Wikipedia:Reference desk/Archives/Science/2015 September 27

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September 27

Midges active months in Scotland

Is there a known range of months during which midges are liable to bite people in Scotland.

Visibility of nearby nebulae

Recent spectacular photos of the Veil Nebula (news story) bring up a nagging question. If a nebula is six times the size of the full Moon and we don't see it from Earth with the naked eye, I think that this means you wouldn't see it with the naked eye if you were standing on a planet right at the rim of it, or inside it. This is because the light received from astronomical objects according to the square of distance, but the portion of the sky they occupy decreases by the same amount. So my assumption is that you would see the very center of the Crab Nebula Orion Nebula as being "as bright as starlight" from some nearby planet, because it is seen with the naked eye here as one star in Orion's sword (note though that stars themselves are much brighter than they look because they occupy a smaller area we can see, so I'm not quite sure what that really means). But we wouldn't see the outer part, and we wouldn't see the Veil Nebula at all because according to the article the whole thing (I think) is apparent magnitude 7. Anyway...

• What nebulae are bright enough that from nearby you would see some or all of them as naked-eye objects?

• There are apparently some number of nebulae taking up fairly large portions of the sky. When distant galaxies are examined within those regions, is the nebula background basically being subtracted from the pictures to make them look like they are set against the "blackness of space"?

• Is there some faint level of background that can be seen in larger portions of the sky, so that there is a certain faint "nebula" like quality ino ]]the space around us? Wnt (talk) 02:18, 27 September 2015 (UTC)

I'll just point out that the Crab Nebula is actually in the constellation Taurus. You're thinking of the Sword of Orion. --TammyMoet (talk) 10:40, 27 September 2015 (UTC)

DERm, ooops. Yeah, Orion Nebula in Orion is the combination I was looking for. :P Wnt (talk) 15:59, 1 October 2015 (UTC)

Falling block and Newton's 3rd law

First year university student here. Say a wooden block is dropped to the ground from the top of a cliff to the (horizontal) ground below. The block's velocity increases at a constant rate (in the negative direction), and the acceleration is -9.8 m/s^2.

An acceleration-time graph would have the acceleration negative for the time the block is falling, then very quickly spikes up in a fraction of a second to a very high velocity. This is because the velocity goes from a non-zero quantity to zero very quickly (assuming the block does not bounce back upward), meaning the total area of the acceleration-time graph must be zero, so there must be a high acceleration in the positive direction, which must come from a force exerted by the ground upward.

What my problem is, is Newton's Third Law: "When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body." The only forces acting on the block when it is falling are gravity (ignoring air resistance), which is F=mg. But if that's the case, then according to the law, the ground would exert the same force upwards of mg. My question is, why is the acceleration on the block from the ground so high? Is this a violation of Newton's law? Thank you!! 70.54.112.243 (talk) 03:33, 27 September 2015 (UTC)

(The end of your first paragraph appears to be missing.) The ground does exert a great deal of force on the block, which might very well shatter it. Of course, in the real world you don't have the perfectly inelastic collision you describe. So, the ground right under the block deforms, the block deforms, and possibly both shatter or leave an indentation in the other. StuRat (talk) 03:40, 27 September 2015 (UTC)

Sorry about the first paragraph! I moved it to the second paragraph and forgot to erase it. And thank you for your reply. 70.54.112.243 (talk) 03:51, 27 September 2015 (UTC)

The force that stops the block at the bottom is not gravity but a contact force that's ultimately due to some complicated combination of electromagnetism and the Pauli exclusion principle. It's easily able to counter the acceleration of gravity because gravity is extremely weak compared to other forces of nature.

Newton's 3rd law does imply that an upward gravitational force of mg acts on the earth while the object is falling, but the resulting acceleration is too small to notice since the earth's mass is so large. It also implies that the large upward contact force on the block that stops it is matched by a large downward contact force on the earth. The net acceleration of the earth is again too small to measure, but the force will generate transient waves in the ground that could be detected by a seismograph. -- BenRG (talk) 04:15, 27 September 2015 (UTC)

When the block hits the floor, Newton's second law also applies: the net force on an object is equal to the rate of change. The downward force from gravity is still m*g, but the force upwards from the ground will be much larger because it has to "decelerate" the block. If the deceleration (acceleration in upward direction) is 100*g, then the net force on the block is F_n=m*100*g; therefore the force from the ground must be F_ground=101*m*g (since F_n = F_ground - F_gravity or 100*m*g = F_ground - m*g). If the force from the ground was only m*g, the net force would be zero, meaning the block would keep the same velocity, which clearly isn't possible.

