New answers tagged

1

I think the issue you are going to have here is that the position of a star in the HR diagram - which amounts to saying what the (2 dimensional) spectral type is - does not just depend on its mass. The Vogt-Russell theorem says that the position of a star on the HR diagram depends on its mass, its composition and crucially, how its chemical elements are ...


4

What Kepler (and others before and after him) wanted to do is predict where a planet would be. To do this we need some set up: First we want a coordinate system. This is a system of axes: x, y and z, at right angles to each other. And it should be an inertial coordinate system, so Newton's laws work. This means that the axes should not be rotating. And we ...


2

Scientists (and science fiction writers) have speculated about the possbilities of life under the surfaces or on the surfaces of large moons in our solar system or large exomoons of large exoplanets in other star systems. So a good place to find any limits on the possible properties of moons that can have magnetic fields is a scientific discussion of the ...


1

Even if the moon weighed twice as much as our planet, given a rotation of 27 days it wouldn't have a major geodynamo, which is proportional to mass, rotation speed and electromagnetic constituents. It has to have higher rotation speed and a lot of iron at the core. The moon's rotation is nearly zero, or once every 27 days compared to our 24 hours. In 2010, a ...


12

Yes, the atomic hydrogen is probably mostly left over from the Big Bang. [Edited to add: Not sure how much that is true and how much present-day atomic hydrogen is the result of recombination.] And, yes, ${\rm H}_{2}$ does get dissociated by high-energy photons -- and also by cosmic rays, which can penetrate dense, dusty clouds that block most of the high-...


4

This is one of those questions that is easy to state but complicated to answer - and this won’t at all be a complete answer, but mostly a quick outline of some important factors to consider and terms you might search for in order to learn more. The question of why the interstellar medium (ISM) has the structure it does is a long-standing one, and one that a ...


3

A detached black hole is simply a black hole that is not part of a close binary pair. There are two ways that we can detect stellar mass black holes. Firstly when they are close to a star, and matter is flowing from the star into a disc around the black hole. Matter in the disc will orbit at substantial fraction of the speed of light, and friction will ...


0

I have come up with a technique to find a solution to this problem as shown in this paper A Study to Show : Jupiter : Our Next Star My 11th grade research paper 2018


3

While I couldn't find any quantitative information about views from Earth or orbit down to zero phase angle (especially since views direct from Earth are limited in phase angle due to Eclipse), this website gives an unreferenced data point suggesting Apollo astronauts observed that a zero-phase full moon is approximately 30% (0.2 magnitudes) brighter than we ...


0

A Study to Show : Jupiter : Our Next Star My 11th grade research paper 2018 Answers under - Planetary nebula, pg 8-9 Total mass of the planetary nebula formed = 0.49 M⊙ (99% hydrogen) Revisiting mass loss, pg 12 Density of CSE1 on reaching Jupiter’s Orbit after Thermal Pulse 1, pg 17


2

Using the calculator posted by Guest, I've calculated some previous close approaches going back as far as 1600. None are anywhere near the 2029 encounter where Apophis will be close to the geostationary orbit of satellites. Going back to 1600 (the limit the tool is capable of calculating for this object), the closest Apophis encounters was on April 12, 1748,...


11

Radiative energy transport continues. The point is that the radiative flux, which is proportional to $dT/dr$ can be overtaken when the temperature gradient achieves the adiabatic value and convection starts. Once convection is started, it is very efficient and the majority of energy flux will be transported by convection. Details Broadly speaking, radiative ...


6

The lunar opposition surge has been well studied, likely because we can study it in detail, we have surface samples, and so it serves as a baseline for other bodies in the solar system (as it does for many other kinds of surface studies). It is quite substantial in visible light. Probably Clementine data are the oldest-modern reference, and among others, ...


16

The JPL Small Body Database lists Apophis close approaches dating back 100 years before discovery. Three fairly close ones were: 1907-04-13, 0.029 au 1949-04-14, 0.028 au 1990-04-14, 0.033 au While it's possible to run a dynamical integrator arbitrarily far backward or forward in time, any given pos(t), vel(t) state is only a point in a cloud of ...


13

If you visit https://ssd.jpl.nasa.gov/horizons.cgi and enter Apophis as the target body (full name "99942 Apophis (2004 MN4)"), you can go to the "Time Span" link and see "Available time span for currently selected target body: 1599-Dec-12 to 2500-Dec-30" It's possible others have calculated its position beyond this time span, ...


23

You correctly state that neutrinos do not interact too often. The physical parameter describing that is the effective cross-section. So what you observe in a detector is not the neutrino itself, but secondary particles, e.g. muons. Colloquially put, you may regard anything with high mass (density) in between the neutrino source and your instrument (to detect ...


9

High energy muon neutrinos occasionally interact and produce a muon. Energy and momentum must be conserved in the process and the muon heads off in the same direction as the neutrino. The relativistic muon can then be tracked by a network of detectors which are sensitive to the Cerenkov radiation produced when muons travel faster than the speed of light in ...


2

Imagine your line as a rectangle of width $w$ and depth $d$ relative to a normalised continuum. Without scattered light, the area blocked off by the line is $wd$ and if the continuum level is normalised to 1, then the equivalent width is $wd$. Now add 5% scattered light. The height of the continuum is 1.05 (but we're going to renormalise it) and the depth ...


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