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orbiting, graviting, means only mass maters. It could be gaz, diamon, a bag of cockroach, or even a black hole, it would not change gravitational behaviors that orbits are. ( NB: yes, black hole too. Nothing different occurs in gravity as well when a star turn into blackhole. And it was attracting distant matter before exactly as well.)

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If we assume all of the rest of the planets are neutral in charge, then only the mass of the sun matters for the Solar system. The gravity between the star and planets and other objects forms the main force that maintains the rotation of smaller objects around the sun and be stable for a long time. No matter what you fill in the sun, the mass of the sun ...

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What we see from the Earth's surface with our eyes are just stars, any planets surrounding them - indeed, entire planetary systems are not visible by the naked eye. That does not mean that there aren't any planets around those stars, the exoplanets listed in this European based Exoplanet catalogue were detected using much more precise and sophisticated ...

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The only obvious scenario involves placing a moon in the L2 point of a large enough planet. All the Lagrangian points except L4 and L5 are unstable. That implies that no such arrangement can persist without active station-keeping.

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The tilt of the Earth relative to its orbit plane is definitely caused by a force: the evidence is that the tilt oscillates. Space is frictionless and so a force by a collision or a huge volcanic blast pushes the tilt in one direction and then the oscillation starts with the tile going to maximum in one direction and then back in the other direction, like a ...

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Well, yes it is possible. Earth's rotational speed is decreasing. But the decrease rate is very small. The time period is increasing at a rate of nearly 2.2 seconds/ 100,000 years. So to increase the time period from 1 day to 365 days, it will require almost 1.4x10^12 years. This is calculated assuming that the rate of increase remains same which may not be ...

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Actually, any planet $X$ can be see to transit the sun from any other planet $Y$ with a larger orbit. That being said, the frequency for which the a particular transit happens tends to decrease as the planets you choose are further away from the Sun. For example, here on Earth, the angular diameter of the Sun is about 32 arcminutes, or just slightly more ...

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The unit of illumination is the lux, lumens per square meter. What is the minimum lux required for reading? How many lux does the Sun provide at distance D? What is the minimum lux required for reading? You can plug all sorts of numbers into this depending on how good your eyes are, how big the print is, and how close you hold it to your face. I'm going ...

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Based on the information here which claims: Daylight is between $10^4$ to $2.5 \times 10^4\,\mathrm{lux}$, and 1 candle at 1 foot is $10$ lux (I'll use this as the readability limit) using the $1/r^2$ scaling yields that "daylight" will fall to $10\,\mathrm{lux}$ at somewhere between $30\,\mathrm{au}$ and $75\,\mathrm{au}$; Pluto is at around ...

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This is very rough and based on eyeballing without careful measurements: I've got a four-watt nightlight. I can read by it (not comfortably) at a distance of about a meter. The sphere of radius 1 meter has a surface area of about 12 square meters, so it appears that 1/3 of a watt per square meter will (barely) suffice for reading. The earth gets about ...

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One point, the difficulty of seeing colors in dim light is due to properties of the human vision system. Most cameras will not have the same effect and will be able to show vivid colors in even dim light (as long as the light is sufficient for imaging). But as a good guess, with accommodation, you can read (to some extent) under a full moon. The sun ...

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The difference between the observed precession rate and the calculated precession rate excluding GR is called the anomalous precession. The magnitude of the anomalous precession rate depends mostly on how close the orbit gets to the Sun because the curvature of spacetime decreases rapidly as we move away from the Sun. So we expect the anomalous precession ...

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