Only when the block has come to rest on the floor (velocity is zero) the net force becomes 0, so at that moment the force from the ground equals F_ground=m*g. Ssscienccce (talk) 16:16, 27 September 2015 (UTC)

And the third law applies the whole time: during deceleration, the ground exerts a force of 101*g on the block, but the block also exerts a force of 101*p on the ground. It may not be obvious that the ground experiences such a force, but replace the ground with the roof of a car for example: the weight (=force) of a brick won't damage it, but a brick dropped from a cliff will, because the force the brick exerts on the roof is equal (in magnitude) to the force the roof exerts on the brick. Ssscienccce (talk) 18:34, 27 September 2015 (UTC)

Sulfur in the Bible

The Old Testament

• Genesis 19:24 Then the LORD rained upon Sodom and upon Gomorrah brimstone and fire from the LORD out of heaven;
• Deuteronomy 29:23 And that the whole land thereof is brimstone, and salt, and burning, that it is not sown, nor beareth, nor any grass groweth therein, like the overthrow of Sodom, and Gomorrah, Admah, and Zeboim, which the LORD overthrew in his anger, and in his wrath:
• Job 18:15 It shall dwell in his tabernacle, because it is none of his: brimstone shall be scattered upon his habitation.
• Psalms 11:6 Upon the wicked he shall rain snares, fire and brimstone, and an horrible tempest: this shall be the portion of their cup.
• Isaiah 30:33 For Tophet is ordained of old; yea, for the king it is prepared; he hath made it deep and large: the pile thereof is fire and much wood; the breath of the LORD, like a stream of brimstone, doth kindle it.
• Isaiah 34:9 And the streams thereof shall be turned into pitch, and the dust thereof into brimstone, and the land thereof shall become burning pitch.
• Ezekiel 38:22 And I will plead against him with pestilence and with blood; and I will rain upon him, and upon his bands, and upon the many people that are with him, an overflowing rain, and great hailstones, fire, and brimstone.

The New Testament

• Luke 17:29 But the same day that Lot went out of Sodom it rained fire and brimstone from heaven, and destroyed them all.
• Revelation 9:17 And thus I saw the horses in the vision, and them that sat on them, having breastplates of fire, and of jacinth, and brimstone: and the heads of the horses were as the heads of lions; and out of their mouths issued fire and smoke and brimstone.
• Revelation 9:18 By these three was the third part of men killed, by the fire, and by the smoke, and by the brimstone, which issued out of their mouths.
• Revelation 14:10 The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:
• Revelation 19:20 And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone.
• Revelation 20:10 And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
• Revelation 21:8 But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.

When the Bible talks about sulfur (brimstone), it's bad, it really really really is BAD! Nothing can be worse than sulfur.

However, I don't think the Middle East was a land that produced large quantities of sulfur. Today, many oil producing countries (e.g., Saudi Arabia and U.A.E.) sell sulfur for industrial use as byproducts. I don't think there were oil fields that produced tons after tons of sulfur during Biblical Ages.

Where did they learned about sulfur? -- Toytoy (talk) 06:29, 27 September 2015 (UTC)

See History of Sulphur. Nowadays, sulphur is mostly a by-product of oil production, but historically it was found as a raw element in places where there are or were volcanoes (and there are a fair few extinct volcanoes in the Middle East) - being associated with volcanoes helps sulphur's hellish image. They may also have found some of it as a by-product of smelting metal ore (many copper ores, for example, contain sulphur). Sulphur was valued for medicine and pest control in ancient times, and that's partly because it produces such horrible noxious fumes when you burn it. Smurrayinchester 07:00, 27 September 2015 (UTC)

All the Miracles of the Bible by Herbert Lockyer (p. 40) says that at Mount Usdom (?), allegedly the Biblical Sodom, there is a "stratum of marl mixed with free sulphur". Alansplodge (talk) 08:10, 27 September 2015 (UTC)

Didn't Jesus say "Sulfur the children to come unto me"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:19, 27 September 2015 (UTC)

Salt domes sometimes contain elemental sulfur: The caprock above the salt domes is sometimes the site of deposits of native sulfur. Salt domes are often associated with oil reserves.

