# All Questions

7,390 questions
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### Gravity on a Planet

Would it be possible to live on an Exoplanet Planet whose gravity was twice that of earth ? We would weigh double what we weigh here on Earth and as I can imagine that would cause all sorts of ...
99 views

### Line of lights moving in a straight line , with a few following

My husband and I have just seen a line of about 15 lights moving in a straight line, quite high above clouds level with a gap then 5 lights, gap, another few, gap 1, gap a few. They were moving at ...
10 views

### Could images of (very) nearby targets be recovered from the EHT data

Reading this question I was struck by the fact that the "pointing" of an interferometer is effectively done in the correlator, at least within the common field of view of all the telescopes, which is ...
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### How are pulsars detected from Earth?

This paper on Arxiv indicates that the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T). I have an EE background and it's a long story how I ended up here, but suffice it to say ...
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### Can a black hole “supernova”?

In layman terms: nothing ever escapes the pull of a black hole, not even light when a large star reaches the end of it's life you get a supernova sometimes the "remains" of these stars can turn turn ...
36 views

### Planets may repel each other in few cases

We know that when two huge black holes collide they produces gravitational waves in space time curvature. So if I am not wrong another object in space if goes in that direction during production of ...
57 views

### Is there a maximum Julian day?

I have read various discussions of the Julian day, including that on the Wikipedia, but none of these appear to define the maximum Julian day or proleptic Gregorian year in which that maximum day ...
23 views

### What maintains the high orbital eccentricity of many exo-planets near their sun?

Over the last decade we've discovered that many exoplanets not only have highly eccentric orbits, but also orbit very close to their sun. This is true of many classes of stars. I definitely have a ...
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### What constraints are there on solid material in the ice giants?

Recently there has been experimental verification of superionic water ice (suggested to be called ice XVIII, not sure if this nomenclature is official yet), which turns out to be a solid (or at ...
51 views

### How Did Early Astronomers Measure Distances?

Prior to the era of radar and other forms of radio/RF/EM ranging, what approaches, methods, and techniques did early astronomers (e.g., Kepler, Cassini, Copernicus) use to measure the distance(s) from ...
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### How would a Fast Fourier Transform Telescope work without a mirror, dish or lenses?

I recently came across a short article mentioning the idea for a telescope built without mirrors or lenses that instead uses an array of antennas and massive computing power to resolve an image. Such ...
34 views

### How much difference did the supply of “fresh” r-process elements make to the Solar System.?

In one of the answers to this question @MartinKochanski made the interesting point that the abundance of elements heavier than iron (r-process elements) in the solar system is probably due to a fairly ...
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### Why a blue spot in some hubble images of NGC 4302?

In some images with coloring like in this one: There is a noticeably bluer region in the "bottom left" of the image, and the bottom part of the galaxy on the left. Being an inexperienced galaxy ...
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### Are exoplanets which are above escape velocity of particular interest?

I was perusing the exoplanet database and looking for some of the more extreme orbits, when I happened upon HD 20782 B: http://exoplanets.org/detail/HD_20782_b Which is also listed (in two sentences)...
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### Word for blue ring around the Earth

From certain positions in outer space the Earth will appear to have a blue ring around it when the viewer is in the shadow of the Earth and sunlight is passing through the atmosphere. Here is a ...
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### What is the temperature about 10 or 15 feet below Mars' surface?

I was wondering this for a school paper I'm writing.
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### Calculation of day lengths of moons or moons of moons

Is it possible to calculate the day lengths of moons or moons of moons? If so, does the day length depend on the longitude as well as the latitude? Also, if we calculate the day length, is it possible ...
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### Can I learn astrophysics and astronomy with my basic math?

I want to learn astrophysics and astronomy, I'm very interested in it because there are many questions that popped up in my head, and really curious about things, but I'm afraid of a little bit on ...
5k views

### Are black holes spherical during merger?

I've been thinking about black holes, specifically during the final moments before two merge. I'm wondering if black holes, or I guess more specifically their event horizons, are always spherical. ...
26 views

### Calculating the range of visible Right Ascension and Declination from specific location + time

Given a specific date and time, and coordination of a location on earth, how can I calculate (myself, or using a python package) range of visible RA and Dec? For example (but I'm looking for a ...
249 views

### Why isn't Earth tidally locked to the sun?

Given that the moon has long been tidally locked with the Earth, why isn't Earth (or any of our other solar system's planets) tidally locked to the sun?
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### Could an Earth-like magnetic field protect life at exoplanet Proxima Centauri b?

I took a look at Wikipedia's page for Proxima Centauri b, the exoplanet that orbits Proxima Centauri, where it is said it is expected to receive 2000 times of stellar wind pressures than on Earth. It ...
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### How did Arecibo make radar images of ice on Mercury's poles?

How did Arecibo make radar images of ice on Mercury's poles? How were observations of the poles of Mercury geometrically possible from Earth? How was "high-resolution (1.5-km) imaging" possible from ...
71 views

### Question from a non-astronomer /non-mathematician regarding rotation speeds

I have been watching too much TV related to black holes. Most black holes are depicted with a disk of matter that spirals into the black hole. Does the mass and diameter of the disk have a bearing on ...
72 views

### How were the orbital sizes determined in ancient India? [on hold]

Rg Veda of ancient India contains a code that gives all planetary orbital information visible in the night sky. It is worth knowing the origins of our solar system and its development through the ages....
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### Extracting kinematics from stellar spectra. Why are template stellar spectra necessary?

