Science desk
< May 2	<< Apr \| May \| Jun >>	May 4 >

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

May 3[edit]

program or website to identify stars/constellations?[edit]

Is there a website or Windows program that can take an image and identify major stars and/or constellations? Bubba73 ^{You talkin' to me?} 04:56, 3 May 2018 (UTC)[reply]

The reason I'm asking is this. I've tried several times in the last few weeks to get a time exposure photo of the Hubble Space Telescope in orbit. I haven't been able to get it. Here is some of my attempt from last night. From the sky map, it rises in the west, goes through the belt of Orion and proceeds until it goes into the shadow of the Earth. It is magnitude 1.5-1.6 just before it goes into the shadow. I took a series of 30 6-second exposures and this is the one that was at 21:58 - the point circled. (The clock in my camera is 16 second fast, but I used a different clock.) I think it should show a short streak. (In other attempts I've tried 20- and 30-second exposures.) Anyhow, I can't see a streak for the HST (there are two airplane streaks lower down.)

The problem is that I can't match the stars in the photo with the ones in the star map, so I'm not positive that I got the right area. The photo shows a lot more stars than are normally visible. You might need to take it into software and reduce the exposure to make it look more like what you actually see. The HST path is from Heaven's Above and I double-checked it with Stellarium.

So (1) - is the path of the HST in the frame? And (2) can anyone see a streak for the HST in the photo? Bubba73 ^{You talkin' to me?} 15:48, 3 May 2018 (UTC)[reply]

I uploaded the image to astrometry.net and obtained a result. If I read the map with the HST path correctly, then it may have been higher up, outside the image. --Wrongfilter (talk) 16:13, 3 May 2018 (UTC)[reply]

Thanks, that looks pretty much like the photo - the belt of Orion is near the bottom, about 1/3 of the width from the right and Sirius is about 1/4 of the way from the left, near the streak of an airplane. Then the HST is outside the frame of that photo. I don't see it in any of the photos, and they start about the time it is near Orion's belt. However, there it is much dimmer - 4th to 5th magnitude. And with it moving, maybe it isn't bright enough to show up over the background. It only gets bright just before it goes into the Earth's shadow. I can't see stars through the camera unless they are about as bright as Sirius so I take a wide-angle lens and point in the general direction. That usually works - I've gotten the ISS and Iridium flares that way. But the Hubble is not as bright. Bubba73 ^{You talkin' to me?} 17:06, 3 May 2018 (UTC)[reply]

Resolved

Bubba73 ^{You talkin' to me?} 02:48, 4 May 2018 (UTC)[reply]

That match of the image to the star map doesn't look very good. In Gemini (upper right), the green lines end nicely at the stars, but in the lower left they are way off. The green lines near the r in Canis Major should end at Sirius, which is further up and right. The scale of the map is larger than the scale of the image. Maybe the matching software assumed the wrong scale for the image, or the wrong distortion? As I read the prediction and the image, the path of HST would be expected in the upper left of the image.

When carefully examining the image, I can see three aircraft tracks: one close to Orion's belt, one down-right from Sirius and one at the same level near the left edge of the image. I also see one satellite track, in the upper right of the image, passing near ε Geminorum. It's quite bright, so it must be a big satellite. It runs in the right direction for HST, but in the wrong position. So either that is HST, and the position is off because the prediction used the wrong location for your camera or the wrong true anomaly for HST, or it was a big, unknown satellite that happend to be passing over the same part of earth, in the same direction at the same time. That's possible, of course.

As HST has no propulsion, I expect the published orbital elements to be quite accurate at all times. I've always found predictions from stellarium or gpredict of ISS passes highly accurate. But I've never seen HST myself to check, as I live too far north. PiusImpavidus (talk) 10:40, 4 May 2018 (UTC)[reply]

Indeed, the green lines are quite a bit off. The extraction image looks better and indicates that the software identified the stars correctly. I can imagine that there might be problems with capturing the huge field and the strong distortions in the world coordinate system, i.e. fitting a model to describe the mapping between pixel coordinates and sky coordinates. The green lines have to be shifted up a little bit, which makes it even more likely that HST was outside the frame. --Wrongfilter (talk) 11:03, 4 May 2018 (UTC)[reply]

I noticed the airplane trails but not the satellite trail. I've tried about six times to capture the HST in a time exposure the last few weeks but always failed (I've been able to get the brighter ISS and Iridium flares). (And I've triple checked my clock and my location.) I wrote to the Heavens Above guy about it and he says that he checked the HST orbital elements. For a couple of passes I've double checked with Stellerium and it seems to agree with Heavens Above. I'm trying again for the HST in less than 2 hours (using a somewhat wider-angle lens)... Bubba73 ^{You talkin' to me?} 23:49, 4 May 2018 (UTC)[reply]

I finally got it[edit]

