# All Questions

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### Why, in the Solar System, all the mass seems to be concentrated at the centre?

Is this a consequence of planet formation in accretion disks ?
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### Deriving Dark Matter; specifically looking for a table of stellar rotational speed versus distance from center of galaxy to derive dark matter

I'm trying to find some data that I can use to derive dark matter (in a loosey-goosey sort of way, I won't be too rigorous). I'm helping a friend out with a final project for his astronomy course and ...
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### What is the line of light in galaxy cluster MACS J1206?

I noticed this in a thread from world building, what is the continuous line of light in MACS J1206 slightly right of center in this picture? The only thing I could think of would be the side view of a ...
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### How does radio bandwidth restrict the choice and use of science payload on interplanetary probes?

I asked a question here about returning to Earth a physical memory capsule along with soil samples, as a complement to radio operations as today. This might return a much larger amount of data ...
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### Where can I find the image of MY Camelopardalis?

In this news article,it says The image captured by the telescope at the Calar Alto Observatory in southern Spain, reveal the physical properties of each of the stars including temperature and shape. ...
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### Why are stars so far apart?

So, this is mere musing, but it seems that stars are quite extremely far apart. I tried to determine the mean distance between nearest neighbors for stars (in just our galaxy) but I'm not sure what it ...
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### How is it known that Pillars of Creation are destroyed?

We can observe Pillars of Creation with 7000 years delay, but it is destroyed only 6000 years ago. How do we know that? How the information about explosion reached the Earth before light do?
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### where is the boundary between dark night and grey night

Is there a clear cut between them? How long and how bright will the moon be for a dark night? I googled but could not find a definition for them. People just talk about them empirically?
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### Do/did the asteroids contain enough water to create Earth's oceans?

It seems from the recent Science paper by Altwegg et al (2014) that the commonly accepted source of Earth's water being the comets might not be (completely) true. Their study suggest that the water in ...
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### What implications does younger volcanism have on the Moon's thermal evolution?

In the paper Evidence for basaltic volcanism on the Moon within the past 100 million years (Braden et al. 2014), suggest that features such as Ina (image below) represent a far more recent age of ...
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### Are there stars in the first photo from space?

Wikipedia has this photo (see below) labelled "First photo from space" which was taken in 1946 from a U.S. launched German V-2 rocket. Approximately two thirds of the image is a section of the Earth ...
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### Do Pluto and Charon have unusual Langrange points?

The usual examples of Lagrange point mechanics one most commonly encounters, Sun-Earth-L# and Earth-Moon-L#, are examples of 3-body problems where 1 >> 2 >> 3 in terms of their mass. The Pluto-Charon ...
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### Lack of contact with Aliens [closed]

Lack of contact could be due to one of three things ? Interstellar space travel is just not possible . There is no other Alien Life in the Galaxy . There exists Alien life and interstellar space ...
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### What is the most oblate astronomical object known?

There are some very vast spinning objects out there. How high can the eccentricity get, or, which I think is easier to understand, how small can the ratio between the polar and equatorial diameter ...
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### Why is there a black stripe in the Hubble images of Pluto?

While reading reports about the New Horizons misson, I noticed an odd vertical, black stripe in the images of Pluto. Here is an example: Source: Hubble Discovers a Fifth Moon Orbiting Pluto ...
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### The name of a particular low extinction region

There is a region called Baade's window. I remember there is a similar region called "somebody's window", which also has a low amount of dust. Does anyone know the name?
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### Is there a star simulation software that can handle mass ejections and supernovae?

I use MESA right now to play around with stellar dynamics, but it can't do mass ejections and therefore, I can't think of a way to let the simulated stars explode as supernovae. What simulation ...
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### What are the arguments against the Feng and Gallo thin disk explanation of galactic rotation curves?

The well-known galaxy rotation problem is described here. Basically (as one moves outward from the galactic centre, $R$ increasing) the observed pattern of variation in orbital speed $V$ is very ...
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### Typical wavelength of solar flare

I read that solar flares are customarily viewed in H-alpha light, as a temporary brightening of a small portion of chromosphere. What all can be interpreted from this? Is it because, energy of the ...
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### Visibility of earth from moon during day-time of moon

Inspired by this question. I am curious whether earth, besides being nearly fixed on one place on the moon's sky, is it visible during the day-time on moon too? My understanding is that earth should ...
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### How to convert a gravitational force to speed and direction

I am doing some calculations, and I wanted to know that after using the gravity equation, $$F = G \frac{m_1m_2}{r^2}$$ if you can use $F$ and convert it into a speed, such as km/year, and also a ...
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### Voyager spacecrafts

Will the Voyager space crafts actually reach another Star System in 63,000 years? If the answer is yes, what will be powering the crafts to keep them going for so long?
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### Spectra of electromagnetic radiation emitted during solar flare

During solar flare, electromagnetic energy is released at a wide range of wavelengths but the most dominating are x-rays and extreme ultraviolet rays. Why is that intensity of these wavelengths is ...
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### Exploiting symmetry in the axisymmetric Jeans equations

I'm solving the axisymmetric Jeans equations to determine the initial conditions for an exponential disk inside an NFW halo. The density profiles of the two components are ...
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### Distance between Earth and where The Big Bang's happened? [duplicate]

The universe is around 13.8 billion years old. We know how fast the light is. We also know how fast our galaxy moving around inside observable universe. Is it possible to calculating distance ...
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### How should one rationally deal with the issue of space travelling alien civilizations?

