Tag Info

New answers tagged

0

Florin Andrei what evidence can you supply to charge the oldest scientific body on this planet (The Royal Society at Greenwich) to be a profit-driven media entity. Bishop, if you are asking when the 2 specific points in time match, it is true that they have a 'astronomical' infrequency to look at. But if you look at what the common terms for the definition ...


1

There is no formal set of symbols for physical quantities that is recognised by all scientists. Units on the other hand are more formally recognised, e.g. International System of Units. Authors may select their own symbols to denote specific quantities (they should, however, always specify the meaning of a symbol). On the other hand, I imagine that it will ...


1

There are a lot of instances (such as those you pointed out) in all of science and mathematics where a symbol can mean two different things. In mathematics, there's actually a good deal of this (and the article says that the list is incomplete!). Many are based on letters, although they may have deviated from the original shape in order to make a distinction ...


1

This is a duplicated question but I think it fits better into astronomy than into physics. I'll try to answer all aspects of this question including the consequences. First, is it possible? Like already pointed out it is, like Pluto and Charon. But is is it possible for bigger planets, with the size of Earth. Well we didn't find this planet system jet, but ...


5

Orbits in Schwarzschild spacetime can be described by the effective potential $$V_\text{eff} = -\frac{GM}{r} + \frac{\mathfrak{l}^2}{2r^2} - \frac{GM\mathfrak{l}^2}{c^2r^3}\text{,}$$ where $\mathfrak{l} = r^2\dot{\phi}$ is the specific angular momentum of the orbit, which is a conserved quantity. The first two terms match the form of the Newtonian effective ...


2

The two terms are used in answering different questions. Hill Sphere: given a large mass (eg Sun) and a small mass (eg Earth), can a tiny mass (eg Moon) find a stable orbit around the small mass? (If the tiny mass goes outside the Hill Sphere of the small mass, no.) SOI: given two large mass objects and a small object between them, (eg sending a probe ...


0

There is a much easier way to do this. 1) Look up the length of the solar year in earth days 2) multiply the length of the years like this: Mercury year * Venus year * Earth year * Martian year * Jovian year * Saturn year * Uranus year * Neptune year 3) Divide by 365 to get earth years. And you have a time when they will align again ...


4

Very cool question. I want to get into a little bit of detail here because otherwise there would be a one-paragraph answer, and I don't think that would cut it. So here goes. The planets in the solar systems have orbits with pretty low eccentricities (see this for more eccentricity values). At the upper end is Mercury, with an eccentricity of 0.2056. At the ...


5

Back in 1246 CE, the perihelion coincided with the December solstice. The Earth was at perihelion at 1 Jan in 2005 and will be on 6 Jan in 2096, GMT time. The drift is not monotonic, but it does progress overall throughout the centuries. Eventually, it will drift towards the March equinox and beyond, to come back to the winter solstice in around twenty ...


1

The beginning of the year (1st of January) has been chosen for historical reasons (near the winter solstice) and has absolutely nothing to do with Earth's perihelion passage. Earth's perihelion could as well have occurred on the 10th of October. That it is near the 1st of January is pure chance (see for instance a post by EarthSky). It is, therefore, not a ...


3

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 crater. NASA had trouble with this, lunar Mascons, during the Apollo era. In one case: "The Moon has no atmosphere to cause drag or heating on a spacecraft, so ...


0

This isn't necessarily a full answer to your question, but this could cover at least part of it. Have you ever heard of the Roche limit? It's the distance inside which an object cannot orbit another object because tidal forces will tear it apart. That's thought to be the reason behind the rings of the gas giants: In each case, a moon could have wandered too ...



Top 50 recent answers are included