# All Questions

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### Basic DIY Telescope

I am looking for a design of a cheap and easy telescope to build with my 9yo daughter with the only basic requirement being that I'd love to be able to see detail on the moon. Looking around, there ...
7 views

### How can I make Stellarium match the magnitude of stars visible in London, UK?

Can someone recommend some Stellarium settings to mimic the amount of light pollution, and magnitude of stars that should be visible on a clear night in London, UK?
27 views

### Full Moon Position of Sun

I am trying to figure out the position of sun with respect to moon on a full moon day. Here's an image from certain wiki which I do not find convincing. 1 If the sun rays point as shown in the image ...
28 views

### Why do comets come from our local Oort cloud instead of from interstellar sources?

Comets form where stars form. And they are then ejected by the orbital changes of giant planets. But why are they ejected to form specifically a local Oort cloud instead of going interstellar and ...
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### Why is a star at its highest point when local sidereal time = RA (right ascension)?

I'm currently taking a course called Introduction to Astronomy at Coursera. It's not very formal so they didn't present a proof of the statement in the title. I understand why logically one could ...
10 views

### Is Nomad data heliocentric or geocentric?

I'm wondering if the data in star catalogues are heliocentric equatorial coordinates or geocentric equatorial coordinates. Also given the distance between stars compared to the distance between the ...
21 views

If there are indeed multiple universes, where do they exist? We "know" that outside our universe, consisted of spacetime, there is nothing - i.e. 0 dimensions, no space and no time. So "where" are ...
23 views

### How do we know an event is a gamma-ray burst?

How do we know an event is a gamma-ray burst (grb)? There are two kinds of grbs, long burst and shot burst, which are caused by supernova explosions explosion and the merger of two neutron stars, ...
15 views

### How do we get radio signals of the big bang?

From TV shows I have known that we still get some radio signals of the big bang and they are every where. My question is is the universe expanding so fast that even electromagnetic wave has failed to ...
8 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 ...
51 views

### Would Pluto keep an orbit without its moon?

I haven't studied space that much, but I know that Pluto has very little gravity, but just enough to keep a human on its surface. Would Pluto keep a regular orbit around the sun without some extra ...
39 views

### Photos from galaxy

So, I hear people say blah blah blah is 3 light years away, and here's a photo. So does that mean the photo that we see are actually at least 3 years ago since that's how long it takes that light to ...
18 views

### What is the boundary in the atmosphere seen in this video?

This video, which shows time-lapse views of Earth from the ISS, consistently shows some sort of hard boundary in the atmosphere, below which there seems to be significant reflection from sunlight ...
39 views

### How do we know that Voyager's data is correct?

I was wondering for some time how we know that the scientific data received by the Voyager spacecrafts are correct? Specifically, I'm wondering about the recent "tsunami-wave" (frequency of ionised ...
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### The role of gravity during planetesimal accretion

As far as I understand, during the formation of a planetary disc, grains of dust stick together due to collisions and chemical bonding. Considering the size of the grain - say, 1 mm - and the speed - ...
72 views

### How does Titan maintain the atmosphere

Titan which is smaller than mars has an atmosphere but mars is not able to maintain atmosphere. Even Luna doesn't have an atmosphere.
76 views

### Can A Black Hole Exist?

In 1939, Robert Oppenheimer and other concluded that a certain neutron stars could collapse to black holes and no known law of physics would intervene. As far as I can tell, there is no observational ...
33 views

### What is the Habitable zone all about?

I've a question on Habitable zone. Does Habitable zone represent the region where we humans or the living beings of earth can survive? Or is it a region where life can exist? If it is second I want ...
32 views

### Why dont we have a browsable spacetime augmented virtual solar system?

Wouldnt it be nice to be able to render any viewpoint from all the data transformed into a point cloud, an augmented virtual reality of moving objects in our solar system. I would just like to be ...
35 views

### Gravitational tidal force problem

if we have spherical mass held by its self-gravity, there will be a limit to distance - let's say it is r - that the center of this body may approach a much more massive body (lets we call M body). ...
29 views

### What to look for in a tripod for binoculars?

I have been looking at large astronomy binoculars in the 25x100 and 20x80 range. Clearly, these monsters cannot be held steady by hand, or even be held at all for any reasonable length of time using ...
60 views

### Limit of hotness!

We know that there is a limit to which an object can be cooled down that is absolute zero, and getting there is also not very easy we may have to wait infinite years to get to that point. But is there ...
42 views

### Is CMB Polarization simply the temperature gradient of the CMB?

Firstly, I have to admit that I don't fully comprehend the concept of "CMB Polarization". When I think of "Polarization", I normally think of the optical definition of polarization, as defined by the ...
228 views

### What is the exact mass of the Sun?

I am having trouble finding data on this. So far, I have found at least seven values: ...
367 views