Some historians claim that Persians used sulfur as a "chemical weapon" against the Romans, in Eastern Syria, in the 3rd Century AD.

this 19th century book writes about "The great sulphur mines of Khameer, in the Persian Gulf; are rented by the Imaum of Muscat, who works them, and trades with the produce." Ssscienccce (talk) 19:04, 27 September 2015 (UTC)

Do banana actually causes to constipation?

I searched on the internet and I saw two opinions about that. What is the true? Are there scientific studies about this issue? 37.73.192.222 (talk) 11:28, 27 September 2015 (UTC)

When I first saw this question I thought it would be easy to answer, as green or greenish bananas (as every body knows from their Grandmothers) helps with diarrhoea because of the higher starch content. Whilst on the otherhand, ripe, slightly brown bananas, have a lower starch and higher sugar content and reduce constipation and both contain the all important fibre. However, the scholarly articles all seem to concentrate, either on constipation or diarrhoea and with the additions of rice bran or some-other other stuff. Of course, this handed down wisdom could all have been a cunning ploy by our Grandmothers to induces some type of placebo effect upon us so the we didn't have to get taken down to a doctor for an expensive consultation and prescription. Leave that up to you deside (and if I say the Sun is going to rise again tomorrow do I need to come up with a scientific study to prove an everyday common-sense observation)--Aspro (talk) 12:41, 27 September 2015 (UTC)

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4291444/ : Unripe bananas contain 100-250 mg tannins/100 g and have high amylase-resistant starch content. Thus, they can cause or aggravate pre-existing constipation. This property has been used in the BRAT (banana, rice, apple sauce, and toast) diet for diarrhea. As bananas ripen, the quantities of tannins and amylase-resistant starch decrease, while soluble sugars accumulate. Ripe bananas contain 3 g fiber/120 g, mostly in the form of soluble fiber.

So unripe bananas contain more constipation-causing tannins and starch than ripe bananas. Ssscienccce (talk) 12:45, 27 September 2015 (UTC)

Have come across this: Bananas And Constipation: The Real Story. It may be not scientific and peer reviewed but I think my Grandmother would agree with every word, as would anybody that took her advice and found it works in practice.--Aspro (talk) 13:56, 27 September 2015 (UTC)

Note that bananas might not have been so much to cure diarrhea as to restore the potassium balance which can be messed up as a result of diarrhea. StuRat (talk) 13:33, 28 September 2015 (UTC)

Good point Stu. For someone who has galloping diarrhoea or persistent vomiting, they can lose potassium which messes up their potassium/magnesium balance which can have a big effect on their metabolic water balance and aggravate their malady even further (i.e., go on to cause constipation). In parts of the world where they don't have modern rehydration fluids, bananas are often recommended as the source of the required potassium. --Aspro (talk) 14:07, 28 September 2015 (UTC)

Blood borne illnesses

Are blood borne illness transmissions common from gyms or contact sports? Why or why not? 2A02:C7D:B91D:2200:4964:3DE1:240A:360A (talk) 11:31, 27 September 2015 (UTC)

It's unlikely that this would be common - because it's unlikely that the blood from one competitor to get past the skin of another. Surgeons (for example) are able to operate on HIV positive individuals without too many risks - unless they get 'stuck' by a used needle or scalpel, then it's suddenly a cause for massive concern because the patient's blood may now have come into direct contact with the surgeon's blood. Everything depends on the individual disease we're talking about - but in general, it requires that the bodily fluids from the infected person to get inside the body of the uninfected person. [1] says that percutaneous transmission is worse - that's when something with infected blood is stuck physically inside your body (eg with a needle or a knife) - second most likely is when the blood gets onto a mucous membrane (inside your nose, mouth, eyes, etc) - third most likely is if it gets onto a cut or scrape in your skin - and far, far least likely is if it winds up on undamaged skin. That's not to say that precautions shouldn't be taken - blood needs to be promptly cleaned from contaminated surfaces and disinfectant applied - wounds need to be covered promptly. SteveBaker (talk) 14:47, 27 September 2015 (UTC)

Here [2] is a scholarly article that

“ reviews the most commonly reported infectious diseases among athletes and discusses the potential for transmission of bloodborne diseases in sports. ”

SemanticMantis (talk) 18:16, 27 September 2015 (UTC)

Other sources: about hepatitis B infection risk, advising vaccination , a report that mentions HBV infection among five members of a sumo wrestling club, guidelines for prevention of infection during student activities, Indiana department of health... All say that such transmission is extremely rare, only hepatitis B seems to pose a small risk, particularly during the acute infection phase. Ssscienccce (talk) 19:24, 27 September 2015 (UTC)

