Wikipedia:Reference desk/Archives/Science/2021 July 24

= July 24 =

Submarine (anti) rainbow
Consider the usual model of a rainbow: What happens if we switch air and water? Namely, suppose the observer is under the water, surrounded by a cloud of small spherical gas bubbles, in a bright day. I imagine there can be refraction and light diffusion, maybe without reflection, so that a rainbow may be visible e.g. if the air bubbles are between the observer and the light source. But does something like that really occur? pm a 15:10, 24 July 2021 (UTC)


 * A water-filled sphere in air works like a convex lens: a bundle of parallel incident light rays is made to converge. The reflecting other side works like a concave mirror, also promoting convergence. The combined effect is shown in the first figure at . An air-filled sphere in water works like a concave lens, so entering incident parallel light rays are made to diverge. The equation for $$\beta_\operatorname{max}$$ in the next subsection for solving $$d\phi/d\beta=0$$ does not produce a real solution. Also without internal reflection, I think the doubly diverging rays (a second round of divergence occurs on exit) cannot be expected to produce striking visual effects.  --Lambiam 20:25, 26 July 2021 (UTC)

Why can't NASA ascertain about total number of artificial satellite payloads around Earth?
This line from here says: In 1997 NASA estimated there were approximately 2,465 artificial satellite payloads orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center. Why can't NASA easily add artificial satellite payloads if we have lists like this ? Rizosome (talk) 15:40, 24 July 2021 (UTC)


 * I do not understand why you think this incomplete list of communications satellite firsts can help NASA or anyone produce a list of all orbiting payloads. There is no easy way to tell if an orbiting object is a payload, artificial junk, or a (temporary) natural satellite, such as and .  --Lambiam 23:11, 24 July 2021 (UTC)


 * Some sources to contextualize the scale of the problem for the OP, though it should be noted that they are not generally concerned with just enumerating payload launches but rather discussing the issue of orbital debris tracking and management holistically:, , , , , , , . Snow let's rap 23:16, 24 July 2021 (UTC)

who buys all the 555?
It is said that over a billion are made every year, yet I've never ever seen a 555 "in the wild" and I've taken apart a thing or two. Aecho6Ee (talk) 17:34, 24 July 2021 (UTC)


 * They are not as common as they used to be, since it's often cheaper to do that stuff with digital parts now. The 555 is an analog timer that will often use a comparatively bulky external capacitor as part of an RC delay.  That stuff is relatively expensive compared to a 3 cent microprocessor or just putting a timing function into some microprocessor that is already part of your circuit.  2601:648:8202:350:0:0:0:2B99 (talk) 05:06, 25 July 2021 (UTC)


 * Keep in mind that you wouldn't necessarily recognize them. The through-hole version they sell for hobbyists and legacy devices are easily spotted, but you can get them in much smaller packages.
 * Check out this lineup. The one on the left is a traditional looking 555, and the one on the far right looks like it could be accidentally inhaled. ApLundell (talk) 22:27, 25 July 2021 (UTC)


 * One of the characteristics of the traditional 555 was quite powerful output transistors for a thing that size. It could source something like 200mA if I remember right.  I wonder if that tiny CSP one can do anything like that. 2601:648:8202:350:0:0:0:2B99 (talk) 02:12, 26 July 2021 (UTC)


 * good points. thank you both! Aecho6Ee (talk) 17:44, 28 July 2021 (UTC)