# All Questions

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### How can the Earth and the Moon be in synchronous rotation if the Moon won't be in geostationary orbit?

It is said that the Moon moves away from Earth and that during the Sun's red giant or white dwarf phase the Moon will be about 40% farther than now and in a synchronous rotation ("hantle rotation&...
15 views

### As the Moon and the Earth are predicted to get into tidal lock, how slow would the Earth rotate?

During the Sun's red giant phase or later the Earth and the Moon should be tidally locked to each other. The Earth is said to have a slower rotation then. Do we have any idea how long a sidereal day ...
36 views

### Is Neowise viewable from my position?

I have had an impossible time trying to locate this comet. My lat/long is 38.3/-82.4. My elevation is 705ft. The application that I'm using shows me exactly where Neowise is supposed to be (North East,...
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### I'd like to photograph NEOWISE from Los Angeles, what is the optimal time?

I live in Los Angeles and have a camera adapter for my telescope -- nothing fancy just an Astromaster 114. What is the optimal time, in terms of dark sky and bright comet, to take a photo of Comet ...
79 views

### How did Arecibo make radar images of ice on Mercury's poles?

update: I still haven't been able to get my hands on the Icarus paper linked below (I'll try other libraries) but these are newer and quite interesting!: Constraining the thickness of polar ice ...
50 views

### Could a near collision with small black hole account for the effects of the 9th planet?

Much interest has been raised about the existence of a 9th planet. One reason for this is the strange orbits of bodies in the outer solar system. Could the orbits be explained by a near collision of a ...
191 views

### What's the critical mass of a rocky planet before its gravity traps enough gas in its atmosphere to start becoming a gassy planet

Looking at the latest theories, I've noticed that most rocky planets are below a certain mass range. I speculate that maybe the way gas giants and gas dwarfs form is a rocky planet during the ...
720 views

### Is there a website that shows equivalent views through different telescopes?

I'm trying to buy a beginners telescope. I have a Celestron TravelScope, but would like something better. When I look at other models, many users have posted images from their viewfinders. Is there a ...
25 views

### Horizontal to Equatorial Conversion - Code

Following this tutorial I have been able to convert from Equatorial to Horizontal Coordinates and am now searching for a way to do the reverse. I understand this kind of question has been asked and ...
553 views

### Blue color of ion (plasma) comet tails

What exactly is the cause of blue light of ion (plasma) tails of comets? Somewhere I have read that the source of blue light are CO+ ions which has just acquired the missing electron and became ...
21 views

### What would I see with a telescope of 70mm aperture , 300mm focal length and maximum magnification of 150x

What would I be able to see with 70mm aperture telescope with 300mm focal length with maximum magnification of 150 x?
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### How much damage would collision with a similar mass primordial black hole do to earth?

All this talk of Planet 9 perhaps being a primordial black hole (PBH) made me wonder how dangerous a PBH collision with earth would really be. Specifically, if earth collided with a PBH of 1 earth ...
24 views

### How much of the Sun's disk must be covered for a visible shadow to be cast?

At first it seems like the answer is obvious, $100$% or more, that's what a total solar eclipse is after all. But after seeing satellite images of the June 21st 2020 annular eclipse, the shadow cast ...
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### HD 219134 b echelle spectrograph spectrum

Does anyone actually have a nice echelle spectrogram of HD 219134 b ? Everyone says they get results from APF but no one actually posts it in papers.
27 views

### How would you define “space” in GR (General Relativity) and in QFT (Quantum Field Theory)?

Is there a univocal definition of space that can be accepted in GR and in QFT? In GR space is actually "Spacetime", a 4-dimensional entity that includes time. In this case it's impossible to ...
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### Can the paper narrowing Solar System's barycentre to within 100m help find Planet Nine?

I've just read this recent news article, Astronomers Have Located The Centre of The Solar System to Within 100 Metres, reporting on a paper[1] that claims narrowing the Solar System barycentre to ...
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Can anyone tell me if the constellations have ever been in this alignment before and if they match the sign of the dragon in the book of Revelation.
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### Lucky imaging with Celestron 14 - is this result reasonable?

I attempted to do some lucky imaging of Jupiter using a permanent installation (Celestron 14" SCT + Paramount ME II) and Nikon D5600 attached directly to a Baader Hyperion 8-24mm eyepiece (...
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### Solar flares/CME dangers to life?

I know a repeat of the 1859 Carrington Event (coronal mass ejection) would pose a severe risk to power grids and telecommunication networks but wouldn't pose an immediate threat to life. If a large ...
34 views

### Galactic winds/outflows: why and how are they detected via blueshifted absorption lines in spectra?

I know that galaxies can eject gas due to supernovae, accreting black holes, etc. These galactic "winds/outflows" are often defined/detected observationally using blueshifted absorption ...
129 views

### Precision in the measurement of the distance to the Sun

How precisely can the distance to the Sun be measured? Wikipedia says the distance to the Moon can be measured upto millimeter precision. But Wikipedia article on distance to the Sun says only about ...
86 views

### On gravitational wave radiation and arrangement of galaxies post- big bang

Orbits of planets and stars decay due to gravitational wave radiation. An elliptical orbit would become more circular with time. This is especially observed well in binary systems. Taking the example ...
7k views

### Why hasn't the “9th Planet” been detected already?

In the comments to this question, there was considerable doubt placed as to the subject of if the so called "9th planet" really exists. That wasn't really the intent of the previous question, so I ask ...
140 views

### Could Planet Nine be much smaller than thought previously?

In 2016, Caltech astronomers began testing a Planet Nine hypothesis to explain the eccentric and inclined orbits of distant dwarf planets such as Sedna, 2015 TG387, Niku, and 2012 VP113. The ...
137 views

