# All Questions

194 views

### 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 ...
85 views

### Are galaxies moving away with constant acceleration?

Suppose that we could measure the current acceleration with respect to us of a distant galaxy chosen at random in our observable universe (Ignore the peculiar motion of the galaxy). Is the ...
113 views

### Is there a general term for epicycles, deferents, and eccentrics in Ptolemaic astronomy?

According to Ptolemy's (c. 150 CE) account of the motions of planets, planets moved in circular paths ("epicycles") around center points that in turn moved around the center of the earth along a path ...
162 views

### How would the solar system look in a Geocentric model?

If I fix the Earth as the center of the solar system, what would this look like? Are there any good images? How complex is this system?
249 views

### What is a Galactic Eclipse?

It is said that when our solar system passes through the dark rift of galaxy (what is it exactly?), a phenomenon named 'Galactic Eclipse' happens, when our solar system witnesses 3 days of darkness. ...
67 views

### Did Big Bang sound as loud as we think?

As we all know, There is no sound in space, because sound waves don't travel in a vacuum. But even if Big Bang did sound, what was the main source of it's cause?
81 views

### How did the moon's orbit become eccentric?

The Moon's orbit is more eccentric, 0.0549, than most planets. I can understand that planets get eccentric by disturbing each other like under the late heavy bombardment. And likewise for multiple ...
54 views

### Has SETI data been used for astrophysics? How, or why not?

SETI collects alot of data from space, mostly radio. I wonder if this data has any astrophysics value other than SETI?
41 views

### An anti-black-hole-engine

I'm just a fan of astronomy. Let's imagine humanity has limitless possibilities. How is it possible to create an anti-black-hole-engine? I mean everything inside reach of the engine can move inside ...
281 views

### What is the difference between gas and dust in astronomy?

Is there a strict difference between gas and dust? In Earthly environment most things become gaseous if heated enough. The temperature of interstellar medium seems to range mostly between 10 and 10 ...
107 views

### What is a possible software for simulating binary star systems?

I would like to define both initial velocities and masses of components so that orbits may be either elliptical of hyperbolic. Is there any software to make such simulation? Unfortunately, Binary ...
48 views

### Looking for planetary position calculation

In Hindu astrology, for creating horoscopes (birth charts), I am looking for calculations of planetary positions. So, how could I calculate planetary positions according to given date, time and place? ...
54 views

### What's the significance of finding neon on lunar atmospehere? new explanation of moon light?

Now that NASA's LADEE spacecraft has confirmed the presence of Neon in the moon's atmosphere could the official explanation of the moon's light end up being change from reflecting the sun's light to ...
65 views

### How does 'centre of mass' concept work?

We know that two celestial bodies rotate around a center of mass. How does this concept work in case of solar systems where there are several planets versus one/two stars? (Even if the center of mass ...
14 views

### Standard conditions for a heliacal rising

I imagine there are several possible conditions for determining the time of a helical rising of a star, the elevation of the star at sunrise, the latitude of the observer, and the azimuth of the star. ...
101 views

### How Are Radioactive Decay Rates Influenced by Neutrinos - On Earth and Other Dense Planets

I read a science report recently that mentioned an accidental discovery where radioactive decay rates shifted slightly slower in advance ( about a day and a half) of solar storms or in sync with sun's ...
82 views

### What's the difference between grism and grating?

In spectroscopic observations, sometimes you meet grism, sometimes grating. Both of them could cause light dispersion, but what is the difference?
32 views

### What is the mass limit in a stellar accretion disc?

I became curious about the maximum mass in a star's accretion disc while watching an episode of Star Trek involving a Dyson Sphere. I wondered if some maximum amount of stellar material would limit ...
72 views

### Method to determine the amount of reflected starlight necessary for an exoplanet to be visible from a given distance/angle?

What is the method to determine the amount of reflected starlight necessary for an exoplanet to be visible from a given distance/angle? (Not from occlusion but actually visible on its own.) Further, ...
129 views

### Why do objects all orbit in the same direction?

In a solar system or a planet that has many moons, why do their orbiting objects all orbit in the same direction? Is it possible for two orbiting masses to orbit in the opposite direction of each ...
51 views

### What's the distribution curve for meteor sightings?

I know that meteor showers have a "peak" observation time. What does the distribution in time look like? Is one side of the peak steeper/shallower or longer/shorter than the other side, and if so, ...
48 views

### How do you determine which star, between two, is more luminous?

For example, if star 1 is 4x bigger than star 2 but both are the exact same temperature how do you determine which is more luminous?
110 views

### Isn't the date of the Big Bang a bit bogus?

If I understand correctly, the date of the Big Bang is an extrapolation of acceleration of the universe's expansion through time based on the erroneous assumption that the universe is approximately 13 ...
130 views

### Precessing of the Earth

It's been known that the Earth's axial tilt varies from 22.5 to 24.5. Does this result in a wobbling while the value of the tilt varies about these two limits? If so, how does it affect the mechanics ...
23 views

### attractors of Mercury's spin-orbit relation

Mercury rotates at such a rate that the Sun appears to stand nearly still at perihelion, when the tide is strongest. Is there a mechanism that tends to adjust the orbital eccentricity to improve the ...
138 views

