# All Questions

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### Gravitational pull needed to keep a gas in atmosphere

How can you determine the gravitational force needed to keep a particular gas in the atmosphere of a planet (for example, carbon dioxide (CO2))? I came across the following formula ...
704 views

### How much of the Milky Way is visible to the naked eye from earth?

When we see the Milky Way on a dark night are we seeing the bulk of the galaxy, or just our local arm? How much of the milky way is visible to the naked eye on a dark night?
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### average number of exoplanets in a system

I was just wondering what the normal amount of planets is in a star system, because in my mind 8 planets seems like a relatively large amount. so are we above average? can we even see all the ...
20 views

I have, for years, been an Astronomy and physics nerd. For the first while, I was a total astronomy nerd. Then I slowly transitioned into physics and have been, for less than a year, a physics nerd. ...
145 views

### 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 ...
5k views

### Why there is no smoke around the Sun?

Where there is fire, there is always smoke. So why there isn't any smoke near the Sun?
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### How to convert horizontal coordinates using NOVAS?

I'm using NOVAS 3.1. I know that I can convert equatorial coordinates to horizontal coordinates using the equ2hor function. Is it possible to make NOVAS do the ...
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### SN1604, Former and Current Name of the Constellation Serphens

Kepler wrote 'De Stella nova in pede Serpentarii' describing the supernova of 1604, now known as SN1604. My understanding is that the constellations used by Kepler and the constellations used today ...
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### What were the challenges for the ancients to observe the orbit of the Moon (instead of Mars)?

Astrophysics can be said to have been founded by Johannes Kepler around the year 1600. He based his break-through science on data of the position of Mars in the sky and disproved the ancient ideas ...
179 views

### 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 sense that inside the planet region there is not ...
121 views

### What is the Northernmost Latitude of Saturn?

My wife and I were watching a TV show last night, which takes place in Salem, Massachusetts circa 1693. One character went to a particular place in the woods at a particular time to be exactly under ...
17 views

### Gravitational waves detector arm length and GW wavelength

What is the relation between the arm length of gravitational wave detectors and the wavelength of target gravitational waves? For example, LIGO detector has 4 km arms and detects waves with 10^2-10^4 ...
92 views

### 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 ...
135 views

### Mars night sky - how many stars visible?

How would the night sky look like from the Martian surface? Would there be more stars visible or less (compared to Earth)? Would they appear brighter/dimmer/same?
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### Why solar eclipse paths are symmetrical?

Reading upon the eclipse of March 20, 2015, I stumbled upon this page: http://www.timeanddate.com/eclipse/list-solar.html. What caught my eye is that for each year there are two eclipses whose paths ...
37 views

### .2015: When last did both New/Full moon in a fort-night cause an Eclipse?

Going through http://earthsky.org/…/dates-of-next-lunar-and-solar-eclipses I made the (what was for me - momentous) discovery that March 20, 2015 - New moon - is a Solar Eclipse, and that the ...
70 views

### How to learn data analysis for radio telescope?

I have done some research about Radio Astronomy to build a radio telescope with a number of arrays. I have read one of the prerequisites of working with radio telescope is a good knowledge about ...
299 views

### Naming of the planets of the solar system

Planets of the solar system have been named with Roman mythology gods names. I have a few questions on my mind concerning that subject for a while: Who decided to name them like this? When did the ...
96 views

### What kind of telescope do I need to see most of the Jupiter's moons?

I have a simple Newtonian reflector telescope. Using it, I am able to see the Galilean moons of Jupiter. However, Jupiter has much more moons than that (Wikipedia says 67 have been discovered this ...
172 views

### Sky view from Stellarium software vs. Sky view with naked eye

I'm slowly starting to interest in astronomy. Currently I'm enjoying in stargazing but unfortunately place where I live is very light polluted. I'm planing my vacation in a couple of months and one ...
67 views

### How rare are earth-like solar eclipses?

Solar eclipses on the earth are so spectacular because the moon has roughly the same size as the sun when viewed from the earth's surface. This is an incredible coincidence, and my guess is that it is ...
138 views

### Is stacking welder's glasses a safe way to watch at the eclipse?

You can find in many place on the Internet that welder's glass #14 is good for looking at an eclipse. Tomorrow (March, 20th 2015 at 10:45 CET) there's a solar eclipse and yesterday I could only find ...
60 views

### Is starquake unique to neutron star?

I read from somewhere that astronomer use X-ray to observe the "shaking" not to be confused with wobbling of a distant neutron star, I think it is similar to what geologist using microphone to ...
390 views

### Does our sun/solar system orbit around any other celestial objects? [duplicate]

Does our solar system orbit around another massive celestial object? Like a massive star or black hole for instance? From my understanding our sun rotates around the centre of our galaxy, thus our ...
33 views

### Mass resolution

Can someone define mass resolution in terms of cosmological simulations such as the millennium simulation? Is it just the smallest mass that a dark mater particle can have and still be detected by the ...
3k views

### Why did Venus not lose its atmosphere without magnetic field?

It is often stated that the magnetosphere not only shields the planet from cosmic radiation, but also prevents atmosphere loss. Why did then Venus not lose most of its atmosphere if it doesn't have a ...
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### Was the cosmic microwave background (CMB) radiation originally gamma rays?

