# All Questions

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### How to Calculate Parallax Angle [duplicate]

I understand that parallax "is a displacement or difference in the apparent position of an object viewed along two different lines of sight" - Wikipedia. So, when calculating the distance from the ...
38 views

### UTC to UT1 time corrections

Astronomic observations in geodesy. It is well understood that sun and star positions may be expressed in Greenwich hour angle and declination. Or Right Ascension Declination. And may be published ...
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### DUT time offsets to UTC [duplicate]

Astronomic observations in geodesy. It is well understood that sun and star positions may be expressed in Greenwich hour angle and declination. Or Right Ascension Declination. And may be published ...
64 views

### Tripod mount missing!

I have received a new Celestron Powerseeker 127 (a 5' short Newtonian), however it came without a tripod mount. Ideas or suggestions on how to procure the right mount our a suitable alternative ...
139 views

### Do stars tend to fuse all hydrogen even when the mass is small?

Suppose a brown dwarf requires only one more hydrogen atom to become massive enough to start fusion, what will happen if we add a hydrogen atom to it? It fuses until the mass is dropped and then ...
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### Is our sun part of a triple star system with sirius binary? [duplicate]

What if our sun is not a solitary star exception? Pluto turns around the Sun, but from Pluto the Sun is very small. Idem, the Sun could turn around a very big and very far star looking very small ...
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### Moving-Cluster method for determination of the distance of Hyades. A starter problem

I am currently following a class of observational astronomy lab. I will present a brief description of the method in first and then proceed to the question, so anyone is welcomed to read the entire ...
108 views

### Why did Mercury not appear to transit through the middle of the sun?

Why did Mercury not appear to transit through the middle of the sun (the equator)? I initially thought that this was because of the ecliptic, but, then I thought that actually we'd see it above the ...
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We have discovered about 2500 radio pulsars. Part of them show pulsations in other bands like X-ray and gamma ray. The radiation mechanism remains unclear now. I wonder whether there are radio ...
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### Topography / elevation data of Mars

For a design project I'm looking for elevation data for Mars' surface - the idea is to replicate a surface area of Mars as a physical model, using the elevation data to create a very rough 3d model of ...
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### How many stars are there in a Globular Cluster of 10^5 solar masses?

I was wondering whether there is an easy way to approximate the number of stars in a Globular Cluster (GC) with 10^5 solar masses. Can one, for instance just assume the GC is made of sun-like stars ...
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### How can we explain high redshift numbers?

I just finished an introductory astrophysics course$^1$ and I have a lingering question that I can't seem to resolve. We learned that for the first few hundred million years, the universe was pretty ...
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### Likelihood of extra planets in systems identified by Kepler?

Kepler has found some systems with multiple planets and shown that it's likely that 7% of sun-like stars have Earth-like planets (video). I don't think we know enough about extra solar planets to ...
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### Why was the size of the solar system not defined by Mercury Transits?

The first measurements of the (absolute) size of the solar system was made using the Transit of Venus, an event that arguably will only happen twice in a lifetime. Transits of Mercury occur far more ...
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### What would the night sky look like if the interstellar medium didn't exist to absorb or block light?

I was curious about how much brighter it would be and how much further we could see.
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### Redshift to calculate age of stars

In multiple articles I have seen the age of a star, within the milky way, referred to as its redshift (typically denoted by $z$). I know that $z$ can be calculated as \$z=\frac{\lambda_{obsv} - ...
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### LLR & Orbital Motion

As I understand it, light that is emitted from a source is not imparted with the motion of the source and so always follows a "straight line". If this is correct, I am having a difficult time ...
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### Why aren't all planets in the same plane?

Obviously all planets are not in same perfect plane. Because if at all they were in the exact same plane, it would mean that Mercury transits and Venus transits would not be that rare. Any ...
293 views

### Do all the stars visible to the naked eye belong to Milky Way?

It is surprising that even late in 1920, people do not know there are galaxies besides the Milky Way. Does this mean that all the stars visible to the naked eye are near to us?
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### Intuitive explanation for why the universe is flat

I went through Prof. Hitoshi Murayama's online lecture where he describes why the universe is flat. One of the evidences for a flat universe is the evenness of CMB radiation on all directions. My ...
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### Would a telescope that uses Fresnel lenses be more practical than using regular lenses?

If we were to make telescopes with Fresnel lenses instead of regular lenses, would it be more practical? Would this also allow for much bigger telescopes to be made? Here is an example of the type ...
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### General question on Solar Eclipse

Let's assume 'solar eclipse' occurred Now, at what degree 'moon' will be in 'with reference to' earth (and) at what degree 'moon' will be in 'with reference to' sun In other words, by 'how many ...
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### What visible star is closest to the ecliptic?

