# All Questions

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19 views

### Using a differential force in the derivation of hydrostatic equilibrium in a star

I've been banging my head against this particular derivation of hydrostatic equilibrium in a star for the last few days, from Carroll and Ostlie's Introduction to Modern Astrophysics (2nd ed. p. 286): ...
10 views

### A question about stress energy tensor at junction surface

I am now reading a paper (whole paper link)which regarding construct a worm hole by cutting off the stress energy tensor and glue interior and exterior space at $r=a$. ‘Nevertheless, I am confused ...
42 views

### Could Planet Nine be much smaller than thought previously?

In 2016, Caltech astronomers began testing a Planet Nine hypothesis to explain the eccentric and inclined orbits of distant dwarf planets such as Sedna, 2015 TG387, Niku, and 2012 VP113. The ...
26 views

### Looking for Solar Analemma visualization with variable orbital elements for Earth

I've found some flash animations for the Solar Analemma where I could change parameters such as latitude of observer, and I could see the resulting effect on a 3D image. This is it: http://astro.unl....
57 views

### In binary systems, does the speed of the objects vary as they adjust to the movement of the other object?

The speed of objects orbiting in a binary system, like Pluto and Charon, is the speed and direction of the objects smooth, or, do the objects make adjustments that are in some ways like a "tug of war" ...
36 views

### Scale factor 0 for expanding universe

Does the FLRW model have a scale factor $0$ at the singularity, meaning that even infinite distances become $0$ there according to the mapping $x \mapsto a(t)x$, for $a(t)=0$? I am asking this ...
25 views

### Article - how does interstellar extinction (dust) influence spectra?

could you recommend me a scientific paper about how does interstellar extinction (dust) influence spectra? I tried SAO NASA ADS but I didn't find anything. Thank you
68 views

### Do planets orbit the sun in ellipses because of sun movement vector?

The assumption is made that the planets of our solar system all have elliptical orbits elongated in the same direction. Further, generalized to that orbits around any object with its own orbital ...
44 views

### Would this movement vector for our solar system cause a “barycenter” orbit?

The assumption is made that the planets of our solar system have elliptical orbits because our sun is itself moving with a vector aligned with the ecliptic, causing the circular orbits of the planets ...
19 views

### Research about Light Curves with python

Astronomy is a wide field and i want to do research in it. K2/Kepler and TESS missions has an array of data with light curves. Kepler/Tess --> Extract Light Curve --> Python --> Data Analysis I've ...
779 views

### Could the barycenter orbit of our sun be greatly underestimated?

The radius of the suns orbit around the barycenter of the solar system is often measured to be roughly the radius of the sun. Based on the same type of bias that has made humans miss things about ...
20 views

### Why do CME's “zig-zag” on their way to Earth?

This answer states: A single CME will impact a spacecraft from only one direction, but that direction might not be directly from the sun because a CME may zigzag en route. Looking at that link, ...
43 views

### How do they choose the launch date for interplanetary missions (such as Mars Rover launch?)

I know it involves calculating when the obits coincide but I am wondering if anyone can shed more light on this. Do they launch at the date of the closest orbit, or do they plan for the rocket to ...
24 views

### If interstellar medium was dense plasma and light slowed down, would things appear to move slower far away?

Voyager 2 recently left the solar system and registered an increase in plasma density. If light moved slower in this dense plasma, would it appear like events in other solar systems played out slower ...
156 views

### Difference in gravity on both sides of the moon

How much (if any) difference in gravity would you feel if you are on the surface of the moon and: standing right 'under' earth (exaclty between the moon and the earth) and on the opposite side of the ...
50 views

### Do comet tails increase as comets move away from the Sun?

Do the tails of comets increase on their return trip from the Sun?
25 views

### What are the smallest star clusters affected by Galaxy Rotation Curve?

We all know that Milky Way exhibits Galaxy Rotation Curve which makes it rotate very differently that Newtonian mechanics would expect. But Milky Way is a pretty large galaxy, and the one we only see ...
61 views

### Could a gas giant orbit a star with a 30 year period at a distance of just 1 AU?

Assuming a star with similar properties to our sun, could a gas giant orbit it with an orbital period similar to that of Saturn, but, at a much closer orbital distance, more similar to 1 AU?
34 views

### Are the Leonid meteor storms a thing of the past?

According to the Wikipedia article on the Leonids, "a close encounter with Jupiter is expected to perturb the comet's path, and many streams, making storms of historic magnitude unlikely for many ...
89 views

### What did I see in the sky? [closed]

Last night, my sister a friend and I all noticed a star moving slowly across the sky. I thought it could've been a satellite when I first noticed it. When I mentioned the star to my sister, the star ...
16 views

### Millisecond pulsar timing analysis on fits file

I'm amateur to astronomy and I just want to calculate the spinning period of a pulsar (for example MAXI J0911-655) from lightcurve of it. I found Xamin then I collected data for MAXI J0911-655. Using ...
5k views

### Moon's unusual gravity

We know that the Moon's gravity is about one-sixth that of Earth. Then I recently read that the mass of the Moon is about one-eightieth the mass of Earth. Since gravity depends on the mass of the 2 ...
55 views

### How do I find the signs that planets are in during any given date?

Say for example I wanted to know where the planets were on December 19th, 1664, at 1am; how do I figure that out?
36 views