### Are there heavenly bodies between galaxies?

I do understand that galaxies were formed in the famous Big Bang. However, I also understand that if such an explosion occurs in empty space it will never form distinct galaxies, it should more or ...
116 views

### How can we be 13.2 billion light years from another galaxy?

How did we get 13.2 billion light years from the faraway galaxies being discovered with Hubble? If we all started near each other at the Big Bang, and we all travelled slower than the speed of light, ...
78 views

### How do I get from Star Atlas to real life?

This question is about finding the elevation and bearing of a given star at a particular time at Latitude 52N. I look up the RA and Declination of my star. How do I calculate its RA and elevation at ...
55 views

### Calculate time when star is above altitude 30°

To find the best observation time for an object, I'd like to calculate the time when it is 30° or more above the horizon. Local Sideral Time would be sufficient. To include that in my program, I need ...
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### Why is the E-mode polarization spectrum out of phase with the Temperature spectrum?

The E-mode polarization power spectrum of the Cosmic Microwave Background displays the same acoustic peaks that can be seen in the (more famed) temperature power spectrum. However, they are out of ...
96 views

### Does “Dark Matter” really exist?

Does dark matter really exist or is just a made-up theory in order to cover up the loopholes in the Big Bang theory, and also to explain why universe is expanding at an accelerated rate?
55 views

### Problem with Dobsonian reflector telescope

I'm not sure whether I should ask this question here but I'll give it a shot. I have a XT8 Dobsonian Reflector telescope and it works fine. But recently when I use the focuser to focus the image when ...
434 views

### Why did the big bang not just produce a big black hole?

Questions I've often wondered about: 1) If all the matter and energy were concentrated at a single point at the big bang, why wasn't that a black hole, or why didn't it form one? 2) If the reason #1 ...
6k views

### Did atoms in human body indeed come from stars?

I think I am not alone who saw videos about that we (humans) are made of same atoms which someday were in stars. In other words, some atoms in our bodies are from stars which exploded billions of ...
50 views

### If earth were the size of a marble would it be smoother than a marble? [closed]

As the title states, If earth were the size of a marble would it be smoother than a marble?
953 views

### How long until we cannot see any stars from other galaxies?

Since all the galaxies are moving further away from each other at a faster and faster rate, eventually we won't be able to see stars from other galaxies. How long until we can't see stars from other ...
69 views

### If oxygen were pumped into space where would it go?

If an astronaut went into space with a sealed container of oxygen and opened it up in space and let all the oxygen go, what would happen to it? would it all just dissipate into some other particle or ...
144 views

### How has the Earth's orbit changed over hundreds of millions or billion of years?

First, I know that modeling orbital mechanics of 8 planets is hard, but there are some theories out there, for example, Jupiter is thought to have moved in towards the sun then started moving away. ...
174 views

### What is the bluest narrow band filter mounted on ground based telescopes?

If we want to check a QSO's lyman alpha narrow band image, could a ground based telescope do that? I mean under the circumstance that its lyman alpha shifts to 3300A.
139 views

### Are those noise or stars?

So there is this huge picture by Hubble. Better yet, with the zoom tool And if you zoom to the maximum level, you can see a seemingly uniformly distributed dots of orange and blue. Are those ...
147 views

### What is the difference between LMC and SMC?

Apart from the obvious difference as suggested by their names that the Large Magellanic Cloud is 'larger' than the Small Magellanic Cloud, what are the other differences between them? Do give all the ...
81 views

### Southern hemisphere is short of radio telescopes? [closed]

In northern hemisphere, we have GBT, Arecibo, Parkes, Jodrell and VLA, while in southern hemisphere, only Australia has big radio telescopes. ALMA is in Chile, but it is in submm. It is not ...
40 views

### Is there some upper limit in the moon size distribution?

The planets range hugely in sizes, Jupiter is more than 300 times as massive as Earth. But the sizes of the large moons seem to be uncorrelated with the sizes of the planets they orbit. Why doesn't ...
68 views

### The universe is dying vs the universe is ever expanding

How does the idea that the universe is dying (trumpeted as some big new revelation the past few days on several new sites I keep seeing pop up on google news) square with the idea that the universe is ...
23 views

### How could eclipse happen on the same day in a different calendar? (45 AD)

According to the eclipse calculator I use (Alcyone), a partial eclipse 0.314 magnitude occurred August 1, 45 A.D. in Rome starting at 8:35am local time. This would seem to correspond to an eclipse ...
103 views

### Do all planets have a van Allen radiation belt?

Earth has the van Allen radiation belts. Which other planets have one? Can it be determined if distant planets in other solar systems have one?
43 views

### Configuration required to tidally heat Earth-like rogue planet

Could it be possible for Earth-like rogue planet to maintain large bodies of liquid water on the surface without a sun by relying mostly on tidal forces of a moon (or multiple moons). How big/far/fast ...
139 views

### Ramifications of black hole stellar system

Recently, I got around to seeing the movie Interstellar. In it, the characters of the movie visit a stellar system that appears to be built around a black hole instead of a star. On top of this, their ...