First, thanks everyone! I finally got the HST but the results are not too impressive (see above). Here is a link to astrometry for tonight's photos. The map shows it just above Antila when it is its brightest (magnitude 1.9). You can see it near the left edge, about half way up. (One of the photos shows two fireflies - probably one blinking twice.) For some reason, I have my camera set to make a RAW file and a JPEG file, but tonight it made two JPEGs instead of a RAW, which gives me less to work with. The overall problem is that at magnitude 1.9 and moving (rather than staying in one place to gather a brighter spot), it is almost lost in the light pollution. These are 10-second exposures. Bubba73 ^{You talkin' to me?} 03:04, 5 May 2018 (UTC)[reply]

Since overhead passes can't happen north of Cape Canaveral this sounds like an excuse for a Florida vacation, contact the wife. Sagittarian Milky Way (talk) 18:45, 5 May 2018 (UTC)[reply]

The Hubble Space Telescope's orbit does have an inclination of 28.47 degrees, but I live at 31.3 degrees north, so it is visible at times from here. But it is usually low on the horizon, which means that light pollution interferes with it. Bubba73 ^{You talkin' to me?} 18:58, 5 May 2018 (UTC)[reply]

Leaned over mountain peaks[edit]

I was watching Lost in Space where I often see that some of mountain peaks are leaned over on a fictional planet. What are those geological features and how they form?; though I never seen pictures of such a feature taken from Earth. To understand what I'm talk about, go to [1] and look in the background. Planet Star 07:07, 3 May 2018 (UTC)[reply]

A term is overhang (rock formation). You could imagine that a nappe or thrust fault pushed the rocks out like that. But rock is not normally strong enough to sustain a large overhang, and it will collapse, perhaps making scree, but iof just left rumpled would be a more typical nappe. Graeme Bartlett (talk) 07:29, 3 May 2018 (UTC)[reply]

This reminds me of Rodney Matthews, who has done it often; also Crematoria in Chronicles of Riddick. As we don't much see such formations on Earth they seem fantastical and otherworldly, but they are also unlikely. That said, an alien planet that is tidally locked or has other strange factors affecting its winds, or unusual materials, cannot necessarily be predicted from our experience. The most fantastic formation I can think of at the moment here (apart from small stone arches and such) is the Dragon Tooth Mountains, but those go straight up. (I'm not sure what I did wrong with the link but there are lots of search results, see [2] for example)Wnt (talk) 11:32, 3 May 2018 (UTC)[reply]

I don't see how a mountain could maintain that shape and not collapse. Of course, you can do anything in a painting. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:44, 3 May 2018 (UTC)[reply]

Rock overhangs exist, but are very limited in size. However, this depends on the strength of the rock and its weight. A material like ice would do better, and low gravity would help. A bigger wildcard is the effect of living organisms - if a planet's microbes evolve carbon nanotubes they might maintain a far larger overhang in order to obtain some nutrient or respiratory need from the winds. (Which should bring us to note that, in alien contexts, there could be a smooth gradation in meaning between a "mountain" and a "tree") Wnt (talk) 13:29, 3 May 2018 (UTC)[reply]

Here's the highest overhang of a peak over the rock below. (Wikipedia has an article on it too.) Not at all like the shape in the fictional ones. --69.159.62.113 (talk) 06:19, 4 May 2018 (UTC)[reply]

I believe that a group of rock overhangs that stretch for thousands of feet appearing like a mountain tipped over exist on some planets and moons. Maybe fiction-style overhangs exist on Mercury and planets around TRAPPIST-1. Planet Star 07:32, 6 May 2018 (UTC)[reply]

Not quite on that scale, but the main crag at Kilnsey in Yorkshire overhangs by some 40 feet (12 metres) like this. Alansplodge (talk) 15:35, 7 May 2018 (UTC)[reply]

And a bit more exotically, the collapse of an overhanging cliff on comet 67P/Churyumov-Gerasimenko. Alansplodge (talk) 19:51, 7 May 2018 (UTC)[reply]

Free fall mechanics[edit]

Terminal velocity says in particular: "You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object". I don't much doubt it, but in theory this is paradoxical due to two factors: The larger the surface area, the more aerodynamic drag the falling object experiences and as such a falling horse (or any other larger animal or object) should fall somewhat slower than mouse. Also, due to larger surface area a horse should have less damage upon landing, because of more even pressure distribution upon impact (similar to ski's pressure on snow). Is it because upon impact there's a greater net force due to larger surface area which offsets those factors? 212.180.235.46 (talk) 20:02, 3 May 2018 (UTC)[reply]

Most of these issues are to do with a ^3⁄2 power scaling law with size, from the ratio of volume (length^3, controls mass and weight) and area (length^2, controls strength and air resistance). Pennycuick's Newton Rules Biology (1992) ISBN 0198540213 is one of my favourite books on this. A horse will be stronger (bone cross-section) and draggier for air resistance, but it's also heavier (more downward force to accelerate it, more momentum to damage it) and as this ratio between the two factors increases at the ^3⁄2 power, larger animals become more susceptible. Andy Dingley (talk) 20:23, 3 May 2018 (UTC)[reply]

side topic, and slightly nauseating to boot - collapsed by Tigraan^{Click here to contact me} 16:09, 4 May 2018 (UTC)[reply]

