Atmosphere Definition and 407 Threads

An atmosphere (from the greek words ἀτμός (atmos), meaning 'vapour', and σφαῖρα (sphaira), meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in place by the gravity of that body. An atmosphere is more likely to be retained if the gravity it is subject to is high and the temperature of the atmosphere is low.
The atmosphere of Earth is composed of nitrogen (about 78%), oxygen (about 21%), argon (about 0.9%), carbon dioxide (0.04%) and other gases in trace amounts. Oxygen is used by most organisms for respiration; nitrogen is fixed by bacteria and lightning to produce ammonia used in the construction of nucleotides and amino acids; and carbon dioxide is used by plants, algae and cyanobacteria for photosynthesis. The atmosphere helps to protect living organisms from genetic damage by solar ultraviolet radiation, solar wind and cosmic rays. The current composition of the Earth's atmosphere is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms.
A stellar atmosphere is the outer region of a star and typically includes the portion above the opaque photosphere. Stars with sufficiently low temperatures may have outer atmospheres with compound molecules.

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  1. J

    Meteorology atmosphere temp question

    Homework Statement Could a liquid thermometer register a temperature of -273° C when the air temperature is actually 500° C ? Where would this happen in the atmosphere, and why ? The Attempt at a Solution I have no idea. If someone could just give some possible tips on what it may...
  2. J

    So why does the atmosphere block gamma rays but not UV rays?

    Or light rays for that matter. Where does the window open in the atmosphere on the em spectrum, UV? Why is that?
  3. W

    Is Earth's Thin Atmosphere Caused by the Moon?

    I read somewhere that Earth's moon is a cause for Earth's relativly thin atmosphere, is that true. If so would that mean if the moon was smaller we would have a thicker atmosphere?
  4. C

    If the Earth were adrift in space, what would happen to its atmosphere?

    If the Earth were slung out of its orbit, away from the Sun's light and warmth, what would happen to its atmosphere? How quickly would it cool? The core and magma would provide some warmth to the surface, but even with our greenhouse gases holding in heat, I assume that everything would turn...
  5. J

    How does sun rays pass through the atmosphere layers?

    Light requires some medium to pass through, what's the medium in the space, and How does sunrays enters into the earth.
  6. W

    Escape velocity in the atmosphere

    I have a question on escape velocity. Would a planet with 60% of Earths gravity support a relatively thick atmosphere? It would contain nitrogen, oxygen, water vapor and carbon dioxide. This planet would get the same amount of solar radiation and luminousity the Earth does. Would the gases...
  7. D

    Calculating the mass of the earth's atmosphere

    Homework Statement Given that the radius of the Earth is 6.4 x 10^6 m, the total mass of the Earth's atmosphere is approximately________kg? Choices: a) 5 E16 b) 1 E18 c)5 E18 d)1 E20 e) 5 E9 Homework Equations What is the depth of the Earth's atmosphere? What is the density...
  8. J

    Can a planet/moon's atmosphere generate a magnetic field?

    Excluding another large planet in close proximity, can a planet/moon's atmosphere generate a magnetic field, or is it only generated from the core? If the atmosphere was charged enough with electrical storms perhaps? Thoughts?
  9. J

    Year 12: Cambridge Physics Problem (Distance of O atom in atmosphere)

    At an altitude of about 100km above the Earth's surface, the density and temperature of the atmosphere are about 10^-14 kg/m^3 and 2000K, respectively. At this altitude, the major constituent of the atmosphere is atomic oxygen. Use this information to estimate the pressure of the atmosphere at...
  10. R

    The atmosphere of titan and mars

    If Mars' mass is .1 Earths and the pressure of its atmosphere is .6 kPa then why is Titan's atmosphere 147 kpa when its mass is .02 Earths? Apparently mass is not much of a factor in determining a planet's atmosphere.
  11. C

