able to use Stoke's Law to predict how long the virus will remain suspended in the air. Check out the table of actual transmission characteristics from the 8th edition of the textbook, "Introduction to Epidemiology."
|Transmission mechanisms for common viruses (Source: Ray Merrill, "Introduction to Epidemiology", 8th edition)
So, now the main question we are left with is the actual size of the expelled COVID-19 particles? Luckily, it seems that the virus is not "airborne" but is again, luckily, "airborne droplets." So, now we can leave the world of Stoke's Law behind and look at some recent announcements regarding this good news. This article from StatNews of March 16 shows the good news.
|Summary paragraph (Source: Sharon Begley, Statnews, March 16 2020)
For corroboration of that news article we can also go to the World Health Organization (WHO) and ask the question "Is COVID-19 airborne?" Well, no it seems not. Great! I have also read other news articles that say when the air quality of confined treatment spaces is tested they don't find high levels of virus, unless you come into closer contact.
|WHO 's answer to (Source: www.who.int)
Until next time, here from our burrow, stay sane, stay safe,