Posts by HDE 226868
The simplest way to achieve this is to have the Moon be on a perfectly circular orbit that lasts twelve months and lies in Earth's orbital plane; this would mean that at each new moon, we would get...
The scenario you describe - accreting matter being expelled by radiation pressure - will occur if the object exceeds the Eddington luminosity, a limit derived from hydrostatic equilibrium based on ...
A simple answer is that the planet is on an orbit with a high inclination relative to our line of sight. The other planets in the system may appear, from our perspective, to be in line with us and ...
The density profile of a planet's atmosphere arises from two laws of physics: hydrostatic equilibrium and the ideal gas law. Put together, they require that the density $\rho(z)$ be a function of t...
Imagine an Earth-like planet orbiting a Sun-like star in the inner halo of the Milky Way. As a halo star, it will likely be somewhat metal-poor, having formed early in the life of the galaxy, but o...
This has actually been an area of intense research for decades now. Astronomers are quite interested in the distribution of stellar masses in a variety of different galaxies and clusters. The preci...
It wouldn't. The field of a magnetic dipole has a strong radial dependence; it falls off proportional to $r^{-3}$, where $r$ is the distance to the dipole. The values you list are the strengths of...
You have two questions to consider here: Can compounds required for blue atmospheres form in significant amounts on this planet, and are the temperatures right for them to condense and form clouds?...
Use low temperatures. For a given system, we can tell if degeneracy pressure is important by comparing the Fermi energy $E_F$ to the thermal energy $kT$. if $E_F\gg kT$, the gas is fully degenerat...
I agree that a possible solution would be to add in a source of high-energy ambient neutrons. Cosmic rays are a possible neutron source, at least at high enough altitudes and assuming the uranium d...
About 100 trillion years from now. The answer to your question depends on several things: When the final low-mass star forms How long it takes that star to exit the main sequence and become a wh...
You need methane, ammonia and atmospheric temperatures of $∼$150 K. The color of a giant planet depends on the type of clouds dominating its upper atmosphere. These in turn depend on the tempera...
Some simple molecules can exist in stars - but not the right ones. Contrary to popular belief, many different types of molecules can exist in stellar atmospheres, especially cool stars like red d...
We're talking hours to days. A good deal of work has been done on protoplanet-protoplanet collisions, mainly focused on testing the Giant Impact Hypothesis for the formation of the Moon. A number ...
Many stars, including the Sun, periodically display starspots, cooler areas of the surface associated with higher local concentrations of the stellar magnetic field. They can sometimes be a couple ...
It's unlikely, on the whole, for a ring system to maintain a high eccentricity on significant timescales. Dissipative collisions tend to circularize the orbits of individual particles, even if the ...
It's an interesting scenario. The major problem is that ring systems tend to be quite low-mass in comparison to their parent bodies. For example, measurements by Cassini indicate that in the case o...
Handwaving away some of the problems here, one basic one appears insurmountable: Decoherence. This is a process that involves the destruction of the superposition of a quantum system. The loss of q...
We can treat a planet as a magnetic dipole. In this case, the strength of the field scales as an inverse cube law (rather than the more familiar inverse square law), with some angular dependence. A...
No, there's no such element that would justify this sort of attempt. We have data on the composition of the Sun's photosphere, one of its outermost layers. By mass, the solar photosphere is 98.3% ...
I can see four key problems with the system as you've described it: Giant planets. The major thing that concerns me about the system is the presence of at least two gas giants. It's long been tho...
Let's assume that this student wants to begin by understanding the twin pillars of modern physics: quantum mechanics and general relativity. There are several major tools in the toolkit of anyone s...
The technique to do this is similar to that used in constructing stellar models. You know some of the properties of your object - in this case, it look like the mass and radius. You want to figure ...
While thinking about Starfish Prime's answer to the question Algae using UV light from auroras for photosynthesis, I considered the possibility of an alternate Earth which has a normal, Earth-like ...
It might be possible. We've known for around a century (since at least 1933) that ultraviolet light can inhibit photosynthesis and possibly damage photosynthetic mechanisms inside an organism. Phy...