If we were to project the ecliptic out as an infinite plane, what visible star (besides the sun) would lie closest to it?
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### Metalicity and age of bulge stars vs halo [duplicate]

From what I understand of current models, the bulge of the galaxy formed first, and thus, would contain older population II like stars. Currently, however, the halo has a higher population of stars ...
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### Chemical reactions in white dwarf and carbon allotropes

White dwarfs consists mostly of carbon and oxygen. In my opinion, they are too hot to contain these elements in molecular form and hence chemical reactions does not happen (I think resulting CO2 will ...
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### Calculating Orbital Period

I was using this formula to calculate the orbital period of a satellite in days: T = sqrt[(4*pi^2)*R^3/GM-center] Where R^3 is the radius of the orbit, or distance of the semi-major axis, G is ...
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### Why (actually) aren't ground-based observatories using adaptive optics for visible wavelengths?

Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing. The atmospheric effects are quite ...
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### Are we made of stars we're seeing? [duplicate]

a fresh astronomy enthusiast here. Recently I've been reading upon how immensely far other stars are from our solar system and how is it possible that we may be seeing stars that are already dead. My ...
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### Is it possible for the Sun and the Moon to crash into each other? [closed]

Is it possible for the Sun and the Moon to crash into each other? If yes, under what conditions? If no, why?
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### Can dark matter be explained by a nearby universe? [duplicate]

There is a conjecture in string theory wich says that dark matter is the result of a nearby universe. Suppose we live, to make things imaginable, in a line on a very small cylinder, then on the other ...
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### Calculating orbits for beginners [migrated]

I'm a game developer, and I'm working a space game, where I have to simulate a spacecraft's orbit, traveling from the earth to the moon. I would need the apoasis and periapsis of the orbit. I have the ...
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### Was NASA's moon mission completely fake? [closed]

I really want to know whether NASA's Moon mission really was a hoax, or if it is a fact. Since there are many points and scenarios which proves it as being filmed in a film studio with controlled ...
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### Why weren't the Hubble light-echo images of V838 Monocerotis supplemented by ground telescopes?

Drawing from this answer The V838 Monocerotis expansion (not a supernova) and the observation of the subsequent "spectacular" light echo was quite a notable event! From Nature 422, 405-408 (27 ...
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### Does a self-gravitating gas necessarily develop turbulence?

Though we may still doubt the exact driving mechanism of turbulence in each particular case (ISM, MC, circum-BH/-stellar discs, atmospheres...), can I say that in a sphere of dark matter particles no ...
84 views

### Solar Elevation Angles — Anomaly?

"The solar elevation angle is the altitude of the sun, the angle between the horizon and the centre of the sun's disc." - Wikipedia The meridian is when the sun is directly facing earth and is at ...
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### conditions of the early universe and inflation [duplicate]

According to our current understandings (The Inflation Theory) when the universe initially expanded it pushed space and time outward from a point. So if anything was present in the space at that ...
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### When was the nearest star discovered? [closed]

When historically did we realize that the Sun is a star, like all the others? An answer was posted, then the question was put on hold. I would like to answer: If indeed someone asserted that the Sun ...
43 views

### Why Free-Free emission is regarded as Thermal emission?

I read that thermal emission/radiation are the ones whose spectra is similar to that of a Black body radiation. Also thermal radiation depends solely on the temperature of the object. How can we ...
34 views

### How to calculate the pixel size and beam size of an image?

I have an image with some sources in it. I need to get the pixel size and beam size of that image. How can I calculate it?
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### Which frequency should be used to communicate with a cube satellite?

I am trying to build a cube satellite using a raspberry Pi. I am trying to figure out which radio frequency could be used to communicate with the cube sat to transfer data like images, videos, ...
45 views

### Why did time progress past the singularity?

I hope this doesn't sound stupid but I've always wondered: Why didn't time stop with the singularity before the big bang? I might be mistaken but doesn't time slow in proportion to the distortion of ...
118 views

### What is the first recorded reference to the Moon being a satellite of the Earth?

I saw a list recently of the moons of the various planets and the discoverer(s) and date of discovery. Earth's Moon was listed as Unknown. I know you don't 'discover' a huge disc in the sky. But ...
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### Why do post main sequence stars enter the red giants branch?

I am an early graduate student in astronomy and have hard time understanding why do post-MS stars move up the RGB. Here is what I understand about post main sequence evolution of stars. As their ...
119 views

### Why can't neutron stars ignite and explode?

Beyond the Chandrasekhar limit, white dwarfs become extremely hot. As a result, previously unfusable carbon can become fusable, causing nuclear reactions. This leads to thermal runaway and ultimately ...
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### How to calculate the LST of an astronomical object at a given height above the horizon [in degrees]?

My situation: I want to observe M52 at RA = 23h24m48s, DEC = +61deg35arcmin36arcsec from, let's say, Calar Alto at 37.23deg N and 2.546deg W. How can I calculate the Local Sidereal Time (LST) at ...
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I am currently self teaching myself some basic astronomy. My book claims, if a constellation is observed for exactly 6 months during a year, then it lies on the celestial equator. I have failed to ...
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### How to interpret extreme ultraviolet/ x-ray data in the literature?

I am interested in a sun-like star 138 light years away that is in the EUVE catalog. A table shows that a photon count of 2.6+/-0.5 photons per kilosecond at 100 angstroms has been detected for this ...
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### Why dust is optically thin in Far Infrared wavelengths?

What is the actual meaning of the statement 'Dust is optically thin in the Far Infrared (FIR) over most of the Galaxy'? Kindly Help