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Questions tagged [space-geometry]

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3 votes
1 answer

visible solid angle of the moon

I'm reading an astronomy textbook for high schoolers, it contains an exercise to calculate the visible angle ratio of the moon in the sky (the textbook is not in english so my terminology is probably ...
Orion.55290's user avatar
2 votes
0 answers

What happens at the edge of a finite and "bounded" universe?

So far, we know only about two types of universes: Infinite and finite universes (Unbounded edition). In an infinite universe, there is no edge. Because well, an infinite space doesn't have an edge. ...
Alastor's user avatar
  • 2,668
2 votes
2 answers

κ₀ for Mercury—Formula

I refer here to Ptolemy’s epicycle-and-deferent model of the Solar System, specifically that of Mercury (see drawing). In this model, Mercury (not shown) revolves on an epicycle of center C, which ...
Pierre Paquette's user avatar
2 votes
1 answer

By analytical geometry, how to calculate the fraction of the visible area of the Sun at a point during an eclipse?

Assume a perfectly spherical Sun and Moon, and ignore atmospheric effects for simplicity. I'm an observer in the origin of my coordinate system, and I know the positions of the centers of the Sun and ...
arda güler's user avatar
1 vote
0 answers

Spacetimes where symmetries vary from place to place?

Are there spacetimes or metrics where symmetries (like Poincaré, Lorentz, diffeomorphism, translational... invariances) are only local and the symmetries of one local neighbourhood are not, a priori, ...
vengaq's user avatar
  • 1,017
2 votes
1 answer

Are there non-smooth metrics for spacetime (that don't involve singularities)?

I found this statement in a discussion about the application of local Lorentz symmetry in spacetime metrics: Lorentz invariance holds locally in GR, but you're right that it no longer applies ...
vengaq's user avatar
  • 1,017
0 votes
1 answer

Can the curvature of a closed universe be measured?

Suppose we were in a closed universe likened with a spherical surface such as that of the Earth's surface. Assume also that the limits, represented by the limits of the observable universe, ...
Mikael Jensen's user avatar
6 votes
1 answer

Can we consider the Universe to be some kind of 3-sphere?

This is probably a naive question. I'm learning a bit of cosmology and I've recently covered the so called angular size-redshift relation, which states that in an expanding Universe the angular size ...
Swike's user avatar
  • 3,926
4 votes
3 answers

How to calculate the nodal precession range of the Moon with respect to the celestial equator?

In the span of 18.6 years there is nodal precession of the Moon with respect to the ecliptic of 360 deg. But if we consider this precession with respect to the equator, we will find (unless I'm hugely ...
d_e's user avatar
  • 1,667
2 votes
1 answer

What is the thickness of black holes event horizon?

I would premit that I am just an enthusiast, so don't expect a good background or a deep mathematical knowledge about the topic. I just read an article about how light is reflected by a black hole (...
Skary's user avatar
  • 173
3 votes
1 answer

What do falsifiability and verifiability actually mean as a precondition of a scientific hypothesis?

What do falsifiability and verifiability actually mean as a precondition of a scientific hypothesis? I have been hearing from science guys that unlike philosophical hypothesis or theory, to be a ...
Sazzad Hissain Khan's user avatar
1 vote
0 answers

Determining observer's position based on azimuth and elevation of observed object

It is possible to generate Ephemeris through the web-interface of JPL's Horizon system based on observer's location. Unfortunately I don't know the formula that is used to do that with a high ...
Alieniasty's user avatar
5 votes
2 answers

Data to "check" Kepler’s first law

I want to "check" Kepler’s first law by using real data of Mars. From the equation of the ellipse, I derived $$\frac{1}{r}=\frac{a}{b^2}+\frac{a}{b^2}\cdot\epsilon\cdot\cos(\varphi),$$ where ...
Joe_base's user avatar
2 votes
1 answer

Why both sunrise and sunset use the position of the sun's upper limb?

It is my understanding, that astronomical moments of both rise and set use the relative position of background object's upper limb to the foreground object's horizon. When were these definitions ...
user avatar
7 votes
0 answers

Get the expression of probed volume between 2 redshifts

1) I can't manage to find/justify the relation (1) below, from the common relation (2) of a volume. 2) It seems the variable r is actually the comoving distance and not comoving coordinates (with ...
user avatar
4 votes
1 answer

Is it possible to overcome the problem of blind spot(s) of current gravitational wave detectors?

If gravitational waves (GWs) pass through specific points (which are known as blind spots), current GW detectors aren't able to detect the passing waves. In the future, will we be able to completely ...
learner's user avatar
  • 341
5 votes
1 answer

What decides the shape of a galaxy?

As I know, most galaxies are spiral, some elliptical, and a rare type is ring-shaped. What causes a galaxy to become a specific shape (i.e. ring vs spiral)?
Samid's user avatar
  • 151
3 votes
2 answers

How is the size of a distant planet determined?

How is an object's size determined from other solar systems than our own? How are new large bodies being found in our solar system currently?
Muze's user avatar
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1 vote
1 answer

What prevents consequent eclipses? [duplicate]

I know there are a number of parameters that determine the occurrence of a solar or lunar eclipse. The number should be 18; 6 degrees of freedom for 3 rigid bodies. But can't figure out why eclipses ...
jeff's user avatar
  • 233
10 votes
2 answers

How did we first determine the Earth's departure from sphericity?

I'm quite interested to know the history of the study of the Earth's departure from spherical symmetry. What were the first methods used to model the non-spherical geometry of the Earth? For example, ...
Rumplestillskin's user avatar
-1 votes
1 answer

Why is the volume of Saturn is 764 times bigger than Earth, but its surface area only 83 times bigger? [closed]

If Saturn is 83x bigger that Earth by surface area why isn't the volume also 83x bigger than earth by volume? Is there a geometric or astronomical reason?
user16821's user avatar
30 votes
6 answers

Is the universe considered to be flat?

I've read various articles and books (like this one) stating that we are not certain about the geometry of the universe, but there were experiments on-going or planned that would help us find out. ...
ivanmp's user avatar
  • 403
3 votes
1 answer

How to project galaxy data in x y z coordinates?

For a data visualization project, I want to extract galaxy data (in x y z coordinates) from galaxy catalogue of within 150 mpc and project each of those galaxies as dots and visualize them in a 2D ...
Manny S's user avatar
  • 39
5 votes
1 answer

Does the sky get darker faster during the winter?

When one lives away from the equator, say at around 37° latitude, does the sky get darker faster after the sun sets in the winter as compared to the summer? Why is this the case? I believe that if ...
WilliamKF's user avatar
  • 287
3 votes
1 answer

How certain are we about the universe's flatness?

The universe is thought to be flat: $\Omega = 1 \pm 1\%$. As I understand it we can determine this by measuring triangles against the CMB. Yet during inflation dark energy made the universe grew ...
stevenvh's user avatar
  • 803