# All Questions

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3 views

### Get a table of moon phase angle per day

Where can I get a table with the moon phase angle for each day ? It's availble here for a given day, but I'd have to input each day of a year to get a full table.
29 views

### How much volume of gases could be added to Mars atmosphere that the planet gravity can retain?

This article Mars atmosphere states that Today Mars atmosphere is very thin, but it was not always like this. Around 3.5 billion years ago, the red planet had a thick enough atmosphere for liquid ...
29 views

### Formation of the First Stars

I've got a few questions about the first stars to form in the universe. First off how might metalicity have impacted the formation of the first stars and also what effect would the absence of metals ...
950 views

### Is it possible that the shadow of the moon is a single dot during solar eclipse?

During a solar eclipse the moon covers the sun on some places on the Earth. Now the focal point is a bit above the Earth so the shadow area is about 160 miles. In history the moon was a bit closer to ...
44 views

### Cosmological redshift vs doppler redshift

I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift. He ...
53 views

### What is a black hole's “shadow” and the best angle to view it to measure the spin?

This excellent answer mentions several ways to try to observationally measure the spin of a rotating black hole. The third one is intriguing, but I don't understand how this works: The spin of a ...
133 views

### When did people discover that the Earth is not an ideal sphere, but a little flattened?

When did people discover that the Earth is not an ideal sphere, but a little flattened? And if you know, who was the first person to discover it?
15 views

### Dispersion: any software to work out the dispersed waveforms of EMW signals that propagate via interstellar medium for some distance?

Is there any software (toolbox, code, package, paid or opensource are both ok), to work out the dispersed waveforms of EMW signals (time series data are given), that propagate via the interstellar ...
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### Does the Sun have a numerical designation in any star catalogues?

Given the existence of large star catalogues listing millions of astronomical objects with numerical designations (such as Tabby's Star, KIC 8462852) it occurred to me that one of them might contain ...
132 views

### Can we see evidence of sunspots on other stars

Searching for exoplanets by measuring the change of a stars brightness when an exoplanet transits the star's disk also has the potential to detect exo-sunspots. Have they ever been detected?
33 views

### Estimate prevalence of ʻOumuamua-style interstellar obects inside Jupiter orbit now that C/2019 Q4 (Borisov) is found?

Now we know two of them, so maybe it's not an outlier. We have two points so we can draw a line. How many similar macroscopic objects should be zipping through space at ~30 km/sec so that we would ...
17 views

### Redshift, velocity, distance

How are redshift, (recessional) velocity and distance of a galaxy related? I understand what v=HD states. So I assume that Hubble measured a direct relation between the distance and recessional ...
546 views

### Can I see Harvest moon in India?

I just saw articles which say the Harvest moon will be visible in the US. Apart from the US, in which other country can people see it? Can I see it from India?
11 views

### How to model and subtract nebular emission lines from stellar spectrum

I have optical stellar spectra from a star forming region with spatially varying nebular background. I want to subtract the nebular lines from the stellar spectra (which are varying in intensity from ...
33 views

### Any night sky image databases

I was wondering if there were any available databases for photos of the night sky. It doesn't have to feature pictures of any particular star, just has to be a large collection of photos from the ...
3k views

### How do we know that black holes are spinning?

How is it possible to know if a black hole is spinning or not? If a planet is spinning, you can see it clearly but you can't really see a black hole. Next thing would be that matter interacts with ...
62 views

### Storm on Earth vs. storm on Jupiter?

Why is the storm on Jupiter much stronger than storms on Earth and why don't the storms on Earth get as big as Jupiter's great red spot
33 views

### Why does the outside edge of a Kerr black hole ergosphere rotate at the same speed as the inner edge?

Reading through the Wikipedia on a Kerr black hole ergosphere, and this nice question on the maximal spin rate of a black hole leads me to ask: why does the outer edge of the ergosphere rotate at the ...
75 views

### What makes scientists already so certain that Comet C/2019 Q4 (Borisov) is a comet and not an asteroid?

US Naval Research Laboratory scientist Dr. Karl Battams has recently tweeted Unlike 'Oumuamua, whose asteroid-or-comet nature still gets debated, this one is definitely a comet. If it is ...
55 views

### How to derive the date (day, month) from the day of year? [on hold]

Is there any formula to derive date from day of year? Say I want to know the date of 255th day of 2019. That is 9/12/2019.
52 views

### Sky from Equator at 8,000 years Before Present?

The Stellarium software allows future views of the sky. I need an online resource (planetarium projector?) that shows pre-historical views, and from the Equator at 8,000 years before the present.
78 views

### Would two Earth-like planets on opposite sides of a Sol-like star at about 1 AU be a stable configuration?

Would two Earth-like planets on opposite sides of a Sol-like star at about 1 AU be a relatively stable configuration? I understand that there are tadpole-like orbits and the two planets may not stay ...
40 views

### What is the intensity distribution of visible light over the solar disk?

What is the distribution of the visible spectrum over the solar disk? Images of the Sun using the visible spectrum suggest that the light emmitted from the edge is almost equal to the light emmited ...
34 views

### Gravitational lensing

I was reading about gravitational lensing. I was just curious to know if there are any formulae or methods to find the angle at which the light deflects due to strong gravitational lensing? And how ...
21 views

