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7
votes
4answers
900 views

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 ...
-2
votes
1answer
42 views

Data in measures paper

What do this data mean please? http://cdsads.u-strasbg.fr/cgi-bin/nph-iarticle_query?1904AnOBN...8a...1N&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf
0
votes
1answer
64 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.
2
votes
2answers
96 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 ...
3
votes
0answers
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 ...
2
votes
0answers
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 ...
7
votes
2answers
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?
2
votes
1answer
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
21
votes
2answers
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 ...
2
votes
1answer
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 ...
2
votes
1answer
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 ...
3
votes
0answers
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 ...
5
votes
1answer
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 ...
4
votes
1answer
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 ...
10
votes
3answers
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 ...
1
vote
1answer
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): ...
2
votes
1answer
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. ...
3
votes
1answer
105 views

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 ...
4
votes
0answers
40 views

What are realistic and unrealistic values for the high energy gamma ray spectral indices of pulsar wind nebulae?

This summer, I was working on a project fitting very high energy gamma ray spectra of the Crab Nebula, a pulsar wind nebula. At energies about $\sim$1 TeV, a simple power law suffices, i.e. $\phi(E)\...
1
vote
2answers
559 views

I need help using this telescope!

The telescope I'm using is a National Geographic 76 Diameter, 700 focal length, Equatorial Mount. It's hard to use the equatorial mount, as this is my first telescope it's hard to use. Everything I ...
6
votes
1answer
361 views

How is it ensured that a parabolic shape forms while polishing a telescope mirror?

I understand polishing the mirror with a successively finer abrasive can create a curvature, but how is it possible to obtain a uniform curve that forms a parabola while polishing by hand?
3
votes
1answer
98 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!
48
votes
5answers
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'...
10
votes
1answer
375 views

How did they make a video of the center of the galaxy, and what is it exactly that's flashing there?

The ESA video ESOcast 173: First Successful Test of Einstein’s General Relativity Near Supermassive Black Hole includes a clip of images of stars at the center of our galaxy orbiting around SgrA*, a ...
2
votes
1answer
34 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 ...
1
vote
0answers
25 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?
15
votes
2answers
161 views

How can we detect water on Mars-like exoplanets?

According to data from Curiosity, Mars' dust holds about 2% water by weight This wasn't previously detected, so the impression we have had of Mars being incredibly dry may need to be altered. Okay it ...
36
votes
2answers
35k views

How does neutron star collapse into black hole?

We know the spectacular explosions of supernovae, that when heavy enough, form black holes. The explosive emission of both electromagnetic radiation and massive amounts of matter is clearly observable ...
4
votes
0answers
80 views

How does the orbit of a 2-body system evolve as it orbits a more massive 3rd body?

I have been reading up on how multiplicity of star systems decline with star mass, which implies a relatively common occurrence of binary star systems orbiting more massive stars. I would imagine this ...
0
votes
0answers
34 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 ...
12
votes
1answer
953 views

Will LSST make a significant increase in the rate of astronomical event alerts?

The NPR news article and podcast New Telescope Promises To Revolutionize Astronomy updates the status of the "Large Synoptic Survey Telescope under construction on Cerro Pachón in Chile". NPR's Joe ...
6
votes
4answers
905 views

What is the proper interpretation of a negative parallax?

The Gaia data release 2 dataset has some parallaxes listed as negative. What is the proper interpretation of this? Should they be discarded as bad data? Use their absolute value to calculate the ...
10
votes
1answer
200 views

What object in the universe is most opaque to neutrinos?

I had this thought, and my first guess was "high density = lots of absorption, so I guess it's neutron stars" but this physics.se question about that has a great answer which covers why that's ...
2
votes
0answers
34 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?
8
votes
1answer
112 views

What percentage of Helium-3 is primordial vs produced in stars

I tried to research but what I found is pretty limited. A very tiny but non zero percentage of primordial matter was Helium-3 or 3He. Stars produce 3He as part of the proton-proton chain but they ...
1
vote
2answers
59 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 ...
1
vote
4answers
961 views

Can satellites travel in clusters?

Last night we saw a large cluster of what looked like exceptionally bright stars that moved, as a group, across the night sky in Lancaster, PA. It was about 9:15 pm, and they moved roughly from SW to ...
3
votes
3answers
118 views

How many asteroids are named after musicians? Is there a searchable list for this?

Spot checking Wikipedia, Google and JPL's Horizions I found several musicians right away, including Lou Reed, Elvis, Freddy Mercury, and David Bowie. Is there a way to find all of the asteroids that ...
10
votes
1answer
6k views

How does the Moon look like from different latitudes of the Earth?

I have heard, that on the northern hemisphere, you can estimate a direction of south if you imagine a line going through the tips of the border between illuminated and shadowed part of the Moon, and ...
2
votes
1answer
83 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 ...
3
votes
1answer
95 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 ...
2
votes
1answer
50 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 ...
0
votes
1answer
57 views

About Radius and Surface Area

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 ...
5
votes
1answer
74 views

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 ...
1
vote
0answers
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 ...
4
votes
3answers
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 ...
2
votes
0answers
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 ...
-2
votes
1answer
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
3
votes
3answers
147 views

Plant on large Asteroid?

I'm just curious if it is possible for a plant to survive on a large asteroid. Some say no, some say it depends. With the scenario of an asteroid at about 1 AU from the Sun, receiving a similar ...
4
votes
4answers
866 views

So where are these measurements of galaxies moving faster than light?

https://physics.stackexchange.com/questions/400457/what-does-general-relativity-say-about-the-relative-velocities-of-objects-that-a "we can actually observe galaxies that are moving away from us at >...

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