# All Questions

7,487 questions
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### Dynamical modelling of galaxies with counter-rotating components using the Schwarzschild method

I am currently trying to understand dynamical modelling using Schwarzschild's method. I have been doing some reading the past days, but I suspect that I am getting something really wrong. According to ...
381 views

### Why things float in space, though there is always gravity of our star is present

In the solar system, things float around. We are so certain that the gravity of our sun exists. Still, why does that gravity not influence satellites and other objects there. Our solar system is also ...
41 views

### How to find the source of the light

There are millions of galaxies out there in the entire universe. When a telescope is set to a direction to to identify the stellar objects, it can capture all lights from all the objects. How do we ...
52 views

### If the space is expanding near the speed of light or the speed of light, why Andromeda is approaching or coming near to our galaxy (Milky way)? [duplicate]

Space with distance of 1megaparsec is expanding with rate of 70km/s, and if space with a distance of 4296 megaparsec is expanding at rate of 300,720km/s, then why Andromeda is coming to us? Even there ...
56 views

### Black holes in galactic rotation [on hold]

I'm wondering whether the total mass of a galaxy's hypothetical black holes, that may have each been formed within the gravitational horizons of larger black holes (that are indirectly apparent, ...
21 views

### If space is negative energy and matter is positive energy then does that mean the universe is finite?

I was reading a book by Stephen Hawking, it was written that universe is made up of 2 ingredients,i.e., space and energy and space was the negative energy, so they add up to 0. But since space is ...
71 views

### The Expansion Of The Universe [on hold]

I am informed that a volume of nothingness can expand many times over for no good reason,becoming filled as it does so by colossal numbers of virtual particles which appear ultra-briefly out of ...
1k views

### How “fast” do astronomical events occur?

I've seen quite a few news about astronomy but I'm not deep into knowing how it works or how people observe it. It got me thinking: if I want to watch a supernova for example, how long will I have to ...
82 views

### Stars readjusting themselves in the sky [duplicate]

I had a meeting in the evening and thought of grabbing a snack before that. I stepped out of the office along with a colleague. He was on his phone and I was simply staring at the sky wishing it would ...
57 views

### Why do heavy objects bend space-time downwards? [on hold]

Einstein's general theory of relativity is famously demonstrated using stretched sheet and marbles. We all know the demonstration. But its GRAVITY itself which makes the stretching of the sheet ...
236 views

### Is it possible to know if you are travelling close to the speed of light if you have nothing to compare your speed with?

This is a question that has been bugging me for some time. Let's see if I am able to make me understood! Imagine you are travelling in a spaceship at 99.9999999999% the speed of light and you are ...
805 views

### How do CMB photons 'gain energy when they pass through normal regions of space with matter' and 'lose energy when they pass through voids'?

The Space.com article Huge Hole Found in the Universe says: The gargantuan hole was found by examining observations made using the Very Large Array (VLA) radio telescope, funded by the National ...
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### How do we know the radius of the universe is 47 billion light years?

Hubble deep field image at maximum resolution shows a few of the furthest galaxies very small & faint, only just visible, but suggests that there is more to see beyond if only the resolution were ...
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### Black hole properties [duplicate]

Black holes are things with immense gravity.Inside black holes gravity is much stronger than any other fundamental forces.But is strong enough to overcome Pauli repulsion?
150 views

### Struggling to understand the phases of the moon

Source Typically this diagram is how the phases of the moon are explained but the issue is this, namely, the phases seen on the right half are not possible. All the phases should appear on the left ...
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### Does the density in the core of a “higher mass” star stay generally constant while it evolves on the MS?

We know the CNO cycle produces the majority of energy production in a "higher mass star" of approx. over 2 solar masses and the core is convective due to the large temperature gradient. My professor ...
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### Hypothetical: Is the interstellar wormhole too close to the black hole? [on hold]

Most reasonings about hypothetical wormholes say, that you need an extreme amount of energy to keep them open. Given that, isn’t the worm hole too close to the black hole gargantua? The gravity ...
103 views

### What Is The Maximum Distance Our Finest Instruments Could See When They're Perfected?

Radius of the observable universe is 47.5 billion light years,which means we are seeing things which are about 48 billion light years away. At a rough estimate,at what distance would our finest ...
10k views

### Why can't we feel the Earth's revolution?

I googled it and checked a few Q&A and there's only things about "Earth's rotation". But why can't we feel the revolution? They say we can't feel the rotation because the Earth spins at a ...
40 views

### Exposure time for spectroscopy compared to photometry

For a report I'm writing, I'm interested in comparing the exposure time required for spectroscopy versus photometry for a given magnitude. I found the figures on pages 7 and 8 of this lecture ...
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### Causes of emission of accretion disk

As far as I can see, there are two main sources for the emission of energy from an accretion disk: release of gravitational potential energy of the infalling matter; friction from differential ...
1k views

### Why didn't all the iron and heavier elements find their way to the center of the accretion disc in the early solar system?

I guess that's pretty much it. I just heard that that a meteor fragment was found to be solid iron and it just seems inexplicable that it was floating around.
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### How can the oblateness of Earth impart torque to change the longitude of ascending node of a satellite?

