# All Questions

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### Will Hubble's law always be accurate?

We have Hubble's law: v=Hd where H is the Hubble parameter, which is decreasing in value, but it will be constant in the distant future. So, assumming the Standard Model of Cosmology holds true, ...
81 views

### Is there a mechanism that makes small moons more rounded than comets?

67P/Churyumov–Gerasimenko has a highly irregular dumbbell shape. But the sample of comet shapes observed is very small, so I wonder if irregular shape is the norm for comets and for small moons. Many ...
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### How did WASP-18b exoplanet form?

I am new to this community and not quite sure if this is an appropriate question to be asked here. Anyways its just my curiosity. As far as I could know about WASP-18b is that, it orbits very close to ...
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### radial velocity fitting of a binary

I have two series of velocities (HJD, $v_{1}$ and $v_{2}$ ), how to fit in detail? There is any formula on the web? $sine$ curve is easy, but I need to consider an eccentric orbit. Suppose we can ...
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### Halpha velocity fields of spirals falling into a cluster

What kind of impact would you expect ram pressure stripping / tidal interactions / harassment / interactions with the cluster potential (etc!) to have on the h-alpha velocity fields of infalling ...
135 views

### Day Length on Double Planets

Assume two similarly sized bodies tide-locked to one another orbiting a barycenter between the two. That barycenter orbits a star. Since the two are tide-locked, their sidereal rotational period and ...
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### How can we tell how many exoplanets a star has?

Part of this answer (discussing the moving center of mass of our solar system) explains that this movement is one way we know a star has planets: Bonus: We use this phenomenon to find planets ...
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### Is our universe included inside a black hole?

This question repetitively comes to my mind but I've never found any good scientist article to argue about it, only esoteric or speculative web articles without much valuable background. So let's ...
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### Question about extreme space distortion and creation of a new dimension

In all the illustrations regarding space distortion, I find an extra dimension that depicts space distortion. Is there any mathematical equation that proves the creation of an extra dimension ? ...
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### Why is dark energy preferred to the cosmological constant?

Dark energy and the cosmological constant are often identified, but Peebles and Ratra explain that "Einstein did not consider the cosmological constant to be part of the stress-energy term... a ...
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### How close are we to be able to detect and measure gravitational lensing inside the milky way?

Gravitational lensing takes advantage of statistically uniform distributions of background objects in order to infer a credible map of dark matter concentrations that isn't too noisy. If there are too ...
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### What more could be learned from a rare astronomical event if we knew precisely when it would occur?

This is actually related to a question I recently asked on Worldbuilding, but seemed more appropriately asked here. To keep this from being too broad in scope, let's assume that someone figured out ...
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### 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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### How did Meeus calculate equinox and solstice dates?

In Astronomical Algorithms (2nd ed, ch. 27, 2009 corrected printing) Jean Meeus gives expressions to calculate the date and time (dynamical time, equivalent to Terrestrial Time) of equinoxes and ...
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### What's in the center of a Galaxy?

Ok, so it's supposed that there is a black hole in the center of any galaxy, that makes my head explode because: There is light in the center of the galaxy, but it is supposed that black holes, also ...
139 views

### Is Mercury's core liquid?

A very basic question, but one to which I keep finding different answers: does Mercury have a liquid core, or is it all solid? Whatever the reason, what are the causes of it being so?
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### Is there a difference between the terms 'elliptical' and 'elongated' for galaxies?

While studying the Solar System, I found that some galaxies are either elliptical or elongated. What's the difference?
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### Interstellar movie: What is the “portal” to the other galaxy?

I recently watched Interstellar with some friends and we didn't come to the same conclusion. In my opinion, the portal they use to go to the other galaxy (to visit the three planets) is not a black ...
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### Why don't Australia/Russia have large optical telescopes?

Australia and Russia have large land areas. However, I am only aware of one 3.9m telescope in Australia. As far as I know, there are lots of mountains in Australia and Russia. So why are there not ...
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### Eternally collapsing objects?

As has been pointed out by some scientists, that black holes aren't stable bodies but are eternally collapsing objects. How does one come to such a conclusion? Is hawking radiation related to this in ...
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### Is mass+energy conserved when a new universe forms inside a black hole?

My understanding is that there are credible theories out there in which the formation of a singularity in a black hole also represents the beginning of a new universe via a big bang. We can't see the ...
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### What kind of things I could “see” with an amateur radio telescope?

There are apparently not many reasonably priced radio telescopes available for the amateur users. I only could find this one, which costs ~10 k€. Reading the page, I don't get a good overview what ...
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### Collapse of a star below the mass of Chandrashekhar Limit

How is Chandrashekhar Limit calculated? What happens to stars below the mass of the Chandrashekhar limit after they collapse?
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### Focusing light through fiber optic cable to extend telescope viewer

I want to build a system to view my telescope without being uncomfortable. Currently I have to stand up and bend over to view the eye piece. I want to build a system that allows me to 'pipe' the ...
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### How Much Overlap Will the Andromeda Galaxy and the Milky Way Have When They Collide?

