# All Questions

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### Is there an orbit that could cause regular debris showers like in the movie Gravity?

[some spoilers] If you were in the ISS and orbiting the Earth roughly every 90 minutes, would it be possible for debris to be orbiting such that it passes you every 90 minutes? While Neil DeGrass ...
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### How long does it take to produce a star? Why does it take that long?

I wonder, why stars take a really long time to become stars? Is it because it needs to gain mass? Or heat up? Something like that? And could it be sped up at all?
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### Hulse Taylor Binary Pulsar - How is “Cumulative Periastron Time shift” calculated?

Following on from a previous question about the interesting Hulse Taylor Binary Pulsar. Weisberg & Taylor, 2004 present a graph showing the change in "Cumulative Periastron Time Shift" over a 30 ...
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### What should I look for in an astronomy tripod?

I have a Celstron SkyMaster 20x80 binoculars, and a tripod — Vanguard 263AT with a SBH-100 head. The binoculars weighs 2.2kg, while the head is rated to a loading capacity of 10kg, and the legs to a ...
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### How can light reach us from 14 billion light years away?

One thing that I can't quite wrap my head around is how light is traveling to Earth from 14 billion light years away, aka the beginning of the universe. The way I see it, the universe itself was very ...
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### Time after sunset until star can be seen

Given a star's apparent location and apparent magnitude, how how many degrees below the horizon must the sun be for the star to be visible to the naked eye for an observer on Earth at a specified ...
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### how did James Bradley discover light aberration?

I do not understand his timing method. James The magnitude of the aberration could be v/c? The speed of earth is about ...
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### how does redshift prove expansion is accelerating?

My astronomy teachers never would answer this for me... Redshift obviously indicates an object (such as another galaxy) is moving away, but how do we know its acceleration from this? It's my ...
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### 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 ...
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### 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). ...
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### 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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### 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 ...
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### 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 ...
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### Average amount of annual daylight at any place on earth

If this is the wrong group please direct me to the correct one. It seems intuitively obvious that the amount of daylight per annum should be the same for any latitude on earth. For example, 12 hours ...
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### What is the optimal escape trajectory from near a black hole?

Consider a space ship that is being drawn closer to a black hole. The crew begins to notice the effects, and discovers that they are nearing the black hole. They then manage to halt their ...
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### How does solar activity (e.g. flares, coronal mass ejections) change over the life cycle of a Sun-like star?

As a Sun-like star is born from a collapsed nebula and generates energy by nuclear fusion some of that energy is converted to magnetic fields which fuel solar activity. How does that activity evolve ...
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### Motion of the sun as observed from mercury

I recently found this animation which shows the motion of sun as observed from mercury. It seems as if the sun stops in between, retraces a bit and then continues towards the west. What is the reason ...
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### What determines which frequency range a radio telescope has?

My simple understanding is that a parabolic dish focuses radio waves to a receiver. It is obvious that any parabola focuses visible light and heat, so I assume that it focuses all radio wavelengths ...
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### What mechanism causes oscillations of the solar system's orbit about the galactic plane?

In a recent paper (news release here) Lisa Randall and Matthew Reece propose that a dark matter disk coinciding with the galactic plane together with the solar system's oscillations through the ...
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### Apogalacticon and Perigalacticon

What is the length of the apogalacticon and perigalacticon of the Sun and Milky Way? The general terms seem to be apoapsis and periapsis. My greatest efforts at Googling have failed miserably. If ...
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### How can I calculate the orbital periods in a binary star system?

I have two stars, with known masses and known orbital radius. How do I calculate the orbital periods of both stars?
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### How many earth-like planets do we know at this moment?

Well, the title says everything... How many earth-like planets have we discovered out there? Discard too big (made of gas), too cold, too hot, etc. Consider earth-like sun distance, size, temperature, ...
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### What's the estimated remaining life of Halley's Comet?

I know that Halley's comet is seen from Earth every 76 years or so since a couple centuries. As it travels, and particularly when it comes near the sun, it loses some of its material (ice). Someday, ...
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### Can orbital migration cause a planet to crash into the sun?

If the planets move out of their current orbits into other orbits over long periods of time could this cause a planet to crash into the sun? Maybe the term crash is a little dramatic, could the orbit ...
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### Motion of rogue planets

Two Questions: 1) Are rogue planets in motion, i.e. are they just wandering freely in space or stationary? 1) Do rogue planets have defined path or a one which can be anticipated? I understand that ...
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### Recommended papers

I am highly interested in how the moon originated. Theories suggest that the moon is a chunk of the earth, or rather, both were at one point one celestial body. Is there any literature out there with ...
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### Does gravity propagate?

