# Tag Info

63

The first handful of hits on Google actually return incomplete and even wrong answers (e.g. "Because the Moon is much brighter" which is plain wrong, and "Because the Moon is closer" which is incomplete [see below]). So here's the answer: As you mention, when light enters our atmosphere, it goes through several parcels of gas with varying density, ...

63

The light from the moon is light being reflected from the sun. This is at least one reason you should not expect the Moon to have the same color. Sunlight hitting an e.g. blue object would appear predominantly blue and similar. So the color we might expect to see from the Moon is going to be adjusted by the color properties of the Moon's surface. As it ...

42

Yes, a tectonically inactive planet can retain a long-term atmosphere. You make the connection that a lack of plate tectonics on a planet indicates a "dead" core and thus said planet has no magnetosphere. As such, I'm going to interpret your question as, can a planet without a magnetosphere retain an atmosphere long-term? As proof, I offer up Venus....

42

Reflected moonlight is actually slightly reddened compared with the incident solar spectrum (Ciocca & Wang 2013). That same light is then transmitted through out atmosphere in exactly the same way as sunlight. Any phenomenology (which appears disputed) as per the claim in the question is purely down to the nuances of our colour perception. Figure 8: ...

34

Venus has a strong ionosphere that protects it against violent solar winds. So, even though Venus has no intrisic magnetic field, it has an effective, induced magnetic field due to the interaction between the solar winds and the atmosphere, that protects it against solar winds. Venus atmosphere is thick enough to have a consequent ionosphere, that would be ...

28

The simple answer is that it does, but it's not bright enough to be visible to the naked eye. Earth's atmosphere scatters the moon light just like sunlight. The full moon (like the sun) fills about 1/2 of 1 degree of the sky, the entire sky being 180 degrees, give or take, so the full moon fills less than 1 part in 100,000 of the night sky, so there ...

27

In an isothermal atmosphere, the exponential scale height of the atmosphere is $$h \sim \frac{k_\mathrm B T}{\mu g},$$ where $g$ is the gravitational field, $\mu$ is the mean mass of a particle and $T$ is the temperature (in kelvin). i.e. The pressure/density of the atmosphere falls exponentially, with an e-folding height given by the above expression. I ...

24

There is a simple$^*$ way to know the total mass of the atmosphere: measuring the pressure it exerts on the surface, which necessarily integrate all of the atmosphere above ground level. If you take an atmospheric pressure of $1\cdot10^5$ Pa, it is equivalent to a force of $1\cdot10^5$ newton over one square meter. Multiply by the area of the planet in ...

23

Surprisingly, the moonlight is actually slightly warmer color than sunlight, as the moon reflectance is higher for longer wavelengths. Yet, on clear nights, with the full moon high in the sky (as little atmospheric influence as possible) the landscape around us appears blueish, because of the Purkinje effect: at low illumination levels our red color ...

21

The Moon's atmosphere is very thin compared to the Earth, so thin that it is usually said to have no atmosphere. The Moon's gravity is not strong enough to retain lighter elements, so they escape into space. Apollo 17 carried an instrument called the Lunar Atmosphere Composition Experiment (LACE). Oxygen is not listed as one of the elements it found on ...

21

Our atmosphere is only transparent to visible light, In most other wavelengths, some or all of the light is absorbed Image from Wikipedia, adapted from image by NASA Our eyes have evolved to take advantage of the transparency at these wavelengths. If we had evolved in an atmosphere with a very different mix of gases. One in which visible light was ...

21

It varies. The best astronomical sites have a visual band extinction of 0.1 mag, which means that only $\sim 10$ per cent of light is absorbed/scattered in the atmosphere. In dusty, smoggy or polluted sites, this can easily reach one magnitude of extinction, which means that 60 per cent of the light is scattered. These numbers are per airmass - which ...

21

The chemistry of Titan's atmosphere is complex, with reactions occurring between carbon dioxide, oxygen, carbon monoxide, hydroxl, and other compounds. This means that carbon dioxide production and destruction takes place through a variety of reactions (Samuelson et al. 1983), some spurred by ultraviolet light from the Sun (and hence photodissociation). In ...

18

There is an interesting article on the magnetosphere of Venus on the ESA Science and Technology site. You can find the article here and it will probably answer your question. The article states, like you did, that some planets, like Earth, Mercury, Jupiter and Saturn, have magnetic fields internally induced by their iron core. These magnetic fields shield ...

