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4

I'll make a simplifying assumptions that the giant planets are very close to spherical and that the density inside these planets depends only on radial distance from the center of the planet. (This is not quite correct as the giant planets rotate rather quickly, making the planets oblate spheroids rather than spheres. But the differences are small.) These ...


4

That's a tricky question, if you want to go into enough detail. Generally, the gas giants consist mostly of gas, and you can derive the density and thus gravity if you know the equation of state of the gas (that's the tricky bit). A random treatise on the exploration of Saturn's internal structure based on gravity data could be this article as found in ArXiv....


-4

It could be taken at an Indoor Sky-Diving facility. These use very powerful fans to create a vertical wind-tunnel, which basically blow their customers into the air. People pay for this apparently.


69

The biggest give away is the size of this chamber: its too big for any of the known NASA's KC-135 or ZG's 727-200. That leaves us one other candidate: their Russian counterpart IL-76 MDK The interior, roof, lights, and door in the back ground is pretty much identical. (source: zeroflight.org)


2

According to an article in the NASA ADS journal, Measuring The Moon's Mass: It can be seen that the lunar mass was known to about +/- 50% between 1687 and 1755, +/- 10% between 1755 and 1830, +/- 3% between 1830 and 1900, +/- 0.15% between 1900 and 1968, and +/- 0.0001% between 1968 and the present [2002]. In 1900, the size and distance of the moon was ...


2

I think, if you assume a flat surface, nothing would physically prevent a bicycle being ridden, slowly, on Deimos. In particular friction is not a problem: friction limits the amount of force the tyres can exert on the ground, but the force you need is extremely low if the acceleration you need is extremely low, which it is. Riding a bicycle is something ...


1

This answer is really a long comment: it doesn't answer the question as such, but rather tells you some ways you probably can't measure the mass of the Moon in particular, but with an interesting corollary. One tempting thing is to say: well, the Moon's gravity should alter $g$ on Earth: can we measure that? Well, let's assume that the Moon and the Earth ...


3

Answering your first paragraph: But did Newton already calculate the Moon's gravity to be about a sixth that of Earth? His calculations were off. Principia Mathematica, volume 3, proposition XXXVII is "To find the force of the Moon to move the sea". Corollary 1 finds the ratio of the Sun's force on the tides to the Moon's force on the tides. ...


4

There are two small moons of Mars called Phobos and Deimos discovered in 1877. Using orbital mechanics the mass of Mars could be calculated from the observed orbital period and the orbit diameter of the marsian moons. Using the diameter of Mars from astronomical measurements the surface gravity could be calculated. Before the space age, the orbit diameter of ...


7

There is a nice Wikipedia article about the transit method for finding exoplanets by detection of the light intensity drop caused by the planet when passing before its central star. Unfortunately this article is available in german but not in english language. If we take the perspective of an alien astronomer searching for explanets around a star of the ...


43

A very good question! The reason is essentially to do with tides. And a slightly over-simplified summary is: If the moon orbits more slowly than the rotation of the parent body (as our Moon does, 12 degrees per day while the Earth rotates about 360 degrees per day) then the moon will gradually orbit further and further away. If the moon orbits faster than ...


10

Orbits beneath synchronous orbits have a higher angular velocity than their planets rotation, orbits above have a slower angular velocity. Drag (atmospheric or tidal) would try to match the angular velocity to the planets rotation. So below a synchronous orbit objects get slower, above it they would speed up (and slow down the rotation of the body they are ...


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