Science desk
< October 21	<< Sep \| October \| Nov >>	October 23 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 22

Calculating the apparant location of the Moon(altitude/azimuth)

I'm writing a program to calculate the altitude and azimuth of the Moon as seen from a given location at a given time. I've translated the BASIC code on this page: http://www.stargazing.net/kepler/moon.html to Delphi. )I found an error or two.) I get it to agree with his sample of Birmingham, UK on August 9, 1998. His calculations agree with those of Mooncalc by Monzur Ahmed (given on that webpage).

However, he uses these figures for the latitude and longitude of Birmingham:

   lat : -1.91667
  long : 52.5

which are reversed. In his program glat and glong are used for the viewer's latitude and longtitude.

Question 1: are glat and glong reversed in his program?

Question 2: To convert from Right Assention and Declination to Altitude and Azimuth, it asks for the Hour Angle. Is that simply the number of degrees of longitude? Bubba73 ^{You talkin' to me?} 01:35, 22 October 2021 (UTC)[reply]

Well, I thought to put in the time of today's moonrise. With the lat and long as written, the data doesn't make sense. If I flip them, then I get 1.0 degrees altitude, 81.5 degrees azimuth for the time of today's moonrise, according to the weather report. Azumuth is 8.5 degrees north of east, which is reasonable. It gives the altutude at 1 degree, when it should be 0. His program is supposed to have a maximum error of 0.3 degrees. Bubba73 ^{You talkin' to me?} 02:29, 22 October 2021 (UTC)[reply]

Hour angle. Sagittarian Milky Way (talk) 03:59, 22 October 2021 (UTC)[reply]

The article says "... measured westward along the celestial equator from the meridian to the hour circle passing through a point." But the example the author gave, westward is negative. Is that inconsistent with the convention? Bubba73 ^{You talkin' to me?} 04:50, 22 October 2021 (UTC)[reply]

I have software where Earth's eastward rotation AKA the 1 westward spin of the celestial sphere per day adds to the hour angle, same direction as the article. The hour angle of the Sun is local actual (not mean) solar time in hours p.m (12 hours out-of-phase with 24-hour time, but the astronomical and nautical day are also 12 hours after or before the regular day), it would be weird if time counted down. Right ascension also ascends, not counts down (unless something is moving retrograde but retrograde orbits are cleaned from solar orbit in only millions of years so they're not that important). Sagittarian Milky Way (talk) 21:32, 22 October 2021 (UTC)[reply]

Webster's Dictionary also says westward Sagittarian Milky Way (talk) 13:56, 23 October 2021 (UTC)[reply]

I'm still struggling with that program. I worked on it most of the afternoon. I get my program to reproduce the output of the example given, but it is way off when I put in a different time and location. The program is a mess. He has lat and long backwards. A variable is missing a letter once, but that doesn't figure into the main calculations. He mixes degrees and radians - for instance a couple of things are in degrees but then they are converted to radians using the same variable. Bubba73 ^{You talkin' to me?} 22:44, 23 October 2021 (UTC)[reply]

I found an implementation of Jean Meeus' Astronomical Algorithms in C#, I cannot check cause I can only understand line number earliness-level BASIC (anything else hurts my eyeballs), but this C# alienese is likely far more well-written. You could also buy the book or an Explanatory Supplement to the Astronomical Almanac which is like a Farmers Almanac for astronomers, they've been making these for over a quarter millennium and the article says the Explanatory Supplement has more algorithms. Sagittarian Milky Way (talk) 06:12, 24 October 2021 (UTC)[reply]

Thanks, that sounds like what I need! I got the book Astronomical Algorithms by Meeus and I was reading the chapter on calculating the position of the Moon. But it is a little bit more like a course in the subject, making it hard to just read chapter 47 (Moon position) because it keeps referring back to things earlier in the book. But I'll get the program you found. Bubba73 ^{You talkin' to me?} 17:15, 24 October 2021 (UTC)[reply]

I downloaded the big file at that website, but I couldn't find the source code. But that said that it was based on programs by PJ Naughter, so I found http://www.naughter.com/aa.html and downloaded AA+ v.236 from there, and it has source code files I can read. IT is a big package of the programs. I was looking at the specific file for Moon position, and it is what I need. It looks like it depends on some other source files, but they look like they are all there. This is a side project for me, but I will get to it soon. Thanks! Bubba73 ^{You talkin' to me?} 17:43, 24 October 2021 (UTC)[reply]

