Wayfaring Stranger
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What makes protoplanetary disks start rotating? (Initial energy needed to rotate)
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48 votes

Two rocks placed in space with no relative motion are going to be attracted by gravity, and hit. 3 rocks, placed in space with no carefully rigged symmetry, will likely miss each other, as the ...

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Is Jupiter made entirely out of gas?
14 votes

Comet Shoemaker–Levy 9 crashed into Jupiter a few years back. As well as these molecules, emission from heavy atoms such as iron, magnesium and silicon was detected, with abundances consistent ...

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Are there lightning bolts on Mars?
13 votes

Lightning Detected on Mars, 2006 With those dust storms, it's difficult to believe that you would not get sufficient charge separation. At only a few hectopascal pressure, thunder might be hard to ...

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Is it possible to witness a star's death?
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13 votes

Naked eye nova are fairly common, several per year. Here's one. Naked eye supernova are far rarer. SN1987a in the large Magellanic cloud was naked eye visible (vid). From this list, it appears the ...

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Can you see man-made lights on the dark side of the Earth from the surface of the moon with the naked eye?
13 votes

It's highly doubtful you could see any normal light source on the surface of the earth. Using $$\text{brightness} = \frac{\text{luminosity}}{4 \pi \times \text{distance}^2}$$ (with brightness in watts,...

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How bright is it on Pluto in the middle of the day?
8 votes

These two calcs agree pretty well: The Sun's magnitude from from Pluto is -18.7 m = -18.75 magnitudes That's quite a bit brighter than a full moon, so you'd be able to read by it.

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What is the Northernmost Latitude of Saturn?
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8 votes

Salem is at 42.5° north. At the equator, the position of the sun varies by 23.5 degrees on either side of the vertical over the course of each year, due to earth's 23.5° axial tilt with respect to the ...

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Visibility of Apollo 11 module
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8 votes

No, the orbiting rocket was not visible to the naked eye. Orbiter plus lem were about 65 square meters in size, about 25 X 25 feet. At lunar distance they subtended about 0.000001 square degrees, and ...

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Is it Possible for Planetary Bodies To Exist In Close Proximity Without Adverse Effects?
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8 votes

Quick calculation of Roche limit for two identical earthlike (fluid) bodies. Roche distance is about equal to 2.44 X radius X(density1/density2)^1/3. For identical bodies the density conveniently ...

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If you lived on the far side of the Moon, how could you infer the existence of Earth?
7 votes

A body tide seismometer on the lunar far side would pick up both the solar tide, and the 20 inch body distortion produced by the earth. While "tidally locked", the moon is not in a perfectly circular ...

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What's to be gained from the New Horizons mission once it's beyond the Kuiper Belt?
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7 votes

Possible rendezvous with a Kuiper belt object and Voyager type data on the heliosphere: "We should have power until the 2030s, so we can get into the outer part of the heliosphere," says Spencer. "...

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How does Titan maintain its atmosphere?
7 votes

It's cold out by Saturn, which reduces the tendency of gases to evaporate off into space. Black body temperature of solar system objects: Earth: distance D = 1 AU (288 K) 16°C Mars: D =1.5 (232 K) -...

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What happens if gravity shuts down for only one second?
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7 votes

I expect stars would belch mightily, neutron stars and black holes would explode. Stars are only held at their steady state size by the opposed forces of gravity and radiation, so eliminating gravity ...

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What is the farthest object we've been able to bounce signals off of to date?
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7 votes

1977, Arecibo: Galilean Satellites of Jupiter: 12.6-Centimeter Radar Observations Radar echoes. 1973, 12.6 cm: Radar Observations of the rings of Saturn Content is hidden behind Elsevier's paywall, ...

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What does the Sun look like from the heliopause?
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6 votes

0.004° converts to about 14.4 arc-seconds. That's within the range typical for Mars; 5-25 arc-seconds. You'll see the sun as a point with the naked eye. Heliopause is about 14 billion miles out. ...

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Does the Milky Way belong to a Galaxy cluster
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6 votes

The Local Group contains 54 plus galaxies. Don't know that that counts as much of a cluster. Next up in scale, the Milky way is part of the Laniakea Supercluster That contains about 100,000 galaxies, ...

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What makes the Moon and Venus shine?
6 votes

The sun is an excellent source of light for all the planets and moons, although it gets a little dodgy way out near Pluto. The moon reflects about 10% of the sunlight that hits it, that's why we see ...

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Is phys.org/space-news reliable source?
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6 votes

I've been reading phys.org for years. It's right up there with physics.aps and physicsworld. All good sources that provide decent refs. Comments are often where people who like to argue, argue. ...

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Why doesn't Earth's axis change during the year?
6 votes

The changing angle between sun and moon does cause some slight nutation in the earth's axis of rotation over an 18.6 year period. In the case of the Earth, the principal sources of tidal force are ...

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Does the Moon have an aurora?
6 votes

Technically, yes, the moon does have an atmosphere that gets ionized by the sun. NASA: Is There an Atmosphere on the Moon? our moon does indeed have an atmosphere consisting of some unusual gases,...

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How can light reach us from 14 billion light years away?
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6 votes

If a star 300,000 km away from you explodes, it'll normally take the radiation from that explosion one second to start vaporizing you. If the space between you and that exploding star inflates to 2....

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How can the Advanced Composition Explorer (ACE) warn of incoming solar storms?
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6 votes

Solar flare X-rays travel at light speed, but the solar wind from CME's travels at merely 600 to 2000 kilometers per second. It's the wind that causes aurora and solar storms, depending on the ...

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Why can I see the whole moon during various non-full-moon phases?
5 votes

It's poetically called The Old Moon in the New Moon's Arms. Project Earthshine used measurements of the brightness of the non-sunlit portion of the moon to accurately determine earth's albedo: A ...

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Travelling at light speed(inside water)
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5 votes

Cherenkov radiation (Wikipedia) Cherenkov radiation, also known as Vavilov–Cherenkov radiation,[a] is electromagnetic radiation emitted when a charged particle (such as an electron) passes through ...

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How much illumination do the background stars provide?
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5 votes

Although sources go way back, the current best estimate seems to be that of Abdul Ahad from March 2004: For an observer located anywhere within the Solar System - excluding the contribution of ...

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Do NEA (Near Earth Asteroids) have minable water ice?
5 votes

Unlikely. Plugging numbers into the Stefan–Boltzmann law gives us a temperature near 273°K (0°centigrade) for bodies near earth's orbit. The exact answer for atmospherless bodies depends on albedo. ...

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Is dark energy evenly spaced throughout Universe?
5 votes

If dark energy varied by location, then plots of 1a supernova brightness vs redshift should vary depending on which direction you look in the sky. AFAIK, that's not the case. For example, although ...

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Is there any man-made satellite orbiting our moon?
5 votes

The Lunar Reconnaissance Orbiter is still up there. At a compact 2000kg, it's likely too small to see via earth based telescope. Mission Page I think the Chinese orbiter is back on earth now, but ...

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Is there a lower limit for the altitude of orbiting objects?
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5 votes

For really low orbits over an atmosphereless body, the body needs to have a uniform density. Otherwise the gravity field is not symmetric, the orbit changes shape over time, and you end up with a ...

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Can you create an orbit in a space station using balls?
4 votes

Likely the mass of the space station would distort any stable orbit. If you put your balls in another orbit, away from the station, you might get it to work, although there are still earth and lunar ...

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