The mouse thing seems not implausible, I once threw a mouse as hard as I could against hard bathroom stuff and it squealed horribly 4 times then limped away (I accidentally glued it to my fingers while making sure it didn't escape during its humane removal. Okay no problem, just softly flick it into the container, stronger flick, still glued, even stronger, then I got scared that that might've triggered its self-preservation fear enough to contort its head enough to bite me (which would hurt like hell since I have very high pain sensitivity) and possibly give me rabies or something so I flicked it as hard as I could and it didn't become unglued till it was near top speed) A baseball is much heavier, roughly similar density and a terminal velocity of ~95mph so maybe. Sagittarian Milky Way (talk) 21:07, 3 May 2018 (UTC)[reply]

...

This does not sound like an appropriate way to remove a mouse. If you aren't able to humanely remove or kill the pest, call a pest removal specialist, so that you aren't causing unnecessary suffering for either the humans or the animals in the area; nor creating a mess.

Nimur (talk) 21:20, 3 May 2018 (UTC)[reply]

I was planning to use oil to take as much glue trap glue off as I could in several minutes (without air deprivation or touching his eyes) and depoil it with soap and gently put it in a container to release in the middle of a block wide buildingless area. (it was summer) But the oil must've only dissolved glue in the outer fur layer or something. I left it sustenance the rest of the time I was there (weeks or months) but it never stopped limping so obviously I agree glue trap and release is a not a good method. Of course letting them thirst to death on the glue trap like many people do isn't humane either. The ones stores sell that seem less likely to snap on his torso seem more humane. Sagittarian Milky Way (talk) 22:46, 3 May 2018 (UTC)[reply]

LOL, whole *point* of a glue trap is to torment the mouse... but admittedly, hiring the illegal immigrants you let in the country to kill the mouse you don't want to hurt is a way to take care of multiple problems. :) Wnt (talk) 23:58, 3 May 2018 (UTC)[reply]

This article by Cecil Adams is at least somewhat relevant. It discusses the fact that for cats, for falls above a certain height, the survival rate stabilizes at more than zero. Apparently some studies suggest that the worst height for a cat to fall is about seven stories, above that it switches its strategy from "always land on feet" to "spread out to slow fall", and that strategy sometimes works.(For cats, that is.) ApLundell (talk) 03:10, 4 May 2018 (UTC)[reply]

Less than zero??? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:51, 4 May 2018 (UTC)[reply]

I suppose that means that another cat is killed by the impact from the fall of the first. Graeme Bartlett (talk) 14:02, 4 May 2018 (UTC)[reply]

Yeah, cats land on piles of other cats. Or possibly I meant a "survival rate of more than zero", and have now fixed it. ApLundell (talk) 18:48, 4 May 2018 (UTC)[reply]

Has this been tested on real cats?Hofhof (talk) 18:32, 5 May 2018 (UTC)[reply]

Yes: "In 1987, New York City’s Animal Medical Center conducted a study of felines that had fallen from tall buildings. While 90 percent of the animals survived, most suffered serious injuries, but the cats that fell from heights of seven to 32 stories were less likely to die than those that fell from two to six stories". [3] Alansplodge (talk) 21:14, 7 May 2018 (UTC)[reply]

AD adequately explained above why the horse's terminal velocity is higher (weight goes as volume, drag as surface (roughly), hence the speed at which drag compensates weight is higher for large animals). The second question (more even pressure distribution upon impact for larger bodies) is correct in assuming that there is a higher "force" at impact for a larger body (modelling of collisions is a complex topic, but as a very first approximation you can consider that what matters is how much kinetic energy has to be dissipated in which amount of time and surface; for the same speed, the kinetic energy goes as mass hence volume, and the collision surface goes as cross-section).

As for the ski remark, I assume this is related to the fact that ski jumping exists (and is not a suicide method when practiced with care) whereas falling from an equivalent height would often be fatal. However this is not due to skis dissipating the impact over a larger surface (if anything, ski area is smaller that a cross-section of human falling flat in the snow). The key point is that as the skier falls over a downward slope while still advancing in the slope direction, the relative velocity of impact is smaller (or equivalently the kinetic energy is not completely dissipated at impact, the skier continues to move). Also, the elasticity ("wobbling") of the skis may allow to release the energy over a longer period of time, but I have no idea whether that effect is significant. Tigraan^{Click here to contact me} 16:44, 4 May 2018 (UTC)[reply]

Coming in at a shallow angle, as ski jumpers do (see Ski jumping), mimics the way planes land. They're moving at a high rate of speed horizontally, but not nearly so fast vertically. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:04, 4 May 2018 (UTC)[reply]

There's even ski flying with longer jumps than ski jumping. Olympic jumpers can have very long careers so it can't be too too hard on the joints when done well. Sagittarian Milky Way (talk) 17:24, 4 May 2018 (UTC)[reply]

Ballistic coefficient is directly relevant. Greglocock (talk) 22:04, 4 May 2018 (UTC)[reply]