I believe that sometime after Big Bang the entire universe was filled with high energy particles. Now we fast forward to the present; most of these particles still linger and managed to avoid being ...
383 views

### Where does energy at the beginning of a star's lifecycle (before any nuclear reactions) come from?

David Christian's Maps of Time has this to say about the period during which the first stars started to form from the diffuse clouds of hydrogen and helium that then made up the universe: Under ...
152 views

### How do astronomer measures the size of any celestial objects?

What techniques and tools are available to the astronomers to measure the size of any celestial objects such as, stars or perhaps black holes that doesn't emit light nor reflects starlight?
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### What triggers solar flares?

The sun is a big ball of hot plasma which contains free electrons. However, how does the absence of metallic elements in the sun generate the magnetic field to orchestrate these free electrons to ...
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### Do astronomers and astrophysicists more often use diameters or radii when discussing about planets, dwarf planets, exoplanets and stars?

Mathematicians much more often use radii over diameters when discussing about circles and spheres, because in mathematics the radius is more fundamental than the diameter (the sphere is defined using ...
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### What came first: the Sun shining or the existence of helium?

This seems to be a chicken and egg problem, the sun begins shining due to hydrogen becoming helium, but it's odd that there was no helium initially without the stars. Is my logic flawed? (Note: ...
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### Will the Universe end by time stopping?

I know there are several theories as to how the universe might end, if it does. Is it possible for it to end by time stopping? A friend of mine told me about this theory, but her explanation that it ...
573 views

### How many arms does the Milky Way galaxy have?

How many arms does the Milky Way galaxy have and how is it determined?
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### Shadows of Light = Space or Dark Matter?

Perhaps my title is misleading. but here is my understanding and I'm looking for confirmation. You cannot have dark without light. The only thing faster than light is darkness (i.e. shadows) Stars ...
293 views

### 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 ...
83 views

### What type of star does theory predict should be the most massive?

The most massive known stars are Wolf-Rayet stars. However, as Wolf-Rayet stars do not appear to be the first stage of any star's lifecycle, I infer that whatever these Wolf-Rayet stars used to be ...
51 views

### How does one measure velocities of far-off, bright objects

As the title already says, I want to know how one measures velocities of far-off, bright objects, e.g. when the mean parallax drift isn't measurable with current apparatus (this means when there is ...
36 views

### Simulation packages or theory to work with gravitational collapse of massive molecular clouds?

So, I am getting interested in gravitational collapse of large molecular clouds that fragment and collapse into multiple stars. Are there well-known popular academic simulation packages that simulate ...
156 views

### In theory, is there anywhere in the universe where velocity=0?

Earth is traveling at a certain velocity. Earth orbits the Sun at velocity X. The sun is orbiting the center of our galaxy at velocity Y. The galaxy is orbiting (something?) at velocity Z. On and ...
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### What do cosmologists mean when they talk about “the running of the spectral index”?

All I know is that the spectral index is related to the CMB, and that it has to be slightly less than 1 to favor inflation.
71 views

### What will the mass of the new galaxy be?

When the Milky Way galaxy collides with the Andromeda galaxy, what will the mass and volume of the new galaxy be?
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### axial tilt of uranus [duplicate]

Simple question: I read that the axial tilt of Uranus is 97.77 degrees. I don't understand why it would be this instead of 82.23 degrees the other way. It seems like saying that the Earth's axial tilt ...
98 views

### Why do astronomers use supernova to measure distance in space?

Why can't the distances between our Sun and the celestial objects be measured directly and instead had to rely on looking around for supernova? Is these events frequent, evenly distributed and lasting ...
38 views

### North Pole Right Ascension/Declination to axial tilt conversion

Wikipedia , on several asteroid articles, claims that right ascension and declination of the North Pole can give you the axial tilt of the object. What formula is used to convert these 2 values into ...
63 views

### Why are the high density regions in outer space black holes?

The escape velocity of an object is given by the following formula. $$v_e=\sqrt{\frac{2GM}{r}}=\sqrt{\frac{2 \mu}{r}}= \sqrt{2gr}$$ As far as I am aware, the mass of the star which formed the black ...
100 views

### Is dark energy evenly spaced throughout Universe?

Are there certain parts of the Universe that are expanding faster than others? Is there anyway to definitively measure this?
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### Is there a connection between black holes and dark matter/energy?

Is there a spatial or gravitational relationship between black holes and dark matter/energy?