# All Questions

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### Is it possible to use Hubble Telescope to observe Earth in the past?

We can observe many astronomical objects and structures beyond our solar system, however our observations are as the objects appeared in the past due to the speed of light. My question: "Is it ...
42 views

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### 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.
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### 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 ...
57 views

### 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 ...
35 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 ...
577 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?
91 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
24k views

### Why did Venus not lose its atmosphere without magnetic field?

It is often stated that the magnetosphere not only shields the planet from cosmic radiation, but also prevents atmospheric loss. Why then did Venus not lose most of its atmosphere if it doesn't have a ...
24 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 ...
57 views

### Existence of a mass-volume astronomical chart?

I've been wanting to make a mass-volume (or mass-radius) chart for astronomical objects ranging from asteroids to supermassive black holes on a log-log scale. A sort of 'Hertzsprung-Russel' type ...
40 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 ...
53 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 ...
102 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 ...
911 views

### antimatter annihilation in stars

Electrons annihilate with positrons produced through fusion processes in stars. Which particle interaction produces new electrons so that the sun isn't deplete of electrons? Or is something else ...
4k views

### Calculate Day of the Year for a given date

I am trying to make sense of the following formula that claims to calculate the day of the year given today's date represented by (day/month/year): ...
152 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. ...
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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 ...
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### Textbook to explain measurements and calculations for heliocentric solar system

I'm trying to identify a textbook I had briefly and then lost. I had a PDF file of an astronomy textbook, but the hard drive crashed irreparably before I could thoroughly read the textbook, or even ...
61 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 ...
144 views

### Is Earth's climate significantly different when the one solstice occurs at aphelion rather than the other?

I mean different in some kind of significantlly non-symmetrical way, such as it being much colder during one period rather than the other? Let's assume other factors, such as tilt due to nutation and ...
46 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 ...
145 views

### From what distance will be able to see milky way and andromeda collision? [closed]

Considering that we would out of Milky Way, at what distance would a human will be able to see the collision with naked eye and and how fast would the galaxies appear to be approaching each other