New answers tagged

10

The ninth planet can absolutely be a "virtual", in the way you describe it, meaning observed data indicating the gravitational influence by an object is not actually caused by such an object. A simple visualisation of this is the case of a two-body system, where we observe two objects orbiting a common barycentre. From the observed data, one can get the ...


2

I was able to get the Cartesian orbital vectors for all the major bodies from HORIZON at the J2000 epoch only. I could extend the coverage forward thru time. It’s easy to get data overload doing this. My simulation is modeled using the Laws of Gravitation and Motion alone. This gives results that are surprisingly close to those published. Running the ...


0

Simple answer. The sun is mostly hydrogen with an atomic weight of 1. Mercury is mostly (70%) metal such as iron (with an atomic weight of 55). Iron has a head start on density. For hydrogen to equal iron in density, 55 hydrogen atoms would have to be compressed in the space of a single iron atom. This happens in the core of the sun, but not in the entire ...


2

All the other answers address the density of the sun, but I feel that none of them actually addresses the OP's misconception. OP seems to think denser material should sink, but this is not the case. Thus Pluto is denser than Uranus, but orbits further out. There is nothing strange about this. The reason is that orbital energy is conserved indefinitely ...


8

I'd say the most important answer is because the volume of stars is counted differently than for (inner) planets.For the former, most of the gas surrounding the dense core is counted. The latter don't have significant enough amounts of it. This is even more pronounced with larger stars. VY Canis Majoris: "With an average density of 0.000005 to 0.000010 ...


0

When talking about the longitude of ascending node you must be very careful to define the reference plane that you are using. As you state, due to the Earth's axial precession, the First Point of Aries moves along the ecliptic over ~26,000 years. This is because the celestial equator is slowly precessing about the ecliptic. Now, in the case of the orbital ...


19

The density of matter depends not only on its composition, but also on temperature and pressure. It's not meaningful to say that substance A is denser than substance B without specifying the conditions under which the comparison is being made. For a simple everyday example, at room temperature (and pressure) water is significantly denser than air. But ...


43

The sun isn't the same density all the way through. According to MSFC's solar interior page, the core density at the centre of the sun is a whopping 150,000 kg/m$^3$. Surrounding it the radiative zone is around 20,000 - 200 kg/m$^3$ (already less dense than water). Eventually at the edge is the convective zone - the density at the part that we see is much ...


23

Fusion inside of a star affects the sun's density (which does not happen with a planet). It produces an outward pressure that balances against the attraction of gravity, thereby reducing the density as long as the star is burning. Once a star the mass of the sun is no longer able to sustain fusion, what is left is a white dwarf which is in fact much denser ...


1

Here's a nice animation from the Washington Post:


1

As Mercury is inclined by 7 degrees relative to the orbit of the Earth (the ecliptic) at any given time it may be above the ecliptic or below. However there are two times during its orbit when it crosses the ecliptic. These are known as "nodes". A conjunction occurs when the planet is vertically above or below the sun. A superior conjunction happens when ...


3

Mercury's orbit is inclined 7 degrees relative to Earth's orbit. This drawing is exaggerated. When Mercury is "between" us and the Sun it might be below, above, or passing through the Sun's disc from our point of view. Another post from Universe Today explains this also.


6

It is indeed possible to measure the AU using transits of Mercury, and Edmund Halley tried to do just that in 1677. However, there are two advantages to a transit of Venus. The first is that during the transit, Venus is only 0.28 AU from Earth, whereas Mercury is about 0.7 AU away. This makes the parallactic effect twice as big. The second difficulty is ...



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