Ah I didn't know Astronomical Algorithms chapters refer to other parts of the book a lot. Reading Jean Meeus' books is one of the many things I'll do as the number of realistic things I want to do but haven't done yet shrinks throughout life. Others include golf, ski, see an asteroid move with the naked eye, read encyclopedia articles I haven't gotten around to (like coelacanth) and if life is long enough I might have to start resorting to things like obscure sports and "read the entire Talmud". Sagittarian Milky Way (talk) 01:46, 25 October 2021 (UTC)[reply]

There are things like calculating the Julian date, etc. But the programs I found seem to follow the book closely, based on my brief examination. Bubba73 ^{You talkin' to me?} 02:14, 25 October 2021 (UTC)[reply]

Risk decrease of masks

When a COVID-19 patient (A) and an uninfected person (B) spend some time together, there is a certain risk of transmission. It may decrease if one or both wear surgical mask. The decrease can be expressed as a percentage. There are three situations: only A wears a mask, only B wears a mask, both A and B wear a mask. Article Face masks during the COVID-19 pandemic mentions percentages but does not distinguish situations. Has this been researched and percentage estimates published? Thank you. Hevesli (talk) 04:11, 22 October 2021 (UTC)[reply]

If anyone can answer that question with reliable information, it would be nice to add it to Face_masks_during_the_COVID-19_pandemic#Efficacy_studies_for_COVID-19. I cannot, so what follows is speculation.

I would assume no such research exists for covid19. A response study (asking A and/or B purposefully not to wear masks when it is known that A is probably infected) would be highly unethical with a disease that severe. I imagine it is hard to design a proper observational study (if you ask people who have been around sick people who wore masks when, the chance of lying/misremembering is fairly high). This being said, such studies might have been done for other diseases that could be used as models of transmission (e.g. common cold coronavirii). Tigraan^{Click here for my talk page ("private" contact)} 09:40, 22 October 2021 (UTC)[reply]

An evidence review of face masks against COVID-19 (Jan 2021) says:

Cochrane [1] and the World Health Organization both point out that, for population health measures, we should not generally expect to be able to find controlled trials, due to logistical and ethical reasons, and should therefore instead seek a wider evidence base. This issue has been identified for studying community use of masks for COVID-19 in particular. Therefore, we should not be surprised to find that there is no RCT for the impact of masks on community transmission of any respiratory infection in a pandemic.

Alansplodge (talk) 10:26, 22 October 2021 (UTC)[reply]

Just as an aside: this year's (2021) Prize in Economic Sciences (commonly called the Nobel Prize for Economics) was awarded to laureates who showed how to use "situations in which chance events or policy changes result in groups of people being treated differently, in a way that resembles clinical trials in medicine"; the prize was specifically awarded for solving "this methodological problem, demonstrating how precise conclusions about cause and effect can be drawn from natural experiments." In other words, when it is not possible or ethical to conduct a proper random control trial, there is still a valid methodology to draw conclusions with equal scientific rigor. It happens that this methodology is "difficult," which is why the prize was awarded to a few scientists who "totally revolutionised the way we do empirical work."

Guido Imbens even wrote an entire book titled Causal Inference for Statistics, Social, and Biomedical Sciences. The book offers "unprecedented guidance for designing research on causal relationships, and for interpreting the results of that research appropriately." This sounds verbose, but I would endorse it. We don't want a simple "yes" or "no" on whether masks decrease the risk of transmission: we need a nuanced and careful methodological approach to this question. It is this nuance - particularly, distinguishing scientific methodology from hollow weasel-wording - that I believe justifies the award; and, simultaneously, is what implies that you need a book-length answer to a question that initially sounds like it deserves a simple binary-answer.

Nimur (talk) 17:43, 22 October 2021 (UTC)[reply]

There was a widely covered Bangladesh study a few months ago touted as the first real-world test of masks. Note also the study showing Delta to be 42 times more prevalent in aerosols than Alpha. And a study this month showed TB to be an airborne disease as well. In many ways, the medical authorities have yet to catch up to the dangers of aerosols. Imagine Reason (talk) 01:49, 24 October 2021 (UTC)[reply]

Tuberculosis is different, being "airborne", it can circulate in the air for extended periods and infect at longer distance. Coronaviruses are understood to remain in suspension for relatively short periods. That said, other factors that increase complexity are exposition time (an hour at 2m is not considered to be the same as 15 minutes or less and is taken in consideration in some tracing models), distance (the droplets tend to disperse and fall), lung capacity and symptoms (loud singing or a powerful sneeze can project considerably beyond distancing guidelines), but masks do mitigate droplets aerosol to some extent... —Paleo Neonate – 22:05, 28 October 2021 (UTC)[reply]