# Tag Info

30

How much brighter is full-earth-shine on the moon, than full-moon-shine on earth? On average, it's about 41 times brighter -- in terms of luminosity, or a bit over four times brighter ($2.5 \log_{10} 41 \approx 4.03$) in terms of the logarithmic response of the human eye. There are two factors that come into play in the luminosity calculation: The much ...

22

Somebody suggested that the side of the moon that always faces the earth is as dark as the far side of the moon, but is that really the case? That is not the case. I'll look at two different wavelengths: visible and radio. Visible Doing astronomy from the surface of the Earth when the Moon is full is much more difficult than is doing astronomy from the ...

19

In addition to user-LTK's very good answer, it is also true that the mare which we see on the Near Side are largely absent on the far side. The basaltic flows of the mare are darker than the regolith of other areas, contributing to a higher albedo, brightness, on the Far Side. https://en.wikipedia.org/wiki/Lunar_mare

13

The far side of the Moon has sometimes been called the "dark side of the Moon", mostly because we can't see it from Earth. Apart from partial libration, we never see most of the far side of the Moon from Earth, we can see about 59% of it as it wobbles slightly as it orbits a somewhat elliptical orbit. It's more accurate to say "far side of ...

12

To answer this, one really has to understand how the geometric and bond albedos are defined. Let's start with the bond albedo since its simpler. Bond Albedo The Bond Albedo is just the fraction of energy hitting a surface that gets reflected. To simplify the process, let's say I shoot 100 photons of all the same energy at Enceladus. Of those 100 photons ...

11

The lack of a lunar atmosphere doesn't affect Earth's albedo at all, since albedo is only a measure of the diffuse reflection of a body. However, the apparent brightness of the Earth as viewed from the surface of the Moon would be affected if the Moon had an atmosphere. This, of course, would depend on the atmospheric composition of the Moon. If the ...

8

Short answer: Yes and No. Long answer: The question is a little ambiguous. What do you mean by dark and light? Do you mean that: the lunar material is lighter or darker on one side of the Moon, or the lunar surface is illuminated by more light on one side of the Moon? Part One: The color of lunar surface material on the two sides of the Moon. The side ...

8

Earth is already pretty bright due to cloud cover, with a typical albedo of .3-.35 -- that is, it reflects about a third of the visible light that hits it. That means it couldn't get more than about three times as bright even if it were perfectly reflective (albedo 1.0), which means about 1.2 magnitudes brighter. Spotting Earth from a great distance with ...

6

Eventually, yes. Interesting information about Venus: Venus is hotter than Mercury, despite being nearly twice as far from the Sun. Earth, despite being further from the Sun, receives more energy from the Sun than Venus, due to Venus's very high albedo. As you might guess by this information, the major factor that keeps Venus hot isn't how much energy it ...

5

Here's my take on it. I'm not sure what the mystery is - there appear to be two contributing factors. Both the Moon and the Earth simply reflect/partially absorb the light that is incident upon them from the Sun. The overall of albedo is of little consequence, since the reflection of any light will result in an object that appears bright against the night ...

4

Stars are far from perfect blackbodies due to scattering/reflection. This is especially true for hotter stars, because of all the free electrons, but even cooler stars can reflect a significant amount. For example, in aanda.org/articles/aa/pdf/2001/19/aa1009.pdf you will see that they use a reflection albedo of 0.30 for the K star and 1.00 for the F star, ...

4

ConnorGarcia's answer is great. The point about refraction is particularly interesting. I just wanted to describe the mechanism a bit. If you look at the sky on cloudless day, it appears blue and is brighter than the blackness of space. Where does this light come from? It is sunlight scattered by the atmosphere. So, ignoring refraction, if you look directly ...

4

If you can add a material which can reflect optical light (high optical albedo) and transmit IR light (i.e. it does not absorb or reflect too much in IR), it will reduce further heating of Venus and it will gradually cool down. You cannot lower the IR albedo (by using an IR absorbing material, for example) of Venus since it already has a thick atmosphere ...

4

The photo in your question is -- well, not exactly fake, but a composite. The biggest clue is that Earth is too close to the horizon; it would have had to be taken from within a few degrees of the boundary between the near and far sides of the Moon, and none of the Apollo missions landed there. Furthermore, take a close look at the cloud patterns. The view ...

4

Albedo is a measurement of reflected light. It varies between 0 and 1, with 0 being completely black (reflecting no light) and 1 being completely white (reflecting all light). The albedo of coal is about 0.04, which is actually very similar to the albedo of our moon. The Albedo of ice is about 0.7. Only planets and other small objects are described using ...

3

First off, I am rather certain that by diatom bloom you refer to algal bloom which is a seasonal change of sea color, at least here on Earth, the only system we have observed yet. Your question is indeed rather hypothetical, but from a astronomy/ physics points indeed an interesting one. Next, let me summarize the assumptions I am reading out of your ...

3

Assuming the major heat input is from the star (the gas giant may also radiate significant IR) then you could seed clouds or freeze the water in order to increase the albedo. Alternatively, you could increase the radiative efficiency by somehow painting the side of the moon facing away from the star black. Tricky, as no doubt this hemisphere changes with ...

2

Of course! Actually this is one of the possible ways we have in order to make Mars friendlier to humans. This technique is called Terraformation and it inludes the altering of the Mars surface's albedo. However, the feasibility of this plan is yet questionable and there are maybe better ways to achieve this increase in the temperature like CO$_2$ emissions. ...

2

As barrycarter commented, codes_300ast_20100725 has ephemerides for 300 large asteroids, generated in 2010 and supposedly valid from 1800 to 2199. For other asteroids, a Celestia developer forum shows how to how to request an SPK from HORIZONS's telnet interface. However, they appear to use the SPK for ephemeris only, adding albedo in Celestia's own SSC file ...

2

There will be a relationship but not a simple one. If we model a uniform slab of material by a complex dielectric constant $n + ik$ then we can calculate three things; reflection, absorption and transmission. If we model a dust particle as a uniform sphere of the same, then the far field electric amplitude scattered from an incident plane wave on it will ...

2

The obvious answer is: "of course". Different colour simply means different wavelength-dependent reflection; different brightness means different wavelength-independent reflection. Earth and moon have different colours when viewed from space. The real question is by how much does it differ as a function of wavelength. There are already here nice ...

1

Essentially the amount of radiation reflected per spectrum band (UV, X, visible etc.) depends on atmospheric and object surface chemical composition. In the case of the Moon you have no atmosphere, so this is already a great difference with respect to Earth. But since there's also a different surface composition between Earth and Moon you can't say a priori: ...

1

Here is how I understand these terms. Apparent magnitude is what you can see, or measure from where you really are and where the object really is. Absolute magnitude is a mathematical prediction based on a standardized distance and configuration (see below) so that you don't have to specify the particular conditions. Venus always has roughly the same ...

1

This is a long-standing (and complicated!) problem in modeling eclipsing binary light curves. Here’s a full review from 1985 (with later citations here), which suggests (from a very quick skim) that an albedo of about 0.5 has been found for some systems, but the details depend also on temperature and wavelength. For the current state of the art in modeling ...

1

Complementing @KenG's answer, Here's an actual datapoint. The new paper in Nature Polarized reflected light from the Spica binary system (downloadable here) is notable in that the measurement of the polarized component of the reflected light speaks to it being an actual reflection, rather than one star heating the other producing a more brightly radiating ...

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