# Tag Info

36

Since we're talking about terminology, we need to remember that none of this really matters, outside of clarity when communicating. Still, some people tend to have rather strong opinions on it, thus confusion about how many planets are really in the solar system arises. The people The most trusted source in Astronomy would have to be the people that set ...

28

In addition to Undo's fine answer, I would like to explain a bit about the motivation behind the definition. When Eris was discovered, it turned out to be really, really similar to Pluto. This posed a bit of a quandary: should Eris be accepted as a new planet? Should it not? If not, then why keep Pluto? Most importantly, this pushed to the foreground the ...

17

Awesome question, especially since we know so little of the answer. Nobody knows for sure how the Oort Cloud formed - I'll put that out there right now - but the current hypothesis is that it was originally part of the Sun's protoplanetary disk. All of the ice and rock coalesced into small bodies - proto-comets, if you will. While these bodies were much ...

16

No, Pluto is a so called resonant trans-neptunian object; the orbital period of Pluto is almost exactly 3:2 (1.5) times that of Neptune. This means that every time Pluto nears perihelion and is therefore closest to the Sun and also closest to the orbit of Neptune, Neptune is always at a specific angle (50° according to Wikipedia) in front or behind Pluto. ...

12

The Hubble expansion has no bearing whatsoever on the length of the year. This is because the whole Milky Way galaxy (and in fact most galaxies, if not all, and even local groups) has decoupled from the Hubble flow long ago. In fact, it could only form after it decoupled. Note that M31, our sister galaxy, is in fact falling onto the Milky Way rather than ...

11

I've also heard that people in the past knew about orbits even when they thought that Earth was at the center of the solar system. How did they figure this out in their times with their technology? The same celestial objects (stars, planets, the Moon) could be seen every year. So, people figured out there was a pattern to it. At first, geocentrism was ...

11

The precise presolar history isn't known. I'll try to tell a likely story backward in time. Our sun probably has brothers and sisters scattered throughout the Milky Way. Further back in time our sun likely was part of on open star cluster like the Hyades. Open star clusters are not stable and eject stars over hundreds of millions of years. (More about ...

10

This is not a coincidence at all, but a direct consequence of the way the solar system was formed. The generally accepted model is that solar systems (including our own) form out of a Protoplanetary disc. Gravitation causes mass to collapse around a protostar, which always has some angular momentum (as does everything). Wikipedia explains it better than I ...

9

Key factors: How close is perihelion? Too close and it may be destroyed on its first pass. We know Halley's Comet, which has a perihelion of about 0.6AU, has been orbiting for over 2000 years, passing the sun every 74-76 years and is still going strong. How big is it? Every pass loses material, so a bigger comet could last longer. What is its composition? ...

9

(Disclaimer: As I already pointed out in a comment to the question above, I never did a calculation with $H_0$ before and I might be utterly, horrible wrong with my interpretation.) If you completely ignore the slowly changing orbit of earth and only take expansion of space into account and assume the Hubble-parameter to be pretty constant in the timeframe ...

9

Many models shown in books or television show a very populated asteroid belt but in fact the belt is mostly empty. To answer your question, the inclination of the asteroids vary a lot going from 0° to 40° although most off them are in between 0° and 30°; See The orbital element distributions of real and modelled asteroids. So yes it would be 3 dimensional. ...

9

On any given day, you see the moon rise in the east and (apparently) travel across the sky from your left to the right; therefore, you would assume (incorrectly) that the leading edge of the moon's movement must be to the right. That is not correct. The apparent motion you are seeing is predominantly from the Earth's ~24 hour rotation. But the orbit of ...

9

According to the Case Western Reserve University webpage The Edge of the Solar System (2006) an important consideration is that The whole concept of an "edge" is somewhat inaccurate as far as the solar system is concerned, for there is no physical boundary to it - there is no wall past which there's a sign that says, "Solar System Ends Here." There are, ...

9

All stars could have their own Oort cloud, but all stars don't. As HDE says the Oort cloud was formed by material in the sun's protoplanetary disk and interstellar comets that were caught by the sun. Some theories say that almost all comets were formed around the Sun, and this wouldn't allow us to say much about comets around other stars. However there are ...