### Are the stars in constellation located in a plane or they are in different distances

Are the stars in constellation located in a plane or they are in different distances from each other and when we observe them from the Earth we think they are all in a plane?
40 views

### Can Jupiter's bands be made out using a 15x70 pair of binoculars?

I have been getting mixed opinions on this. I have a 15x70 Pair of Binoculars. I have tried staring at Jupiter for several minutes with it, I was able to see the Galilean moons, in fact the last time ...
43 views

### Smallest body that can be observed from Earth?

What is the minimum size of an object that can be observed from Earth with our most powerful telescope? I understand that the answer depends on how far the object is from Earth. For the sake of ...
3k views

### Does the Earth have another moon?

I was just wondering what are the chances that there is a small object (say less than 1 km but more than few meters) that orbits the Earth but has remained undetected by us? Are we actually ...
55 views

### Look up current positions and velocities of solar system objects

I am working on an orbital dynamics code and, for fun, I would like to model the Sun-Earth-Moon system with my code. I can look up the masses of each object just fine, as well as average distances ...
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### Is there anywhere I can find some kind of database on all known stars and their properties (mass, surface temperature, radius, and luminosity)?

I have been looking for some kind of collection of all known stars and their individual respective mass/radius/temperature/and luminosity, can you link me to one if it exists? My goal is to write an ...
70 views

### What is the orbit of Earth around the Sun?

According to wikipedia and other sources, a planet and a star always move in a circular orbit around the common center of mass of the both bodies, in case of Earth and sun, this center of mass lies ...
73 views

### What determines the configuration of orbits in a binary system?

There are essentially two configurations of orbits a system with two bodies can have: A configuration where the paths do not cross: A configuation where the paths cross: Note: Size of the ...
49 views

### How would vehicles travel through the interstellar medium with its such low density?

I've heard from a number of different places that the density in the interstellar medium can have an average of 1 atom per centimeter cubed. Perhaps I have a wrong understanding of what 'nothing' is ...
67 views

### Stable polar solar orbit with the Earth continuously observable

Is there a stable polar solar orbit such that the Earth is always in view and not eclipsed by the Sun?
32 views

### Data for Sun's Orbit

The planets generally kindof orbit around the sun, but a more precise statement is that the planets and the sun all orbit around a common barycenter. Because the sun is so massive, this barycenter is ...
70 views

### Accretion disks - why are they disk-shaped, rather than spherical?

So, the theory (briefly) about accretion disks is that stuff falling into the black hole will most likely not fall straight into it but will miss it and go into orbit, perhaps for a long time, perhaps ...
39 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, ...
36 views

### How often and over what period is Earth’s rotation averaged to compute UT1?

I understand that UT1 (and for that matter UT0, UT2, etc.) are based on averages of actual earth rotation, and serve as a form of mean solar time. However it’s not clear to me when these averages are ...
20 views

### Orbital elements: Difference between longitude of perihelion and argument of perifocus

I am learning orbital elements and one thing isn't clear to me. When I look at the Horizon's ephemeris data for Mars, this gives me argument of perifocus equal to roughly 286.53 degrees on epoch ...
47 views

### Can an observer on Earth only see half of the sky?

Is this the following statement true? An observer on earth only may see half of sky from the northern or southern hemisphere, and even if the observer stands on the equator on top of a very high ...
59 views

### Solar System' formation, considering its and universe's age

It's been said that the sun has 4.6 billion years, and the complete solar system to have similar age. The star-class of the sun seems to be quite common. Stars of its class can have 8 or 9 billion ...
39 views

### What could be the results from the next test at CERN? [migrated]

How possible is it that CERN's Large Hadron Collider, on its second try, could disrupt the gravity of Earth?
29 views

### Is it possible to steer the sight of a Liquid Mirror Telescope using a plain mirror scheme? If yes, why hasn't it been done?

I have read about Liquid Mirror Telescopes in a number of places, and according to these sources, a major disadvantage of these telescopes is that they can only "see" straight up. In a nutshell, the ...
81 views

### Does planets repel

I know gravity is resultant of mass. Gravity is nothing but the attraction force on the body resulted due to its mass. I have a question may be silly but like in magnetism we have attraction and ...
3k views

### Is Jupiter made entirely out of gas?

I heard that Jupiter is made out of gas. But in school I learned that Jupiter has gravity which is 2.5 times that of Earth (Gravity that can tear apart a comet) and gravity is proportional to mass. ...
37 views

### Could a theoretical cube shaped planet have a moon? [migrated]

I'm inventing a constructed world for a personal exercise in writing, and I was wondering if a theoretical cube shaped planet could have a moon. Is that physically possible? I am going on the ...
31 views

### Manned journey to Mars [migrated]

Will we be able to take the amount of water that will be needed for this 18 month trip or will they have to recycle the water that they take with them ? I imagine that this will be quite a challenge ...
413 views

### 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 ?