# All Questions

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### Magnetic fields of peculiar HgMn A type stars

Do HgMn (peculiar A type) stars really possess global magnetic fields? See, for example, this paper by Hubrig et al. from 2012.
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### Going from the second moments of an object to its ellipticities and half-light-radius

I am studying ellipticity distributions of galaxies and am having trouble moving from the second central moment matrix (covariance matrix) to properties for an object such as its half-light radius. I ...
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### How much mass will the white dwarf sun have compared to our current sun?

In 4 billion years, when our sun sheds all of it's outer gas layers and turns into a white dwarf, how much mass will the white dwarf have compared to what the sun has today? Will the planets still ...
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### Why do dark objects look white from a distance? (Moon, Ceres, but not Earth!)

What makes the Moon shine white in the sky, although it seems to be as dark as asphalt? Earth's average albedo is 3 and 4 times that of the Moon and Ceres respectively (0.37 vs 0.12 and 0.09). But ...
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### How Are Radioactive Decay Rates Influenced by Neutrinos - On Earth and Other Dense Planets

I read a science report recently that mentioned an accidental discovery where radioactive decay rates shifted slightly slower in advance ( about a day and a half) of solar storms or in sync with sun's ...
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### Does CIBER Experiment from Caltech suggest that there can be lots of stars which are not in any galaxy?

My question is about the implications of the observations recently made by the Cosmic Infrared Background Experiment, or CIBER, from Caltech. I've read at Caltech web site: "The total light ...
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### What implications does younger volcanism have on the Moon's thermal evolution?

In the paper Evidence for basaltic volcanism on the Moon within the past 100 million years (Braden et al. 2014), suggest that features such as Ina (image below) represent a far more recent age of ...
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This article from 2011 mentions simulations about the sputtering effect caused by a solar flare hitting the Moon: "We found that when this massive cloud of plasma strikes the moon, it acts like ...
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### How to calculate position of an unknown star knowing positions of some other stars from an image?

Suppose I know the coordinates (right ascension and declination) of the stars marked with red. How should I calculate the coordinates of an unknown star, marked with yellow? Searching over the web, ...
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### Wouldn't the rings of Saturn experience tidal effect?

The "Lord of the Rings" has more than 60 moons, some of which are larger than Mercury. My question is, wouldn't the ring, which is mostly comprised of rocks, experience tidal effect whenever a moon is ...
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### How Does Black Hole Evaporation Look From the Inside?

Imagine you're inside a black hole event horizon. The curvature of spacetime is such that the direction towards the singularity becomes timelike, as reverse movement becomes literally impossible. How ...
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### Total solar eclipse, supermoon, and spring equinox all happening at the same time: anything special about this?

Today (March 20, 2015) is seeing a rare combination of the spring equinox, a total solar eclipse, and a supermoon. I am wondering if there is anything special astronomically about all three of these ...
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So, I've been starting to investigate radio astronomy, and am wondering about if certain things are possible from an amateur standpoint. I was looking at this powerpoint(that discusses building a tiny ...
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### Is there a cosmic, rather than technological, upper limit to what a telescope can resolve?

Space radio interferometers could have a baseline of millions of kilometers, but is there a point where a larger baseline doesn't improve the resolution anymore because the photons observed are ...
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### Questions about a fictional binary system, and habitability

Note: Questions are at the bottom. The rest had simply been written in a format to better organize my thoughts. The formulas used to construct this fictional solar system, had been borrowed from ...
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### What is the cause of the variation from high and low mean obliquity periods of Mars?

It is reasonably well known that Mars has a greater obliquity range than Earth, due to Mars lacking a stabilising influence of a large moon. However, the Martian obliquity seems to have gone through ...
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### How to determine scalar-to-tensor ratio r from CMB polarization spectrum?

CMB polarization spectrum can tell us about the primordial scalar and tensor perturbation. By analyze B and E mode angular spectrum power spectrum and temperature power spectrum we can determine the ...
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### Mapping selenographic coordinates onto a sphere

I have a 3D rendering of the moon, which is represented as a sphere with a radius of N pixels. I also have selenographic coordinates. For example, the coordinates of the Apollo 11 landing site are ...
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### When do Mercury/Venus reach greatest elevation at sunset/twilight for a given location?

On what day does Mercury reach its greatest elevation (in degrees from the horizon) at sunset a given location? The obvious answer is the day of Mercury's greatest elongation from the Sun, but, ...
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### What are the biggest problems about the numerical, finite-element GR models?

As I know, for example the modelling of the collapse of a neutron star (to a black hole) wasn't done correctly until now. Why? Yes, I know, the Einstein Field Equations aren't really easy to solve. ...
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### Which kind of properties can we get for cosmic ray particles hitting on an optical ccd?

It is very common that we meet cosmic ray particles in optical images recorded by CCDs. You can see the "snowflakes" in the hubble images below: Generally we should remove them in order to get ...
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### Sedna, VP113 and the likelihood of the PX/Tyche/Thelistos hypotheses

Crosslisted question from http://physics.stackexchange.com/questions/131876/sedna-vp113-and-the-likelihood-of-the-px-tyche-thelistos-hypotheses The recent discoveries in exoplanetary science ...
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### Are there sufficient observational data to measure non-Newtonian perihelion advances of any Asteroid and Comet orbits?

