# Tag Info

23

But how big is this shadow? How many kilometers is its diameter? That's a photo of the umbra and penumbra on the surface of the Earth taken from Space. It's a little distorted because it's not directly under the ISS but far off near the terminator. It's hard to pin down the size of the penumbra because it's fuzzy and fades near the edges, but if you could ...

18

Yes, and lunar occultations have proved useful in several cases. Hazard et al. 1963 used a lunar occultation to produce a high-resolution brightness profile of the now well-studied radio quasar 3C 273. Scheuer 1965 goes into a little bit of detail on general computations. A slightly different tack was taken by Vedantham et al. 2015. They were attempting to ...

17

The umbra has a well defined diameter but the size varies due to the eccentricity of the orbits of the Earth and of the Moon. The Moon may be so far away that it can't fill the solar disk at all (for instance Moon at apogee and Earth at perihelion). We can, however, theoretically determine the diameter of the shadow that the Moon casts on the Earth. The ...

12

Occulations of artificial probes has been used to investigate the ionosphere of the moon. See, for example http://adsabs.harvard.edu/full/2008MSAIS..12...53P In this technique, radio signals from the probe are monitored as the probe passes behind the moon. There is refraction from the lunar ionosphere, which can be detected indirectly, using a doppler ...

5

This is exactly how the ancient Greeks attempted to estimate the relative distances to the sun and moon. The difficulty is the angles involved are rather small Aristarchus measured the Moon-Earth-Sun angle at half moon to be 87 degrees. (or 3 degrees less than a right angle) Which implies the Sun is about 19 times further than the moon. And from this (and ...

4

It has increased in radius since the formation of the Earth-Moon system. There were eclipses since then. See Eclipse. Hyperphysics The only way you would not have (at least partial) eclipses is if the Moon's rotation were exactly synchronized so it never passed through the ecliptic plane near the favourable time.

3

My question is, then, how does the Moon's orbit manage to not have any concavity, no matter how minute, while transitioning from the full moon to the new moon positions? Isn't that not a mathematical impossibility? TL;DR answer: Because the gravitational acceleration of the Moon toward the Sun is about twice the gravitational acceleration of the Moon toward ...

3

Obviously Wayfaring Stranger is right, but it doesn't really answer why the moon shines. I mean, it's a long way away and very dim. 10% is a low albedo, and if you put a rock with 10% albedo 239,000 miles away, we wouldn't be able to see it. Or would we? The point is, the moon is a large rock. So large that its apparent angular diameter is $1/2$ a ...

3

The length of one lunar month is (on average) 29.53 days. You don't need to use sidereal days, since dates are based on a day of the sun, not of the stars. The calculation is just division So you just need to count the number of days between March 20 and June 22 etc. There are 94 days between those dates. And 94/29.53 = 3.18 lunar months. So the moon will ...

3

Probably the most reliable guide to vsop2000-p11.dat is the reference implementation vsop2000.for. The input line in question is the first of 5399 k=0 records contributing to $x$. Those are followed by 5842 k=1 records, 610 k=2 records, and so on up to k=8. Then $y$ (k=0..8) and $z$ (k=0..7) follow the same pattern. If I read the Fortran code correctly, the ...

2

The distance between the Earth and the Moon increases by roughly 4 cm per year. So when it formed, it was much closer to Earth than it is now. This means that its angular diameter, as seen from Earth, used to be larger than that of the Sun. In the future, as the Moon keeps getting further away, its angular diameter will become smaller than that of the Sun, ...

2

Zodiac signs are equal 30° divisions of the ecliptic. In the Western tropical zodiac, these are linked to the equinoxes and solstices, and named after the nearest constellations at the time Ptolemy wrote about them. The equinoxes precess westward 1.4° per century, so the signs currently lie 25° to 30° west of their namesake constellations. ...

2

The other answers are great, but if you want an handy tool to explore the next and the past eclipses, check out this super cool website! It allows you to search all the eclipses (solar and lunar + Mercury and Venus transits) for the past and the next couple of centuries. Even more interesting are the tracks of the shadows for which you can get both a ...

2

Some parts of the Lunar South pole never see sunlight: https://en.wikipedia.org/wiki/Lunar_south_pole#Craters

2

not sure about the dark side, but there are numerous other lunar features: Wikipedia Lunar Features Maybe Catena (a chain of craters) or Rima (lunar rilles)?

1

Generally contrast is reduced when you brighten up the background, be that moonlight or other light sources. In result faint objects become less visible. This is a problem for ground-based astronomy, and Rob has the details about that. It can be solved by using orbit-based observatories where you don't have atmospheric effects. However you cannot do ...

1

Imaging and spectroscopy of very faint objects, especially towards the bluer end of the spectrum. The effects of trying to subtract the background sky brightness also become more demanding if the object is extended in size or if the angular extent of sources is broadened by atmospheric turbulence (aka "seeing"). The reason that the effects are worse at the ...

1

The plural are mare is maria, so Maria might be a good name for kitten/cat, particularly given the unnamed one is a twin. Also, olivine is common mineral on the moon, as it is on earth. Olivine is generally a darker green mineral, hence its name. From this one could derive either Olive or Olivia. Other names to consider: Quacey - Scottish for moonlight ...

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