    Distribution of molecules throughout the atmosphere

    Hi I was wondering if anyone knows about how molecules are distributed throughout various layers of the atmosphere. My assumption is that most molecules would be more abundant in the troposphere and decrease throughout until the mesosphere. does anyone know a little more about this or any...
  12. S

    Carbon dioxide density & distribution in the atmosphere

    carbon dioxide is heavier than air, so how there is a layer of CO2 is forming around the atmosphere?
  13. P

    Density of Venus' atmosphere - historical

    Hello! I'd like to know when the high density of the atmosphere of Venus was first determined or suspected. Was it with the Russian probes that the first evidence came that the atmosphere was much more dense than the Earth's? Or had there been other indications earlier in time that such was...
  14. Q

    Can the Moon sustain an atmosphere after terraforming?

    Hi, I am trying to calculate if moon can possibly hold an atmosphere if we decide to terraform it. The assumption is that it is somehow miraculously completely shielded from Solar Wind, let's say by strong Earth like magnetic field. I found somewhere on the web, that atmosphere of any...
  15. A

    Why is the Temperature of Water Low Than Atmosphere?

    Hello guys, This has been my observation and a general physical significance of water, maybe. I would like to know, why does the water keep its temperature low from the atmospheric temperature? For example, the room temperature is 29°C and the water kept in steel bucket may measure somewhat...
  16. M

    How much energy is require to remove a small amount of CO2 from the atmosphere?

    Homework Statement Estimate how much energy is required to remove a small amount of CO2 from the atmosphere if we were to do a clean-up operation to take back greenhouse gas released into the atmosphere by human activity. Give the estimate in energy per molecule of CO2. Compare this with the...
  17. P

    Calculate the energy density of the Earth's atmosphere

    Not really homework, just practice for a midterm, I also have the correct answers; but I guess this is the correct section. Homework Statement In the Earth's atmosphere we have an electric field with a vertical direction down towards the earth. The lower part of the atmosphere has a typical...
  18. F

    Lifetime of CO2 in Mars atmosphere

    Homework Statement Estimate the lifetime of CO2 in the atmosphere of Mars. Homework Equations The Attempt at a Solution What is he asking? How long has the CO2 been in the atmosphere? It just seems rather vague.
  19. M

    Differing Mass, Same Size, In Atmosphere- gravitational acceleration

    In a vacuum, gravity acts on different mass exactly the same. However, what about on earth...what is the relationship between two identical sized objects, in the exact same atmosphere...but of different mass? For example, dropping two identical sized bowling balls from height of 10 meters...
  20. S

    What is the ratio of oxygen in the atmosphere at different heights?

    Homework Statement Air at sealevel is composed of 80% nitrogen and 20% oxygen, but at the top of Mount Everest the composition of air is different. Give an expression for the ratio (f_O) of oxygen in the air as a function of height z above sealevel, assuming the temperature T is constant and...
  21. A

    Balance of oxygen in the atmosphere

    Is the amount of oxygen in the air always the same?if yes,how?or if not, how not?
  22. L

    Maximum Wind Speeds and Atmosphere Loss on Small Planets

    I was reading the Mars article about dunes and I wondered to myself, is there a limit to wind speeds before the wind escapes the planet's gravity and enters into the upper atmosphere, or dissipates in space? Would this be a factor in atmosphere loss that the small planets all seem to have...
  23. C

    Atmosphere on a hypothetical tidally-locked Earth

    Hey all, I have a few questions about the effects of tide-locking on a planet's atmosphere. Any insights or estimates would be helpful. Thanks! (Assume, hypothetically, that an earth-like world was tidally locked to its sun--the day side would be perpetually blazing hot, and the night side...
  24. M

    Could Mars's collision with orbiting asteroid reactivate atmosphere?

    As I understand it, Mars has 2 asteroids in orbit. One slowly moving away from Mars, the other on an orbital collision course. Could the collision possibly be violent enough to liquify the planets mantle? If so, would Mars re-establish a magnetic field? Is there sufficient ice in the polar caps...
  25. M

    Why do meteors burn up in our atmosphere / why are they moving so fast?