What kind of reasoning is appropriate to understand the as of today unanswered question of whether there are (other) interstellar space travelling civilizations in the Milky Way? We have already sent ...
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### how far away could we detect that earth has life?

My guess is that life bearing planets are too far apart to be detected. I think we can only find the ones within a sphere around our planet that is 100s of light years in diameter but I suspect life ...
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### Could the Philae comet lander be recharged by laser?

Could the Philae comet lander be recharged with a laser (or possibly many lasers) from earth? My thought would be to aim one or more powerful lasers from earth at the Philae lander to recharge it ...
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### Are our 'observations' of or near a black hole affected by gravity induced time dilation?

This answer made me wonder if matter/energy/events near a black hole are viewed (by us) in a very different time frame, how might that affect our measurements? ...
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### Could discoid galaxies be expanding?

I understand that astronomers once thought that the material in the disc of a galaxy was moving around the galactic centre (where most of the mass was thought to be) in roughly circular orbits. The ...
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### How many stars can be seen naked eye from outside the atmosphere? Ho dense is the “sky” from there?

When I was 20, I went to Naxos (Greece) with friends. I was driving my car during the night on the mount Zeus (1003 meters - 3,291 ft) listening Pink Floyd. Up there we stopped the car to take a ...
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### What it would look like to observe people with a different time flows?

As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks. So Imagine two different ...
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### How bright is the full Earth during the lunar midnight?

At lunar midnight (i.e. the new moon as seen from Earth), the Earth is in its full phase with its entire disk in sunlight, and it is the brightest object in the lunar sky. How bright is it, and how ...
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### Can objects enter hydrostatic equillibrium through processes other than the influence of gravity?

Wouldn't a droplet of liquid (say water) floating around in space become spherical and "in hydrostatic equilibrium" due to surface tension but not gravity?
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### Have we detected galaxies which have red-shifted beyond the visible light range?

According to this answer it is possible for galaxies' light to move beyond the visible frequencies due to redshift: ...
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### Why can I see the whole moon during various non-full-moon phases?

Here's an image that describes the phenomenon I'm asking about. The very thin sliver to the left is of course the surface of the moon as lighted by the sun. But the rest of the moon is also faintly ...
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### Red shifting galaxies

I am an amateur astronomer please correct if any of my understandings are wrong. We all know that from the Hubble's ultra deep field image the most distant galaxies which were created shortly after ...
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### How long do planetary rings last?

I'm surprised that this question hasn't been asked before (here or on Physics), to the best of my knowledge. It's one that I might have asked when I was a bit younger, and one that I think other ...
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### Why does the distance between Sun and Earth stay the same?

Well, we all know Sun gravity , makes the Space time curvature and space pushes the earth towards the Sun. But my question is "why the distance between the Sun and Earth is Same? Earth should have ...
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### Where can I find historic rates of meteor impact events?

I have a friend that watches a lot of TV news and they have the impression that impact events are becoming more common than in recent memory. Does the evidence support or refute this? Thinking it ...
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### Can you see man-made lights on the dark side of the Earth from the surface of the moon with the naked eye?

This question is prompted from a comment on this answer: Could a person on the surface of the moon see man-made lights on the dark side of the Earth with the naked eye? If not, how much magnification ...
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### In the chromoscope, what is the X-ray source between Ophiuchus, Libra and Scorpius?

http://www.chromoscope.net/ is a nice toy. Pressing 'L' shows the constellations as guide. There's a bright X-ray source between Ophiuchus, Libra and Scorpius. In Hydrogen-Alpha there are two ...
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### How does the Earth move in the sky as seen from the Moon?

I just want to be sure I am visualizing this correctly, because it seems odd. The Moon is tidally locked to the Earth but there are wobbles to its motion due to libration. So from a point on the ...
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### Why isn't the moon dark in a solar eclipse?

In the following partial solar eclipse, the moon is "invisible" rather than being dark. By contrast, if someone stands between my view and the sun, they will appear as a dark figure instead of ...
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### Likelihood of a stable system with a dwarf planet's orbit inside that of a gas giant

I keep thinking of various planetary system configurations, and would like to know: What are the fundamental references based on Monte Carlo long-term simulation of planetary systems' evolution that ...
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### What are the nearest galaxies I can observe?

What are the nearest galaxies I can observe using my Telescope? Does it require to be out of the city lights?
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### What is “Median Stellar Mass”?

Could someone explain what is "median stellar mass" and how is it calculated? I have seen it written as: $$\log(M)$$ or as: $$\log\left(\frac{M_*}{M_{\text{Sun}}}\right)$$ but I do not ...
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### Why is carbon so rare on the Moon and on Mars?

Carbon is the fourth most common element in the universe and in the Solar system. It is about the ninth most common element in Earth's crust. It doesn't seem to be part of any of the ten most common ...