Gravity is sometimes described as a curvature in space-time. Due to relativity, doesn't this imply that gravity doesn't propagate? A thought experiment. If you are moving toward a black hole, this ...
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### Internet Resource which register all Ultra-long Gamma-Ray Bursts

I read in a scientific magazine there was new gamma bursts that last longer than usual. One was detected during december 2010, also known as Christmas Burst: GRB 101225A and another one in 9th of ...
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### How to calculate Longitude from Right Ascension?

Considering that a star of certain declination is crossing the local meridian at the observer's zenith at an unknown location on the earth. Here, the declination of the star is equal to the observer's ...
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### Periodic error correction in automatic telescopes

I am starting a study on automatic telescopes and the correction of their periodic error. I found two ways of correcting it : with a CCD camera and manually by recording the error. I was wondering if ...
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### Which galaxy is receding from the Milky the fastest? What is known of the mechanism behind its recession?

Galaxies are always in motion relative to the Milky Way, my question is, which galaxy is receding the fastest from our viewpoint? What is the theorised mechanism that causes this?
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### Evidence behind Giant Impact hypthesis

The giant impact hypothesis is a theory to explain how the moon was formed. What evidence is there that supports the theory and led us to find the current theory?
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### Hypothetical scenario, two nearby black holes

I've always wondered what would happen if a hypothetical scenario, two black holes meet, with similar proportions: Maybe one swallow the other one? Or would make a bigger one between them.
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### How did the Hulse-Taylor Pulsar Provide Confirming Evidence of General Relativity?

What measurements and observations of the Hulse-Taylor Pulsar agreed precisely with the predictions of general relativity, and how did these measurements support the theory?
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### How did the reionization epoch make the universe “transparent”?

I've been reading about the reionization epoch of the universe, and it isn't entirely clear to me. As I understand it, very shortly after the big bang the universe was ionized, with the electrons ...
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### Compute Planet's Apparent Visual Magnitude

In a hypothetical solar system there exist: a sun of radius $r_s$ and absolute visual magnitude $V$ the Earth, with radius $r_e$ and distance from the sun of $1\,AU$ another planet, wit radius ...
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### Classification of a Comet

Google's definition of a comet is: a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun. This ...
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### Is the expansion accelerating or Decelerating?

According to Hubble's Law, the farther a galaxy is, the farther it is moving away. But do we take into account the fact that we are actually looking in the past? For example, there are two galaxies A ...
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### Does Tobler's First Law of Geography Apply to Star Composition?

There is a principle in Geography called Tobler's First Law of Geography which states that "Everything is related to everything else, but near things are more related than distant things." Does this ...
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### Instrument aperture sizes on Hubble Telescope

When looking at the diagram of the focal plane of the Hubble Space Telescope I noticed that the aperture sizes of most of the scientific instruments are very small. They occupy a very tiny fraction of ...
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### Where can I find a set of data of the initial conditions of our solar system?

As title suggests I'm in need of a set of data of our solar system. Similar to this http://bima.astro.umd.edu/nemo/archive/#iau25, specifically dubinsky milky way-andromeda data. I'm creating a ...
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### Could an asteroid impact cause radioactive fallout?

Could a (regional or global) fallout of radioactive material be a "bonus" disaster effect of an asteroid impact? My reasoning for how such a scenario maybe could be possible: A) Some asteroids maybe ...
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### Why is Mars considered the outer edge of the “goldilocks zone”?

In both books and documentaries I often see the Goldilocks Zone as described between Venus and Mars with the Earth "just right." This seems sort of ill thought out to me, because it assumes that ...
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### Questions about time and space (from beginner)

To be honest my knowledge about astronomy and related physics is close to zero. However, since I studied math a bit, I would like to ask a couple maybe stupid questions, which I am curious about and I ...
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### Which type of telescope should I make?

I am not very much interested in observational physics but I just like to look at the night sky. It gives me a lot of inspiration. So, i was thinking about making a telescope for basic observations. I ...
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### What’s the object between the earth and the sun currently showing in Google maps?

If I select satellite imagery in Google maps and zoom out, the earth is shown in space. It shows light/dark regions correctly updated, but there’s an object between the earth and the sun. It looks too ...
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### Sattelite's orbit

What is the maximum distance for a satellite to orbit the earth? Does earth's gravity has the impact on satellite? I do know that earth's gravity will never be zero and it's gravity is inversely ...
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### How to get the longitude/latitude from solar zenith/azimuth?

How do I get the longitude/latitude from zenith/azimuth? Or how can I position my sun in a 3d application? code extracted from here ...