### How to pick a telescope?

I am trying to find a started telescope for my high school sister and my goals are to have awesome pictures and to let her explore her interest in the stars! They live in a clear night sky area so Im ...
119 views

### What's the point with Hawking Radiation

I saw that Black Holes can evaporate because of Hawking radiation. Because pair of particle, antiparticle can spawn at any point of the space, the antiparticle could be absorbed by the black hole and ...
74 views

### How do I calculate the Hill radius of a star in a binary system?

Is there an easy way to calculate the Hill radius of a star in a binary system at different orbital radii where both stars are of the same mass and in circular orbit around one another’s centre of ...
27 views

### Relation between initial mass and evolutionary phases lifetimes

Consider the following image (Source: An Introduction to Modern Astrophysics): There seems to be a relation between the initial mass/mass at the beginning of the MS and the time spent during ...
45 views

### What is the difference between emission line and recombination line?

When an electron jumps from higher level to lower level a photon is emitted. This is seen as an emission line. But what exactly is a recombination line? I found them similar. Can you please tell me ...
49 views

### The brightest star in the Bootes constellation is Arcturus now in the eastern sky [closed]

The brightest star in the Bootes constellation is Arcturus.
79 views

### How many satellites does the Milky Way have?

The small and large Magellanic clouds are galaxies that are orbiting our own galaxy. How many such "galactic satellites" do we know of?
35 views

### How are galactic rotation curves determined from radial velocity measurements?

I have been reading about the deviation of galactic rotation curves from the predicted Keplerian curve to a flat curve at large galactocentric distances. They were the first indicators of the ...
55 views

### Very Old Stars in the Universe [duplicate]

How could a Star possibly be older than the Universe ? Is this possible or are the calculations off when determining the age of such Stars ? Can a Star exist that formed on its own independent of a ...
26 views

### Methods for testing a refracting telescope lens

I have an old (nearly 50 years old)alt-azimuth three-inch (7.6cm) refracting telescope that someone else made. They ground the lens, created the cylindrical body and added a rack and pinion style ...
41 views

### What fraction of galaxies host active galactic nuclei?

I've been saying "some". I can't find a reference for a particular percentage. This seems to address the question to some extent; https://arxiv.org/abs/astro-ph/0108389 would "roughly 1%" be in the ...
52 views

### How can I determine if a typical low-end telescope is a refractor or reflector?

Is there a way to distinguish (with no manual, product info etc)?
31 views

### Position of a star on the HR diagram

Does the position of a star on a HR diagram depend on the magnitude system/color index used? I made a CMD of a particular cluster using HST WFC3/UVIS data, and when I plotted $F275W vs F275W - F606W$...
46 views

### How can I download spectra of planets of the Solar system? [closed]

I don't know how to download data here or there of spectras of exoplanets I want to download it because I want to plot the spectra of various exoplanets and see the difference in their spectral lines. ...
41 views

### Number of actuators in adaptive optics

It is well known that diffraction resolution of a telescope depends on the exterior radius of aperture: One can, for instance, use just a narrow outer ring of a parabolic mirror and the resolution ...
69 views

### What are the benefits of a large refracting telescope?

Currently, refractor telescopes are limited in aperture because gravity will deform the main lens over time. According to Wikipedia the largest practical refracting telescope is 1m. If we were to ...
1k views

### What are optical counterparts?

There surprisingly no proper definition of this term available on google. There are many research papers that are based on "finding the optical counterparts". What exactly are optical counterparts ...
17 views

### Relationship between IMF and time spent during an evolutionary phase

I was reading a little about stellar evolution and was wondering whether there was any relationship between the lifetime of an evolutionary phase and the IMF, I searched on google but all I found were ...
56 views

### Is there a reason two interstellar objects were found in the solar system in such a short period of time?

ʻOumuamua was discovered on October 19, 2017, and 2I/Borisov was discovered on August 30, 2019. Has something changed about observation techniques or equipment that made it possible to find these ...
85 views

### Why does the Supernova 2006cm give a very different value for the Hubble constant? Why doesn't it increase error bars for the Hubble constant?

The Supernova 2006cm has a redshift of 0.0153 which translates into a recession speed of 4600 km/s. It has a distance modulus of 34.71 which translates into a luminosity distance of 87 Mpc. This ...
154 views

### Did nobody in the Astronomy community think 12,000 new satellites in LEO might be a problem?

This answer to Can / should the Starlink satellites be blackened? mentions Space News' SpaceX working on fix for Starlink satellites so they don’t disrupt astronomy where SpaceX chief operating ...
98 views

### At what cosmological redshift $z$, does the recession speed equal the speed of light? How is it calculated?

At what cosmological redshift $z$, does the recession speed equal the speed of light? What equations are used to calculate this number (since at large redshifts, $z=v/c$ won't apply)? [The ...
19 views

### Can mean motion resonances make orbits more unstable rather than more stable?

This paper on closely packed orbit simulation seems to suggest that having the planets in first and second order resonances decreases the time till orbits cross each other. I'd got the impression that ...
42 views

### Relationship between Color Index and Temperature

Is there an exact relationship between color indices and temperature? I have seen some numerical formulas relating B - V color index to temperature, of the form $B - V = a_1 + \frac{a_2}{T}$ . I ...
26 views

### Artificial gravity using Permanent Magnet method [closed]

Is it possible to create an artificial gravity for space station by using floating/rotating permanent magnet the inner floor/living quarters to counter rotate the outer rotating station when creating ...