8

Self-sufficiency is an incredibly broad term. We could argue that yes, there is water on the Moon, and that yes, there are viable ways to produce required electricity in self-sustainable ways, but the real question is, are there areas on the Moon that would be viable for both at the same time. You see, the most likely place where surface or near subsurface ...

8

Mathematically, the motion of the Pluto-Charon system can be decomposed into two parts: The motion of Pluto-Charon about the Sun, and the motion of Pluto and Charon about one another. If one sets the reference point to be the center of Pluto, the path the Pluto-Charon system would appear to follow about the Sun would be an epicycle, which is a far more ...

8

Yes, Pluto is still a dwarf planet. According to the IAU website, it still fits the criteria for a dwarf planet, fails to meet the criteria for a planet, and still carries the "dwarf planet" label, whatever its future status may be. I'm sorry I can't provide a longer or more detailed answer, but this is really a yes-or-no question. I hope this helps.

7

Few important points about WISE: it was able to detect anything with a temperature above 70-100 K, whereas the coolest brown dwarfs are in the 500-600 K range (the coolest was discovered by WISE itself, see Mainzner et al., 2011); it was able to detect objects larger than 1km up to 3 AU from the Sun, or objects of 2-3 Jupiter masses in a distance up to ...

7

The tilt of our solar system (or any star system) is determined by the net angular momentum of the gas cloud from which it formed. This might be a bit of a vague answer, but over time, the formation of stars and their respective planets is thought to look something like this: Other influences (net forces: maybe nearby massive objects, or other components ...

7

The principle is almost exactly the same as a watch or clock, but instead of three concentric axles, you need 9 for the planets. Have a google for Orrery kit - there are loads available. It is really all simple maths - you just need to know relative orbital periods in order to calculate cog sizes. (picture from curiousminds.co.uk) For moons, you do add a ...

7

As far as elements (e.g. on the periodic table) go, I would say the odds are very slim. We already discovered or produced all the elements of the Periodic Table up to atomic number 112 at least. As the number increases, the half lives of the elements generally decreases, and is very short for elements above 102. If this trend holds true as the number ...

6

Answer to the NEW question: the Angular Momentum Conservation Law states that, for any moving body, its angular momentum does not change unless you exercise an external force different from the central force. For an orbiting body like a planet, this means that Sun's gravity, being the central force, does not modify Angular Momentum, but any other external ...

6

There are several potential explanation for the cause of the late heavy bombardment. One of them includes a passing star that disturbed the Oort cloud. A "stellar system collision" would have destroyed the solar system, though. While galaxies are mostly empty and a galactic collision won't involve that many actual collisions (if any), the gravitational ...

6

The Wikipedia article for Pluto shows a low-resolution map of the surface, generated from Hubble images: And the Wikipedia article for Pluto's largest moon Charon shows a low-resolution map of the Pluto-facing side of Charon (not to scale): Larger image here. Only the Pluto-facing side is shown because the map was generated from brightness variations ...

6

In the protostar stage of the Sun, it was surrounded by a (spinning) gas cloud. This cloud behaved like a fluid (well, a gas is a fluid), so it flattened out into an accretion disk due to conservation of angular momentum. The planets eventually formed from the dust/gas in the disk from compression of the dust in the disk. This process won't end up moving the ...

6

No. From 1979 to 1999, Pluto was the eighth planet from the sun. In 1999, it slipped beyond Neptune to become the ninth. But Pluto's 248-year orbit around the sun takes it 17 degrees above and below the plane in which Neptune and the other planets travel. So their paths don't actually cross as they swap positions. Imagine you are the sun in the middle of ...

6

If you check 2001 A Space Odyssey saga, Europa is actually a satellite with Life. Coming back to real space, the "comfort zone" for life is approximately from Venus' orbit to Mars' orbit. There, only Moon, Phobos and Deimos are satellites, and all of them are too dry to have any kind of life. Beyond the comfort zone you need some other way for water not to ...

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