### Which kind of strategy should we take to discover Planet 9 and other KBOs?

What are the differences between the discoveries of Sedna, 2012vp 113, and the supposed Planet 9? All need deep infrared surveys at the ecliptic plane, but P9 needs a much deeper survey?
46 views

### What do these statements about interstellar magnetic fields really mean?

Quanta Magazine's The Hidden Magnetic Universe Begins to Come Into View is a fascinating review of a rapidly evolving field in astronomy. It contains some statements that I feel are important to ...
46 views

### What is the orbital velocity of Pluto around the Pluto-Charon barycenter?

I know the formula for orbital velocity but that doesn't seem of much help when I'm trying to calculate how fast the primary wobbles, or since the barycenter is outside Pluto in the Pluto-Charon ...
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### Why is the position of the Sun so fixed? [duplicate]

Please correct me if I tell something wrong. As we already know, a planet (e.g. Earth) remains on its orbit due to the gravity of the Sun. If the Sun's gravity were not there, the Earth would be ...
779 views

### Could the Sun and our Solar System one day leave our galaxy?

I have now learned that the Sun is not fixed in place, so I asked myself this question: It is possible, that the Sun and our Solar System will one day leave our galaxy? If yes, how, and if no, why not?...
53 views

### Do stars have “radio photospheres”? Are they different from their optical photospheres?

Comments below What is the maximum distance measurable with parallax? discuss challenges associated with parallax measurements of Betelgeuse and link to Wikipedia’s Betelgeuse; Distance measurements ...
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### How did Kepler come to the potencies in his Third Law?

How did Kepler come to the conclusion, that exactly the square of the period and the third potency of the great semi-axis of the ellipse is proportional? Why is only square divided by cubic = ...
49 views

### Metal lines in Lyman-alpha forest

I need to find metal lines in the Lyman-alpha forest of quasar spectra, without the red side of lyman alpha emission line. Can you guide me how to do this?
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### How to calculate the statistically significant level for a guassian line profile?

In some papers, they fit a line profile with gaussian model. For example, in this paper, fig 1 draw three gauss line profile, O VII, O VIII, and Ne IX. But the data seems noisy and the gaussian height ...
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### Why did it take five years to “figure out” how to use astrometric calibration sources to deblur LOFAR images?

Quanta Magazine's The Hidden Magnetic Universe Begins to Come Into View is a fascinating review of a rapidly evolving field in astronomy. It contains some statements: In their paper last year, van ...
1k views

### Why can’t I see any detail on planets?

I really want to know why I can’t see detail on planets. This summer my Dad and I went on a trip to Utah I went outside to look at the planets and couldn’t see detail on Mars, Saturn, and Jupiter. ...
60 views

### If I know apparent planetary positions how do I calculate the date?

I have planetary position in retrograde how do I calculate the date? For eg, I know Mars was in retrograde in Scorpion (Sidereal 210 to 240 deg), how do I calculate the date and year of this? As of ...
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### In the 1950's how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)?

In my question Why are quasars so far away that they couldn't be optically resolved in the 1950's? I included the following short paragraph, but then added strikethrough to the second sentence ...
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### Has optical interferometry been done at radio frequency using heterodyning with a laser in a nonlinear material?

If one collects narrow band optical emission from a large telescope with frequency $f_1$ and mixes it in a nonlinear crystal with laser light of a nearby frequency $f_2$, it would produce two new ...
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+200

### Examples of radio correlations over times much longer than interferometric baselines?

Very Long Baseline Interferometry or VLBI such as the Event Horizon Telescope or JPL's delta-DOR (see below) uses baselines of the order of the Earth's diameter. Spacecraft position determination ...
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+100

### What can be learned from low frequency radio astronomy available outside of Earth's ionosphere?

As discussions and answers to How large does refraction become in radioastronomy? point out, it is difficult to do radio astronomy much below 30 MHz (or 10 MHz depending on how aggressive you are in ...
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This Question and Answer got me thinking. If atmospheric seeing at visible wavelengths is the result of refractive index inhomogeneity, would it also be a similar problem for mm to cm wavelengths? ...
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### Why the earth orbits the sun from X to -X and not the opposite

I wonder all the time, why the earth orbits the sun as expected from east to west(X to -X) ? It could be different, for example from the west towards the east . What would happen if that were the case?...
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### Specutils Gaussian1D fitter and estimators

I am running the "simple example" from specutils to do some line-fitting. The demo code is here: https://specutils.readthedocs.io/en/stable/fitting.html This runs and does what it says. ...
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### What is the spectral reflectance of starlight in a close binary?

Ignore the Blender Monkey! (from here) In a close-orbiting binary pair, a small but significant fraction of the light from each star falls upon the other, and the result has to be carefully modeled ...
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### Hypothetical planet jump: Will it perturb star systems?

In a more speculative corner of SE somebody was dreaming up a story of planets traveling between star systems through wormholes. I was wondering how much the appearing/disappearing of a planet the ...
39 views

### What's the exact story of jupiter and our earth, not becoming a super-earth?

I've been watching the Cosmos documentaries by Neil DeGrass Tyson and the ones from Brian Cox, and in one episode (I don't remember from which series) there's something about the creation of the rocky ...
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### Is there an all sky meteor watch with spectroscopy?

I assume performing spectroscopy on meteors would give us information about the composition of the outer layers of meteoroids, which we can't study on finds because it has already burned up. This ...
448 views

### In what ways does the mass and energy of the milky way curve space time?

Space is curved by mass (or more precisely by mass and momentum as described by the stress-energy tensor). The milky way system has a lot of mass and a lot of energy. In what ways is space-time curved ...