Anomalous (i.e. not predicted from Newtonian theory) advances of the perihelion direction have been observed for many solar system planet orbits and have been accounted for by Einstein's General ...
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### Estimating the tangential and cross component of the galaxy's shear using Gnomonic projection

I would like to know how I can estimate the tangential and cross component of the galaxy's shear using Gnomonic projection of the right ascension and declination ...
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### Intrasolar planetary surface temperature change divergence from Earth

Considering the vast amount of insulating gas emitted by human activity on Earth without a coincident release on all other planets in the solar system as well as the phenomenon that planets in a solar ...
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### How exactly can the hypothetical conformal invariance of the CMB spectrum be established by analyzing tensor modes?

In the introduction of this paper at the top of p11, it is mentioned that a hypothetical enhancement of the scale invariance of the CMB spectrum to conformal invariance could potentially be ...
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### Why can primordial tensor perturbations of the CMB be ascribed to gravitational waves?

Why can primordial tensor perturbations of the CMB be ascribed to gravitational waves? Is this attribution unique, or are there other michanisms that could lead to the ecitation of tensor modes? In ...
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### need data-point: actual counts per second with APD (avalanche photodiode) detector

I'm designing a sensor system to perform specialized [astronomy and space-sciences] experiments, and need a "reality check" to support or adjust my theoretical calculations. What I need is the ...
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### What's the difference between grism and grating?

In spectroscopic observations, sometimes you meet grism, sometimes grating. Both of them could cause light dispersion, but what is the difference?
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### Was the Universe expanding before the beginning of inflation?

My point of view is that first there was the Big Bang singularity, and then the period of inflation which resulted in the observable Universe becoming many times bigger. But was the Universe expanding ...
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### If we built one hundred 3m telescopes and point them to a single star what would be the final resolution?

We'll mount all of them in a same location and connect them to each other (like VLT) so they will combined all the results and will produce some staggering images however my question is, would they be ...
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### Spectral analysis of AGN (velocity dispersion of galaxy absorption, doppler shifts)

I was wondering what parameters I need to know/measure to calculate the velocity dispersion of a galaxy, specifically an AGN. Also, I have spectra where there are blueshifted and redshifted ...
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### How long until the stars are no longer visible by the human eye due to light pollution?

I was curious to how long it will be until the stars are not able to be seen due to light pollution. I started wondering this after reading Yummie's Flash comic Knite.
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### Is there any astronomical phenomena that could emit strong radio waves with multiples of a discrete frequency?

In the New Scientist article Is this ET? Mystery of strange radio bursts from space, it is reported that several times since 2001, astronomers have detected fast radio bursts that seem to have a ...
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### Does the mass of the universe ever change?

First do we have anyway to even estimate the mass of the entire universe? And then is there any data that shows mass being gained or lost? Would we ever know if someone was playing with the til.
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### infrared telescopes, magnitude and observations

Currently 22-23mag could be the limit to make a spectrum for ground based 10m class telescopes, 21-22may may be easy for them. 4m class telescopes could handle 20mag? I am not sure. 2m could be ...
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### How can you determine the initial volume of a planet's atmosphere?

Since the surface pressure of a planet is determined by the mass of the column of gasses above it one would surmise that to determine the pressure you must know the volume and mass of the atmosphere. ...
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### Is there a simple, analytical formula for the lunar phase brightness curve?

Brightness of the lunar disk varies as a function of phase angle. This phenomenon is very well established, as is the increase in brightness at low phase angles. Is there a simple analytical formula ...
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### Lack of planets in the Oort Cloud

With the current news about the possibility of a planet in the Oort cloud, I was thinking, why is the matter in the Oort cloud distributed so? It makes sence that inside the planet region there is not ...
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### Mars night sky - stars visible

How would the night sky look like from Mars surface. Would there be more stars visible or less (compared to Earth) Would they appear brighter/dimmer/same.
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### What mechanism could have formed the Moon's Oceanus Procellarum rift-like gravity anomalies?

According to the NASA JPL web-report, Gravity Gradients Frame Oceanus Procellarum, a rift-like ring structure surrounding the Moon's Oceanus Procellarum has been detected as a gravity anomaly by the ...
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### How do the orbits of Nu Scorpii and AR Cassiopeiae work?

I apologize for the way this question is worded but I don't think I know the proper verbiage. Basically, I want to know how the stars orbit one another in the two septuple star systems. For example, ...
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### Who discovered what set of factors is responsible for visibility of celestial bodies on Earth's daytime sky?

Visibility of a celestial body on the sky during the day depends on a number of factors - if I recall correctly: the body's magnitude, Seeing, Sky brightness, and probably some others I have missed. ...
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### Angular momentum in planetary disk formation

Reading about the formation of planetary disks, one of the major problems, it seems like, is the evacuation of angular momentum. Aparently planets can't form with the amount o angular momentum the ...
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### Calculating Postition of ISS / Hubble in space

How do I calculate the positions of above satellite in space ?
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### Exoplanet Temperature Calculations

I was given an exoplanet similar in size and distance to host star to our own earth. It's orbiting a star with luminosity six times our sun, the greenhouse coefficient 0.3, bond albedo 0.3. I need to ...
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### How do I deduce my latitude and longitude from N obervations of occultations from the same place?

I think it would be an interesting exercise to measure the latiude and longitude of my house using N occultation timings. I would like to see how precisely I can measure it using that technique, and ...
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### Is Nomad data heliocentric or geocentric?

I'm wondering if the data in star catalogues are heliocentric equatorial coordinates or geocentric equatorial coordinates. Also given the distance between stars compared to the distance between the ...