Note that many (most?) team sports have a Blood rule, which generally require a player who is bleeding, or has blood on their clothes to leave the field and seek treatment and replace any clothes before coming. Compliance with these rules may however be spotty. To try and encourage compliance (and for other reasons), some contact sports with high rates of such injuries specifically allow blood replacements generally without affecting normal tactical replacement allowances. Nil Einne (talk) 20:37, 27 September 2015 (UTC)

Tonight's lunar eclipse

Is this animation to scale? I'm asking to know how far I can zoom in on the moon and capture the entire eclipse and blood moon stage without having to pan. --2003:48:2E4C:B186:F881:D2C6:8E35:E907 (talk) 23:27, 27 September 2015 (UTC)

You'll probably have to pan. For perspective: the moon angular size is about half a degree; it moves across the sky at about fifteen degrees per hour; the eclipse lasts for about four hours from first entry into the penumbra until last exit from the penumbra. (Here's the article from this week's Sky and Telescope: Ready for Sunday Night’s Total Lunar Eclipse?).

So: you can expect the moon to travel around sixty degrees: you can fit your camera with around a 30mm focal length lens (in 35mm equivalent units) to capture the entire event without panning. ...But, with that lens, the moon is going to be a small dot. For example, if you shoot with an iPhone 6S, you could carefully aim and timelapse the entire event, without a pan, but the moon would only be about 30 pixels in diameter during each still image.

I usually shoot Moon through a 300mm lens (450mm in 35mm-equivalent units); or through my telescope at 1000mm (1500mm in 35mm-equivalent). That lets me frame the whole moon... but the Earth rotates so fast, I can actually see the moon drift across my view in real-time. If you don't have a tracking scope, you can re-align by hand every few minutes, depending on how fast you plan to shoot timelapse intervals.

Nimur (talk) 23:35, 27 September 2015 (UTC)

Focal length figures will probably be way off as I'm using a 1/3" CCD cam here. But at least it's 16:9. But thanks for your link, I'm checking it out. --2003:48:2E4C:B186:F881:D2C6:8E35:E907 (talk) 23:39, 27 September 2015 (UTC)

Indeed: if you are unfamiliar with your camera's conversion ("crop factor"), read 35 mm equivalent focal length to learn how to convert into "standardized" equivalent focal lengths. You can also experiment with fixed targets, or if you're really enthusiastic, you can independently measure angular field of view by marking the camera's position, and the edges of the camera's field of view, on a paper target, and then pull out a protractor. Nimur (talk) 23:43, 27 September 2015 (UTC)

Hmph, the link doesn't say much of scale either, although it has a similar image with about an equal distance the moon will pass within the time. But going by the assumption that the animation here is to scale, I've set my 1/3" CCD cam to c. 38mm, if that tells anybody anything. It's also weird to see how 1/3" CCDs have fallen so much out of use within the last decade that not even Crop factor#Common crop factors still carries it. Using a JVC GY-HD110E from 2005 here. --2003:48:2E4C:B186:F881:D2C6:8E35:E907 (talk) 23:48, 27 September 2015 (UTC)

Regarding the animation: the animation tracks with the center of the penumbra; this is, basically, an animation of the view from a tracking telescope (i.e. as it is "panning" on an equatorial mount). The scale is not the issue; the apparent motion of the moon across the sky will be many many times larger than the width of this animation.

Regarding CCDs: Unless you have a chiller - like this little toy - your CCD probably performs worse than an equivalent modern CMOS imaging sensor. More to the point, you can't find an "equivalent" modern CMOS sensor; modern CMOS will deliver a lot more megapixels, allowing you to use more sophisticated digital noise reduction and to make the call whether to trade noise against spatial resolution in post-production. The jury is still out on whether this actually yields better signal-to-noise in the unique conditions of deep sky astrophotography (which is why Orion can still sell chilled CCDs at $500!) ... but for Moon shots, it's a no-brainer: there is so much light, the modern CMOS sensor (plus a smart algorithm) will win on almost every image metric.

I race my 12 MP Nikon DX against my newer 24 MP Nikon DX, and sometimes for fun, I sometimes even race them against my phone cameras... so far, the Nikon D90 appears to be the winner. The reality is, I am usually able to destroy a good photograph by way of poor control, and poor composition, to a degree far worse than image noise could possibly contribute.