I've read that you can change the longitude of ascending node of a satellite (i.e. changing the orbital plane without changing the inclination) to change its orbital plane by using the torque imparted ...
66 views

### why do we keep using the term tidal locked? [closed]

So many astronomical terms are being used incorrectly. Tidal locked is not when a celestial body rotates at the same rate as the body it is tied to, only showing one side. If a celestial body has no ...
139 views

### What does it mean for space to expand?

In this YT video Michelle Thaller says The Big Bang wasn’t an explosion but an expansion and as such there's no empty center where the explosion would've been. To explain expansion she uses the ...
834 views

### Recording Spectral Lines at Home

I was wondering if it would be possible to record the emission/absorption spectra of stars without expensive spectroscopy equipment. Would it be possible to somehow utilize diffraction grating? I own ...
339 views

### Quasar Redshifts

How can the gravitational redshift of a very distant quasar be distinguished from its cosmological redshift? Quasars are very massive objects,thought to be supermassive black holes,so therefore must ...
54 views

### Draw the celestial sphere for latitude, showing the star Sirius, Estimate the approximate date when Sirius rises with the Sun

I'm having trouble understanding how to solve a certain problem. The problem is from the book Astronomy: Principles and Practice by Roy and Clarke. It is actually a solved example, but I am unable to ...
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### evaluate solar eclipse Besselian elements? [closed]

I found this NASA website which says that to predict eclipse, we should solve the Besselian elements ..what does this mean, how can I solve for Besselian elements? Is there a numerical method? I need ...
75 views

### In what form was dark energy stored 6 billion years ago?

Bearing in mind the provisions of the 1st Law of Thermodynamics, which decrees that energy can neither be created nor destroyed, all the energy in the Universe must have been there at the time of the ...
115 views

### Using emission lines to determine redshift of a quasar

I am attempting this past paper question and am not sure how to tackle this, this is not homework! :) The spectrum of a distant quasar shows two broad emission lines with observed wavelengths of ...
36 views

### Plotting Galactic Longitude from 180 to -180

I made a scatter plot in Python that looks like this: However, I want galactic longitude, l, to be plotted from 180 to -180 like these graphs from Iorio and Belokurov (2019): Here is the ...
62 views

### Converting an RGB image to fits (astropy)

I am trying to save a NumPy RGB array (a 3d array with dimension 512x512x3), to a .fits file using astropy.io. Saving this array to a .png file works fine, but when ...
69 views

### Custom telescope

I am currently trying to make a Keplerian telescope from "scratch" with plano-convex lenses bought online. I have found my objective and eyepiece lenses. I'm just not sure if they will suffice to ...
52 views

### Discrepancy Between Results of Cosmological Observations & the Assertions of Quantum Mechanics [closed]

Quantum mechanics requires a vacuum energy 40 orders of magnitude higher than that indicated by cosmological observations. Which side is most likely to be right,& when the truth is finally ...
159 views

### What's the actual speed of electromagnetic radiation in space?

The speed of EM radiation is very slightly less than $c$, because space is not quite a vacuum. Say EM travels at $(1-\varepsilon)c$. For example, this results in a slight delay between receiving a ...
147 views

### If fusion only happens near the center of the sun, what's with all the “fire” on the surface?

I understand that it isn't "fire" in the combustion of oxygen sense, but I can't find an answer online about what we're witnessing happening at the visible surface of the sun if all actual fusion ...
58 views

### Sorting out Julian Day, Julian Date, Julian Day number, Julian Day Calendar, and Julian Day Table

In this answer I mention day number which is 1 on the first day of each calendar year (January 1) and increments to 365 or 366 on December 31 of that year. There was an edit proposed, which included ...
26 views

### Full picture of our galaxy from the outside [duplicate]

How far a spaceship should travel to take a full picture of our own galaxy from the outside?
25 views

### Are horizontal branch stars fully convective?

I know that RR Lyrae stars are convective (this is suspected to be part of the cause of the Blazhko effect), but I would like to know more generally: Are RR Lyrae fully convective? Are all HB stars ...
32 views

### Plot SuperWasp Lightcurves

I am trying to plot superwasp lightcurves in python from the fits files, using TMID and FLUX2, getting this: There is a way to transform the information so I can plot the lightcurves with the kepler ...
31 views

### Are occultation observations used/useful for orbit determination?

The IAU Minor Planet Center lists $(486958)\space 2014 \space MU_{69}$ "Ultima Thule" as having an uncertainty parameter of 2, based on the observation arc of 851 days, from its discovery in 2014, to ...
133 views

### What would you find within a void?

I'm aware that voids are relatively empty regions of the universe, but just how empty can they be? Wikipedia states that voids have 'few or no' galaxies, but I can't find much else. To make my ...
63 views

### Are any bow shocks seen in the visible spectrum?

Are any of the images of bow shocks created from visible light, or are they all from infrared light? While I'm including two of the better known images, my question is about any known bow shock. LL ...
35 views

### How do they know the X-ray and radio intensity really come from a magnetic field bridge between these two clusters of galaxies?

Gizmodo's Astronomers Spot Mysterious, 10-Million-Light-Year-Long Magnetic Field Connecting Two Galaxy Clusters shows the image below, and Space.com's A Weird 'Radio Bridge' 10 Million-Light Years ...
55 views

### How can we calculate velocity of an object given the distance from an object in parsecs?

If you had the distance from a celestial object, in parsecs, how would you calculate the velocity of the said object? Edit: I'm sorry I don't have more context, the specific questions is: "A galaxy ...
67 views

### Why is true and average anomaly of planet important?

Why is a true and average anomaly of the planet important? What useful information do they give us?
28 views

### Comet mass loss

As the comet orbits around the Sun, I gather that its tail loses mass due to solar wind and tidal waves. Approximately, from what distance (with respect to Sun) will the mass loss begin?