I am trying to understand how to extract stellar velocity and velocity dispersion maps from spectral cubes, but with no success so far. To be more precise, I do not understand why people use stellar ...
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### Is there a term for asteroseismology as applied to giant planets?

Giant planets such as Jupiter have oscillations which enable analyses using the techniques of asteroseismology, for example Gaulme et al. (2011) detected global modes on Jupiter via radial velocity ...
44 views

### really fast moving star-like light [duplicate]

I don't know ANYTHING about astronomy but I know what I saw and 2 of my siblings saw it too. I initially thought it was a shooting star, but a Google search quickly made it clear that it wasn't. it ...
49 views

### Why doesn't the solar azimuth vary uniformly

For the past few dates, I've been observing the rotation of the earth around the sun and noticed that the azimuth of the sun doesn't vary uniformly throughout the day. The azimuth varies faster during ...
83 views

### Is it plausible for a planet that is positioned in the habitable area of a solar system to have little extractable metals?

I am big fan of Asimov's Foundation and I am wondering about the plausibility of some of Foundation's imagined words. According to this article Terminus was a special world with little metals: It ...
163 views

### Ludwig's star distance

Mizar and Alcor, each about 83 light-years away, have a fainter line-of-sight companion known as Ludwig's star, which was mistaken for a planet in 1722. The Wikipedia page only says it is "roughly ...
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### Given a star's mass, age, and composition, how do I calculate the rest of its properties?

If I'm given a star's starting mass, starting composition (metallicity), and its current age, How do I calculate the star's luminosity, current mass, and radius? I want to know how to do this for any ...
55 views

### Why does the number of extrasolar planets vary in different sources?

There are at least three catalogues that are counting up-to-date discovered exoplanets. What criteria do they use to count the number of planets? Every catalogue has a different count value. So at ...
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### Is Enceladus the moon with salty water?

May anyone tell me does it known if Enceladus has water and is that water salty?
39 views

### Question on dec 2013 answer to“How to measure the altitude and azimuth of a star?”

I am looking at your response to the above question. You stated: For Northern Hemisphere, a star that is crossing the North local meridian (that is, between the Zenith and the North Horizon) the ...
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### Why are Bok globules so cold?

I have recently read a bit a out Bok globules. One thing, that is repeatedly emphasised is that they are among the coldest objects in space, with a temperature of ~3 K. Why is that so? Naively, I ...
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### Relationship between Periapsis and apoapsis longitude

What is the relationship between Periapsis and Apoapsis longitude ? Are they 180° apart ? (ie) Periapsis + 180° = Apoapsis ? Related question: if apoapsis is not known, what orbital elements are ...
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### How to check what telescopes were looking at a certain portion of sky at a particular time?

I have some data that I collected from observations at a specific RA, DEC and I am trying to figure out what telescope surveys were looking at that portion of the sky at that particular time? I am ...
46 views

### Are there any estimates for the combined mass of all near earth objects (NEOs)?

I tried looking around but couldn't find any sources attempting to answer this particular question. It's obviously impossible to know the exact answer, but all I'm looking for is an estimate. My ...
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### A good definition of specific intensity?

I’m studying specific intensity for a course on astronomical instrumentation. I can’t quite get my head around the proper definition of the term. One definition I’ve found in various lecture notes / ...
87 views

### Why would tidal forces on planets become more intense when a star becomes a white dwarf?

I was puzzled by this press release by the Royal Astronomical Society: "Small, hardy planets most likely to survive death of their stars" - phys.org, May 14, 2019 Astrophysicists from the Warwick ...
27 views

### Astrophysics of Supernovae - Energy over Distance?

I need this for worldbuilding, but it is a physics question. I want to be able calculate the energy over distance from a hypernova of a variable star like Eta Carinae. Understanding what energy levels ...
25 views

### Expansion of space or constriction of length scales?

According to wikipedia, "Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale. Although ...
40 views

### Obtaining TESS input catalog (TIC) IDs for Gaia source_ids?

The TESS input catalog (TIC) "uses the GAIA DR2 catalog as a base" according to the catalog's website. The Gaia DR2 database provides source_ids for each ...
49 views

### Time taken for sun to rotate [closed]

If sun rotates with the same angular velocity of earth, how much time does it take to complete one rotation.
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### Theory of relativity [closed]

Theory of relativity states that a fabric of spacetime exists on which objects are present, creating depression according to their masses. But then how are we able to see various objects with ...
38 views

### tidaly locked celestial body in three planet system

If a Planet have 2 Moons (so suppose system of 3 bodies) and we say "One Moon is tidally locked to Planet" how can we say that it is tidally locked when Baricenter of 3 bodies has its trajectory?
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### What is the center of rotation used to determine if two bodies are tidally locked? [on hold]

Is it the barycenter, or some other point or coordinate system origin which we use to determine if two bodies are tidally locked?