The short of it: your camera will work fine for shooting tonight's lunar eclipse; I would bite the bullet, plan to pan (which will be easier if you have some astronomy gear, but you can do it by hand on a regular camera tilt/pan tripod, too). Zoom in as much as possible to frame the entire moon; and if you're really in to it, you can use software in post-production to "stabilize" the moon across multiple shots.

Nimur (talk) 00:03, 28 September 2015 (UTC)

It's pretty funny how you're trying to sell HD to somebody who's pretty content with an SD camera, one which due to its cine-mode will make even better images in regards to contrast and color values than the shitty RED used for Mel Gibson's visually abysmal Apocalypto which looked in colors and contrast like it had been shot on a 1CCD VHS-C cam from the early 80s. --2003:48:2E4C:B186:F881:D2C6:8E35:E907 (talk) 00:09, 28 September 2015 (UTC)

For the record: I'm not trying to sell you anything! In fact, the only commercial link I posted was to a 752x582 monochrome camera - not to its six megapixel younger brother! Your camera is fine for the task. You always have the option to buy as much extra gear as you desire; and obviously, not every expensive product will actually improve your imagery; but some products can help. The cameras that shoot well in astrophotography overlap, but are not identical, to the cameras that are useful for other types of photography or video. If I were in your place, I'd spend money on an astronomical tripod mount before spending money on a different camera. Or, ... don't! Nobody said you needed to spend money in order to appreciate a lunar eclipse. Nimur (talk) 00:15, 28 September 2015 (UTC)

Yes, a moving tripod would come in handy, but it's not like I could buy one at 2:18am on a night from Sunday to Monday. --2003:48:2E4C:B186:F881:D2C6:8E35:E907 (talk) 00:19, 28 September 2015 (UTC)

Quote: “but it's not like I could buy one at 2:18am on a night from Sunday to Monday.” Eclipses are predictable - years ahead. Just plan ahead. Then you can have all your equipment and a pizza delivery, bottle of Budweiser etc., all present at the right time of the the eclipse or even occultation. It is what other people do like User:Nimur. P.S. Regarding Budweiser, I think that just listening to Claude Debussy's Clair de Lune [3] is the only intoxicate one needs with the stellar heavens as a backdrop to the stage of this amazing universe. Just a personal opinion--Aspro (talk) 15:45, 28 September 2015 (UTC)

Here is Shoot the Supermoon Eclipse Like A Pro, an interview with Bill Ingalls, senior staff photographer at NASA Headquarters, which was featured on NASA's front page today. Along the same lines, if you've been watching NASA TV today, you've been hearing "supermoon" and "blood moon." I'd like to take this opportunity to reiterate some remarks made by Mitzi Adams, a NASA solar physicist at MSFC: these words (particularly "blood moon") are not proper scientific names! First, a "super moon" is a loose way to describe a full moon that occurs near perigee. Regarding the color of the eclipse: all lunar eclipses appear reddish, because of Rayleigh scattering by Earth's atmosphere (affected by particulate matter, smoke, volcanic eruptions, and so on). "Blood moon" is a silly, unscientific term; nothing about this particular eclipse will make it more or less reddish than usual; frankly, I think it's embarrassing that anyone would use that term (including NASA's social media teams). I'm very happy that a real NASA scientist has put them straight. Nonetheless, expect to hear those terms bandied about anyway, as they've already been republished by the popular press and "social media" galore. Nimur (talk) 01:15, 28 September 2015 (UTC)

Think that the term "blood moon" came about during the years immediately after the Krakatoa eruption and has stayed in the common vernacular. These days the lunar eclipses appear (to my eyes) as orange red or red orange or red or however one wants to describe it.. A long way from the deep blood-red though. It is on record too that the Krakatoa eruption created many amazing sun rises and sunsets. So today, I think that "blood moon" is an anachronism of a time gone by when the lunar eclipses appeared blood-red. Which they would have done, because the longer the wavelength the less they gets scattered by volcanic dust. The reduced transmission through the atmosphere (at these times) of the shorter wavelengths would have left it looking very dark blood red... err..me thinks... So Blood-Moon is no longer an applicable description, which I think is what Nimur is alluding to and saying.--Aspro (talk) 16:27, 28 September 2015 (UTC)

I have no idea how the color has changed over time. Danjon scale is relevant. I don't know if manmade smog and lighting has changed the color of lunar eclipses; would be curious to hear about it. Wnt (talk) 18:52, 28 September 2015 (UTC)