    Hi, I have a question, that I kind-of know the answer to, but then have a follow-up question: Why do meteors burn up in our atmosphere? The answer must be that they are "slowing down" causing friction/air pressure that turns into heat and combusts. But then, why are they moving so fast in...
  26. fluidistic

    Stefan-Boltzmann's law, atmosphere

    Homework Statement To understand why it's hotter inside a car than its surrounding when exposed to sunlight, let's try a simplificate model that is equivalent to what happens with the atomosphere. To start, let's suppose that the Earth's surface is flat and that it behaves like a black body...
  27. L

    Show that the atmosphere is neutrally stable

    Homework Statement Assume that the atmosphere is dry, and that its temperature profile may be approximated by a linear function in height using a constant lapse rate: T = T_0 - \gammaZwhere T_0 is the ground temperature. Also assume that the pressure can be approximated the following...
  28. E

    Is 85Kr from nuclear fuel rods really a significant risk to human health?

    Krypton-85 85Kr is a beta emitter with 687keV maximum energy and 10.7 year half-life. It's produced by uranium fission with 0.27% yield (137Cs and 90Sr: 6%). Here is a report, a bit old and in French, but figures read the same in English anyway...
  29. M

    Mars Atmosphere And Magnetic Field

    So often I see shows on TV discussing the seemingly inevitable terraforming of Mars by humans. These shows generally talk about the challenges in creating an atmosphere (basically, heating up the frozen carbon dioxide to release greenhouse gases), thereafter releasing all of Mars' water, and...
  30. J

    Color of Sky Without Atmosphere or 50 Times Densers

    Color of Sky Without Atmosphere or 50 Times Denser What would be the color of the sky if the Earth had no atmosphere? Since the scattering of light is due to the fact that the wavelengths of blue are small enough to be obstructed by the particles in the atmosphere, whereas longer wavelengths...
  31. A

    Pressure against atmosphere pressure

    Homework Statement See problem 3 Homework Equations The Attempt at a Solution In the solution, the interval for the integral of pressure is from P_{0} to the required P. However, I wonder that why we don't use net pressure as the intervals. i.e. From P_{0}-P_{1} to P-R Where...
  32. B

    How does the atmosphere affect human weight on Earth?

    Does Earth's thick layer of atmosphere push down on us, increasing our weights drastically?
  33. G

    Deriving/Calculating the Mass of Earth's atmosphere

    Homework Statement Consider an isothermal atmosphere with temperature T_{0}. Show that the mass of this atmosphere on a planet with the same radius at earth, a, and the same gravity, g, is greater than \frac{4\pi a^{2}p_{s}}{g}. If the scale height of this isothermal atmosphere is 7 km, by...
  34. N

    Why are X-rays absorbed in the atmosphere.

    X-ray observations of outer space are usually made from orbiting platforms. Yet radio and optical astronomy seems to work pretty well. I got to thinking that it seems odd for the highest energy electromagnetic radiation to be so well blocked by Earth's atmosphere...I would have thought...
  35. G

    Why the atmosphere spins with the Earth

    The mantle of the Earth spins at about 1000mph at the equator and at 0mph at the poles. The atmosphere spins in unison and I've never fully understood why. I would be very grateful for a scientific explanation.
  36. F

    In Atmosphere Ion Drive(Assess Viability For Spacecraft)

    For starters, watch this video to see what I'm talking about. It has been done, so I know it can work, but I want to assess viability for maneuvering while in the thermo-sphere (space shuttle/ISS orbit) You can skip to 2:20...
  37. S

    Why does Venus have an atmosphere?

