# All Questions

208 views

### Point Spread Function size: Full Width Half Maximum (FWHM) vs Sigma

I having been studying some astronomy papers related to galaxy observations and I realized that every time they want to express the size of the Point Spread Function (PSF) of a system which can be ...
240 views

### Could light be dark matter?

Is it possible that light itself is dark matter? I am speaking of photons (e.g. visible light, infrared, ultraviolet, etc...). I realize light is understood to be massless, but it is obvious it at ...
63 views

### Why do rocks on other solar system bodies that have an atmosphere seem to be flat?

Images taken by landers on Titan and Venus and Mars show landscapes where rocks, to me at least, are surprisingly flat. Being used to walking around in forests with roundish meter sized boulders, I'd ...
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### Speed comparison of both voyagers

I came across this page which provides (mostly extrapolated) speeds of both voyagers. Assuming they are fairly accurate, any reason why the speed of Voyager 2 (5-6 km/sec) is less than that of Voyager ...
92 views

### Why doesn't this paradox disprove (some) multiverse quantum gravitational theories?

As I understand it, one theory of the multiverse is that there are an infinite number of universes separated by small distances in other (than our observable 3/4) dimensions and that gravity is weak ...
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### If the Universe is infinite, why isn't it of infinite density?

If we make the assumption that the Universe is infinite, and has an infinite number of hydrogen atoms, then why is it not of infinite density - because, under Schrodinger's wave equation the ...
32 views

### Sensitivity of calculated orbital elements to observational errors

These days, we have some very precise ways of making measurements, but I'm sure it wasn't so in Kepler's day. So I am wondering how astronomers of that time could make such accurate determinations of ...
39 views

### Invisible in visible light but visible in non-visible light?

This may be a stupid question, but I've been wondering this for a while and haven't yet found a solid answer. I'm worried the answer will be something along the lines of "of course not, you dummy" but ...
44 views

### Can the next possible ice age be projected based upon the Milankovitch cycle?

The Milankovitch cycle describes the collective effects of changes in the Earth's movements upon its climate[.] By this theory, the Earth is now experiencing an interglacial. By the theory, ...
211 views

### How many galaxies disappear beyond the Hubble Bubble horizon every year now?

The accelerating expansion of space means that the space between us and far away galaxies expands faster than light can travel through space. There is a horizon of possible observation beyond which ...
40 views

### Naive star filter visible at night in certain country

I have a HYG catalogue and I'd like to filter out stars visible at night and in Europe. Doesn't have to be exact. I was assuming that it'll be all stars with positive declination, but I wasn't sure ...
213 views

### Are there a lot of collisions between stars in the core of the galaxy?

I'm reading on Wikipedia about Halo Stars that orbit the center of the galaxy at a high inclination away from the plane of the Milky Way. It seems that at some point, these stars must dive back into ...
35 views

### Are astronomers continuously monitoring exoplanetary systems?

I'm reading many of the Wikipedia pages about exoplanets and the different methods they are using to detect them. But I wonder, it seems that the emphasis is on detecting and finding new exoplanets, ...
227 views

### Are there large underground caverns on Mars?

Scientists talk about the possibility of life underground on Mars, and I assume they are talking about microscopic life that can live in small gaps in the soil or rock. But is there any evidence that ...
88 views

### Schmidt-Cassegrain telescope

What is a Schmidt-Cassegrain (SC) telescope? We have Newtonian telescopes and also Galilean ones. How is SC telescope different from other optical telescopes? What is its construction detail and ...
82 views

### CCD in telescopes: Observation and Astro-photography

This is a Celestron CPC 800 XLT telescope. It doesn't seem to have charge-coupled device (CCD) attached. Can a CCD be attached separately to this 8" Schmidt-Cassegrain telescope even if it didn't come ...
186 views

### Help in determining the features of an unusual, fictional star system

(Hope this is the right Stack-exchange site for this question) I'm working on a sci-fi RPG campaign, set on a very atypical location. Since this is a work of fiction, there's enough room for ...
55 views

### What are the objects that are visible from a city?

I live in a light polluted city of the northern hemisphere and I would like to know what I can see with my Skywatcher BK 707AZ2. I have already seen Jupiter (and its moons), Saturn, Mars, M45, the ...
127 views

### Does mass create space?

Imagine two cubes each with the side 1 light year. One of the cubes is empty of any matter. The other cube contains a massive star. Does the cube which contains the massive star have a larger volume ...
251 views

### Burning Out Stars

In the book "A Really Short History Of Nearly Everything", I read that the larger the star is, the faster it burns itself. Whys that? Wouldn't there be more energy to burn if it's larger, and just be ...
537 views

### Percent-illumination of crescent moon and its naked-eye visibility?

What level of percent-illumination of moon (waxing crescent), given by Stellarium, is enough to make it visible with naked eye, in clear sky? thanks
301 views

### What's the likelihood of the existence of unknown elements in the Solar System?

What's the chance that there might be undiscovered chemical elements in the Solar System - either on planets or around the Sun or on asteroids of the Oort-cloud?
112 views

### Supermassive black holes at the center of galaxies

The fact is, many, if not most large galaxies have a supermassive black hole at their center. My question is why? Is it because when these galaxies were first formed supermassive black holes were ...
50 views

### Metallicity: What are the metallicity values of various galaxies?

What are the various values of metallicity of various known galaxies, like Milky Way, Large Magellanic Cloud, Small Magellanic Cloud, Andromeda and so on?
115 views

### What is the farthest object we've been able to bounce signals off of to date?

I know people bounced lasers off of Venus and Mercury in 1960s in order to test the Shapiro delay. Since then, we've developed higher power lasers and radio transmitters (Bolshakovo transmitter). ...
71 views

### What is the physics of a gas mass subject to gravity in space?

There are many formulas for atmospheric pressure on earth, but how does gas behave in free space? I am thinking about why stars form. I am guessing that the gas density will influence pressure, as ...
151 views

### Is there a flaw with the newer purposes and correlations attributed to the HR diagram? (And would a third axis of mass correct the enclosed flaw?)