17

The easiest way to determine the magnitude of a given star is probably to use the Pogson relation. The idea is to determine the magnitude of a star knowing the magnitude of a reference star; it is thus quite easy, using a well-known reference as Vega or Sirius. The Pogson relation is given by: $$m_1-m_2=-2.5\ log\ \left({\frac{E_1}{E_2}}\right)$$ where $... 14 In theory one should just be able to determine the difference between the spectra during the star's eclipse of the exoplanet (starlight alone) and the spectra of the star and exoplanet together, but in reality equipment is not precise enough for this. To remedy this problem, the analysis is integrated over many eclipses. Some other calibrations are made as ... 13 There are different ways to model something. From what you're asking, there are two main types of modeling: forward modeling and inverse modeling. Forward Modeling In this type of modeling, you have a specific model that defines the "current" state of your system. In the case of exoplanet atmospheres, it'd likely be something that defines the molecular ... 13 A number of brown dwarfs have had 'surface maps' created using the light from those stars. In 2013, observations of 2MASS J22282889–4310262, a brown dwarf 35 light years away, were published. These were made using the Hubble and Spitzer space telescopes and were able to show changing light patterns and distinct layers of material at different altitudes in ... 12 You are right that it's surprising that Titan, being just a moon, has a thick atmosphere. Usually, the answer includes magnetism: Earth has an atmosphere because the liquid magma inside the planet produces a magnetic field. This magnetic field changes the paths of the particles in the solar wind, thus preserving the volatile gases intact. Mars did use to ... 12 Doing a bit of reading up on this, I might have an answer, though credit where credit is due, the answer isn't really mine: https://www.reddit.com/r/askscience/comments/3wsy99/why_is_neon_so_rare_on_earth/ When the planets coalesced, it's likely that there was very little ices/gas around the inner planets when they formed and the Earth's atmosphere and ... 12 It does actually, but the human eye can't see it. But long exposure photography can see it easily. Or this photo, taken about three hours after sunset and lit by a nearly-full moon. 12 Gravity is only important insofar that it is capable of compressing the material to high densities. Whether that material is capable of solidifying depends on the competition between Coulombic potential energy and the thermal energy of the particles. The former increases with density, the latter increases with temperature. A dense plasma can still be a gas ... 11 Yes the Sun has an atmosphere. Disclaimer: I'm not sure if you meant this, but your question implies the Sun is a planet. It, of course, is a star and not a planet. Just wanted to make that clear. What is an atmosphere? When you ask if the Sun has an atmosphere, you're actually asking a tricky question. What do you mean by atmosphere? How do you define ... 11 For a liquid, hydrostatic pressure is$\rho g h$where$\rho$is density (this is always the same for all water) g is gravitational acceleration and h is depth. The gravitational acceleration on Europa is 1.3$\text{m/s}{}^2$(compared with 9.8$\text{m/s}{}^2$on Earth). But on Europa there is 20km of ice floating on the water. As a rough estimate, the ... 11 There is a number of issues with the question, but let me sketch out some kind of answer, so you get something out of it. The atmosphere of a neutron star is a topic that's a bit speculative. Estimates vary a lot. Regardless, neutron stars can have an atmosphere - sure, gravity is huge, but they are also extremely hot. Some molecules are bound to jump up a ... 10 The loss of the Martian atmosphere can be mostly attributed to its mass. The reason why Earth still has an atmosphere made of lighter elements is because with larger mass comes larger escape velocity, which is the speed at which an atom's kinetic energy overcomes the gravitational potential energy of its planet. The distribution of speeds of most gasses can ... 10 First, it's a great question. Mostly the answer is straight forward, so I can answer it, but it's still a great question. and I'll add a similar, but slightly more detailed picture to the one you posted. Source You're right that there is a clear difference between Earth's surface where liquid water can exist, evaporate, make clouds, rain and repeat. ... 10 Suppose the atmosphere has a density that decays exponentially with height. e.g. $$\rho = \rho_0 \exp[-h/h_0]\ ,$$ where$\rho_0$is the density at some surface and$h_0$is a characteristic height scale on which the density decreases. If we integrate this funcion from$h=0$to$h = \infty$, then this gives a finite result.$\$ \int^{\infty}_0 \rho_0 \exp[-...

9

If so by how much does it "spoil" the view of stars and galaxies etc. There are several very different issues related to your question. Let's tackle them one by one. Atmospheric refraction Yes, the Earth's atmosphere refracts light. One notable effect is that objects near horizon appear higher than they should be. Therefore, the Sun (or any other object) ...

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