    Neither Mercury, Venus or Mars have a planet generated magnetic field and the lack of this is given as the reason why Mercury and Mars have lost their atmosphere to the solar wind. But Venus quite clearly still has it's atmosphere - why has it not lost it too? Internet investigations describe...
  38. T

    Velocity and leaving earth's atmosphere

    I have a basic understanding of the escape velocity principles when it comes to an object lacking propulsion such as a bullet or a baseball. If the projectiles speed is not equal to 11.2km/s (or whatever EV equals with atmosphere), then the projectile will return toward Earth's center of mass...
  39. J

    1 D steady state diffusion equation in the atmosphere

    Hello, I have a 1-D steady state (dc/dt=0) differential equation in the atmosphere. It looks like follows, K*C'' + (K'+K/H)*C' + (1/H*K'- (K/H^2)*H'- (L+Si))C + S = 0 where, C = concentration of the contaminant in the atmosphere at different heights z K = vertical diffusion...
  40. N

    How do scientists study the past atmosphere?

    How do scientists determine levels of atmospheric gases in the past ?
  41. M

    Origin and Development of Earth's Atmosphere

    Hello, I'm a newbie so please tell me if I'm doing anything wrong :) I am working on a portfolio for school and I have chosen the topic "Air". As I was all set and ready to start, I realized that I didn't know the first thing about air. By now I know that what we call "air" is in fact the...
  42. C

    Why Don't Jet Airplanes Heat Up Like Probes Re-entering Earth's Atmosphere?

    If a probe entering the Earth's atmosphere heats up because it encounters the atmosphere, then why don't jet airplanes (for example) also get really hot? They are flying around in the same atmosphere that heats up the probe when it re-enters the Earth's atmosphere.
  43. T

    A question about atmosphere layers

    Hello there!Layers of our atmosphere are said to be counted according to their temperature, then why don't scientists include the places where temperature is stable with altitude (as shown in the picture) as distinct and additionnal atmospheric layers?Thank you
  44. K

    Variations in Refractive Index of atmosphere with altitude ?

    Variations in Refractive Index of atmosphere with altitude ?? The queries i have are related to refraction of light. 1. How does the refractive index of air vary with the altitude ? If possible explain the reason for change. 2. Does the amplitude of a wave change during refraction?
  45. S

    Understanding the Principle of 'Skipping' Off the Atmosphere

    I'm researching this for application in a story. I've looked at a dozen or so websites, which all explain that the principle of skipping off the atmosphere (like skipping a stone on a pond) works, but they don't explain exactly how. For what reason does an object hitting the atmosphere at a...
  46. P

    Computation of direct warming of atmosphere by burning oil

    What is wrong with this computation ? (1) Mass of Earth's atmosphere is 5 x 10^18 Kg. (2) The heat capacity of dry air, Cp, is 1 KJ/Kg-K (3) BP states that the amount of fossil fuels burned worldwide in year 2008 was 11,295 million tons. Round that to 11 billion tons. (This may be...
  47. B

    Given g and T, find volume & mass of atmosphere

    I'm working on building a world, and I have established the mass and radius of the planet, as well as its distance from its star and mean surface temp. I have determined g (10.33 m/s^2) at sea level, and wonder if this plus the mean surface temp is enough to get a rough idea of the...
  48. FtlIsAwesome

    Jovian planet with breathable oxygen atmosphere.

    Could it be possible for a jovian planet to have an oxygen atmosphere breathable by humans? Let's say that the humans live in blimp-like stations, and the jovian planet is small like Neptune to reduce the high gravity.
  49. FtlIsAwesome

    Can a human breathe in an atmosphere that has a gas other than nitrogen?

    Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%. From Wikipedia, Earth's Atmosphere Is possible for a human to breathe in an...
  50. H

    Atmosphere, carbon dioxide and water vapour help?

    atmosphere, carbon dioxide and water vapour help?? (c) One cubic metre (1 m3) of atmosphere at sea level contains 3.80 × 10(power of)2 ppm of CO2 and 5.00 × 10(power of)3 ppm of water vapour. If there is a total of 2.6 × 10(power of)25 molecules in 1 m3 of air, calculate how many...
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