When I was younger, I was looking at HR diagrams, and began to experiment with the HR diagram. I was looking at plotting different groups of stars on the HR diagram when I found RV Tauri stars. ...
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### Any cheap (<100 euro) tools for observing the lines in solar spectrum?

I am now reading the book ''The story of Helium and the Birth of Astrophysics''. I really want to observe the lines (dark or bright) in the solar spectrum. Any easily available tools for an amateur? ...
36 views

### Singularity in Laplace Method for Orbit Determination

I have a question about Laplace angle-only method for orbit determination where the line of sight vectors are being interpolated. I read somewhere that the method fails (due to a matrix being ...
191 views

### What is gravity really?

What is gravity? I want to know more than it being simply the "mysterious force" that attracts things to earth. Is it a particle, a wave, or something else entirely?
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### Formation of stars

How are stars formed? I read somewhere that when dust, gas, rocks etc come close to each other due to gravity, slowly and gradually build up a lot of pressure and form stars. If what I read is ...
233 views

### Statistically, what would the average distance of the closest black hole be?

The closest confirmed black hole is several thousand light years away from earth. Our galaxy has about 100 billion stars. I didn't find any reliable information on the black hole count of ratio versus ...
124 views

### How many new galaxies enter the observable universe each day/year/decade?

Each day light has more time to reach our eyes from distant galaxies. In one day, light travels 2.59×10^10 km. So our observable universe (assuming my simple math skills apply here and there isn't ...
63 views

### Origin of the magnetic field of neutron stars

It seems a little counter intuitive that neutron stars possess such strong magnetic fields. Its electric charge is presumably zero, so however fast it spins, it shouldn't generate any magnetic field. ...
134 views

### If an object with mass were to somehow go the speed of light, would it destroy the whole universe?

Would an object with mass traveling the speed of light destroy the whole universe because it would have infinite energy / mass? According to ...
79 views

### Dark Energy Expansion

The new Cosmos extra features mentions that at about 6,771,500,000 years ago the universe began an accelerated expansion. How do we know this? What evidence do we have for this renewed and accelerated ...
81 views

### Could dark energy be negative gravity?

Main question: Could dark energy (the mysterious accelerating expansion of the universe) be explained by "negative gravity"? "Spin off" questions: Does antimatter have negative gravity? If ...
111 views

### Any cheap (less than 100 euro) telescope for observing Jupiter? [closed]

The moon is not challenging. I would like to observe the big planets and their rings.
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### Why does Mars' experience an 'ice age' at high axis obliquity, when Earth experiences an ice age at low axis obliquity

This paper here goes into some detail about how Mars' experiences its own form of 'ice ages' on a quasi periodic basis driven by the wobbling of its axis. The main mechanism outlined is that the ...
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### What record do we have of the length of supernovas?

recently I heard an astronomer on the radio claim that the supernova we have observed in our own galaxy lasted about 6 months, while in distant galaxies they last about 7-8 months, due to relativity ...
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### How does water exist within the frost line of a star?

My supposition is that within the distance of the so called frost line around a star, water in empty space sublimates, evaporates. I further suppose that this means that vaporized water is pushed to ...
67 views

### Stars in star clusters in SMC and LMC

Is there any catalog or any paper published in any journal that lists the stars discovered under whichever star cluster of the Small Magellanic Cloud (SMC) they belong to? There is one for Large ...
135 views

### Sum of the Masses of All Moons in the Solar System

I'm looking for the total mass of the moons in the solar system in Earth Mass this would be include the 67's moons of jupiter, the 62's of saturn, the 27's Uranus and the 14's for Neptune. it's a ...
407 views

### How many stars are visible to naked eyes around Equator area?

In the best sky conditions, we can see about 44,000 stars in the sky. But what if I am located around Equator area? How many stars I can see? From what I know, the number of stars I can see should ...
59 views

### Is Mars visible from naked-eye from Michigan (47N, 88W) these days?

Is Mars visible at night sky of Michigan these days? I was trying to search for Mars from Michigan (at elevation of 30 deg and azimuth of 220 deg) around 11:45 PM with binoculars of 20x60 but didn't ...
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### Distance of extra-galactic Classical Cepheids

There have been many questions and answers about finding the distance of a star from the earth. But as I did some research on the net, I found that we have specific approaches for finding the ...
109 views

### One year on the sun [closed]

This might be a weird question, but I'll ask it anyway. If one year on earth is the time it takes for the earth to orbit around the sun, then (if it were possible for humans to survive on the sun), ...
161 views

### Is it safer to be near a star or a black hole?

If a star or black hole neared the solar system, which would do the least damage? For the sake of a good comparison, lets assume the candidate star is an "average" 5 solar mass star, and the black ...