Measurements of Andromeda's blue shift let us conclude that the distance between the Andromeda galaxy and the Milky Way is decreasing and in a few billion years they will "collide". The blue shift ...
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### How is the cost of JWST distributed on different parts of development and operations?

The James Webb Space Telescope costs nearly 9 billion dollar. What parts of this project cost how much? I suppose that almost every component has to be developed and is not available to buy off the ...
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### Am I using my Celestron 8 Schmidt-Cassegrain telescope correctly?

I became interested in astronomy a few years ago and started with a Celestron AstroMaster 70AZ refractor telescope. That seemed nice, and I wanted to upgrade to a go-to telescope that was also more ...
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### How well do planetary orbits fit with Johannes Kepler's in- & circumscribed Platonic solids?

In Mysterium Cosmographicum (1596) Johannes Kepler proposed that the relative distances between the orbits of the six ancient planets (six because heliocentrism had recently added Earth as one of the ...
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### Capturing Ceres

Would it be possible to slightly change the trajectory of Ceres to make it end up orbiting the Earth without messing up the Solar System? How much energy would be required and how long would the ...
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### Can there be an object with planetary discriminant between Ceres and Neptune?

The planetary discriminant is a measure of how dominant a body is within its region of the solar system. For (true) planets, it is $>10000$ and for dwarf planets it is $<1$. (See this answer to ...
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### Do the planetary ring lasts? [duplicate]

Almost all gas giants in our solar system are observed to have a planetary ring comprises of ice, dust and rocks. My question is do these rings obediently sticks around their foster parent until our ...
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### What are the analysis steps in taking raw data from Kepler to a planetary system determination

I wish to get a concise list of the analysis steps required to take raw light data from a Kepler data set of a star through the steps needed to get to an analytical determination of the existence of a ...
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### How much time comet is within the Earth's orbit? [closed]

Comet on the parabola orbit flies by Sun. I would like to know what is comet's full energy? What is its distance from Sun at perihelion?
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### How to calculate full (mechanical) energy on the hyperbolic orbit?

For example, for a comet that travels on the hyperbolic orbit around the sun.
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### Asteroids in langrangian Points 4 & 5

There are Asteroids "trapped" in Jupiters Langrange points 4 and 5 called trojans and greeks. Are there any asteroids in the earths L4 and L5? Have we seen asteroids in Lagrange points of the earth ...
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### Michigan's Pole Star

Unfortunately, I'm not any good at figuring these things out myself so hope for help here. If the (true) north pole were over the Keweenaw Peninsula of Northern Michigan, what would the North Star be; ...
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### How to deal with shifting CCD bias (zero exposure) levels?

The median values of the bias frames coming from our teaching telescope shift up or down with each capture. For example: ...
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### What is the reason for the dispute over the variation of core mass with heavy metal abundance?

In Metal-Poor Stars IV: The Evolution of Red Giants, Rood writes The differences in the results of these papers are large enough to introduce appreciable uncertainties into the study of the ...
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### coordinates in ICRF

The International Celestial Reference Frame (ICRF) is defined based on distant quasars and the origin is the barycentre of the Solar system. So, how can we measure the coordinates (\alpha, \delta) of ...
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### why are solar telescopes built on lakes? the site differnece between a solar and an optical telescope

According to the wikipedia page big bear, water can cool the observatory. Big bear is in the southern California. It is better to build it on a cold high mountain with stable and clear atmosphere? ...
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### How is the age of a star on the Henyey track calculated?

I was reading Stellar Evolution in Early Phases of Gravitational Contraction, by Chushiro Henyey, where he writes, If $L \propto R^{-\alpha}$ along the path, the age of a star from the time when ...
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### Sunsets: Mars/Earth

I understand why our sky is blue and turns red when the sun sets or rises. I know why the sky on mars is red, but why does it turn blue during sunsets and rises? Shouldn't this actually not work due ...
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### For how many bodies can there be a stable orbit with no very heavy central body?

The question is a bit vague, but let me explain: Take for example 2 bodies of the same mass. They can orbit around their centre of mass/gravity. Is something like this possible with multiple ...
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### Types of Exoplanets

We discover vastly more exoplanets, that are gas giants that orbit their parent star very closely, than small terrestrial planets that are more distant to their sun. Could this be due to the methods ...
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### Probability of finding life-supporting exoplanets

We've found over a thousand exoplanets by now, but how many of them could support life? What percentage of newly found planets are potentially life-harbouring? Or haven't we found any exoplanets that ...
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### Why aren't secondary mirrors offset to get rid of diffraction spikes due to the support vanes?

Some kind of ellipsoidal shape mirror could reflect to a secondary mirror which is not in the way of the infalling light. Two advantages are immediately obvious. The primary mirror would not be partly ...
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### Can the Milky Way be seen with the naked eye? Does this apply to any galaxy? If yes, then how and when?

I have seen different pictures in a different community to showcasing the Milky Way. I can never tell whether it's edited or it's the real picture. Actually, I can never see any galaxy as such by with ...
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### Milky Way stellar number density : is the stated equation in this paper incorrect?

The paper is : http://www.astro.washington.edu/users/ivezic/Publications/tomographyI.pdf The equation is equation #23 in the paper. It's a model for the density of stars in the Milky Way's disk. It ...