### Angle of the Sun during winter solstice

What is the angle of the Sun on the eastern horizon at 35° latitude if it is the winter solstice?
101 views

### Why is this telescope so short? How hard is it to make such a fast primary?

The recently discovered object C/2019 Q4 (Borisov) is in the news because it might have an eccentricity greater than one, which means it might be from outside the solar system, though not necessarily. ...
25 views

### What equipment do I need to measure the spectrum of a star?

For an amateur astronomer, is it possible to measure the spectrum of a star? I can easily take a photo of a star just by putting a camera on one end of a telescope and over exposing it. But I would ...
32 views

### Do we know what happens at the boundary of the universe, what are some theories about it? [duplicate]

Do we know what happens at the boundary of the universe, what are some theories about it? Does space time differ at the boundary? Do things become larger at the boundary? Do the trajectories curve and ...
117 views

### What is the size of the largest asteroid orbiting the Earth, other than the Moon?

It seems odd to me that no other asteroid around the Earth is even close to the size of the Moon. Anyone have any idea about the size and orbit radius of Earth's "second moon" ?
32 views

### Syncing time for measuring the parallax of Mars

I read somewhere (I can't remember the website) that when Cassini and Jean Richer measured the parallax of Mars, they used Jupiter's (or maybe Saturn's) moons to sync their time. How was this done?
99 views

### Is every star formed in an open star cluster?

As far as I understand, an open cluster is formed from a single molecular cloud, with each star in the cluster having roughly similar age and properties. Our Sun is not part of any star cluster, but ...
83 views

### Where would an object fly to if it were to leave the gravitational field of Earth? And would it stop somewhere? What would happen to it?

My 3,5 year old son is asking :-) He can take answers for a 15 yo I think. Many thanks for your help!
49 views

### What parameters cause sunburn? [closed]

I am new to this site so if the question doesn't fit in this forum feel free to remove it. I have read here https://en.wikipedia.org/wiki/Sunburn of all the causes of sunburn and I was mostly aware ...
134 views

### What will future populations of stars be like?

As stars slowly using up hydrogen and ejecting heavier elements into space, the future stars will form from nebulae that are more metal and helium rich. The question is: how does the increased ratio ...
35 views

### Can the electric field of the Earth's be used for satellite maneuvering? [migrated]

Is it feasible to create a strong dynamic dipole inside a satellite so that it can be rotated on its axes and even possibly pushed in a direction due to the Earth's Normal Electric field. This might ...
90 views

### When are the symbols ⊕ and ♁ used to designate Earth?

In astronomy I usually see Earth designated with a circled plus or cross. NASA says this is the Earth's astronomical symbol. Wikipedia tends to use it, for example designating the Earth–Moon distance ...
43 views

### Perihelion dates and parameters

I have to find the perihelion and aphelion data for the 20th century for Earth. I found this table http://www.astropixels.com/ephemeris/perap2001.html, but no such table for the past century. I ...
75 views

### Why does nobody ever consider the possibility that the universe is not smooth? [migrated]

Disclaimer: I'm not an astronomer, physicist, mathematician, etc. so this is a question from a complete newbie. One of the greatest mysteries of our age is "where is the dark matter?" The universe ...
54 views

I am researching about the radius of a star and a its surface area. One question I have is about the effect of changing radii in stars. If for example we have one star with radius $r$ and another one ...
49 views

### How to apply Fast Folding algorithm?

I have High Time Resolution Universe dataset. I have applied de-dispersion on this HTRU dataset, and thereafter I applied the folding function to fold the dataset. How I can find that the periodicity ...
9k views

### Is there a star over my head?

Say I'm standing up straight, and I draw a straight line from my core through the top of my head (perpendicular to the ground). What is the probability that that line intersects with a star? EDIT: I'...
41 views

### Right Ascension, Declination from pixel coordinates

I have an Excel spreadsheet that will take certain keywords from a FITS image header. Image centre RA, Dec, rotation, x centre, y centre, x scale, y scale. I enter the pixel coordinates of an object ...
47 views

### What is the physical reason of the mirror principle in the stellar evolution?

I understand that stars transition into the red giant phase by obeying the mirror principle, as written here: Shell-burning stars obey something called the mirror principle, which is an observation ...
80 views

### By convention, when observing an exoplanet, is the observer's line of sight (on Earth) perpendicular to the plane of sky?

This is just a quick question. In this picture of the orbit of an exoplanet, is the observer's line of sight perpendicular to the plane of reference, which is in the +z direction on the diagram? In ...
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### Any simple experiment with an H-alpha telescope?

Is there any simple experiment that can be done with an H-alpha telescope, for example to estimate the Sun's mass, size, distance, temperature or intensity? I give lessons about renewable energy and ...
37 views

### GPS Constellation Explanation [closed]

I have been reading about GPS lately, and keep encountering the same details. There are 6 orbital planes, each at an angle of inclination to the equator of 55 degrees. The 6 orbits have in each of ...
37 views

### Space expanding not valid [duplicate]

I believe the bigbang theories theory of universe expanding does not hold good for entire space because space is infinite and there is no central point for space. Am I correct, plz comment.