5
votes
1answer
72 views

Was the use of silver on 'optical' telescope mirrors more common in the past? Why?

In the past, weren't many astronomical telescope mirrors periodically removed and 'resilvered', and wasn't this actually done using silver? I'm guessing that this is much less common now - new ...
1
vote
1answer
65 views

UTC to UT1 time corrections

Astronomic observations in geodesy. It is well understood that sun and star positions may be expressed in Greenwich hour angle and declination. Or Right Ascension Declination. And may be published ...
1
vote
1answer
205 views

Could a cross-ringed planet exist?

My title doesn't do my question justice in explaining, but the kind of satellite system I'm thinking of is two rings on two separate axis, much like (if you've seen it) the film 'Treasure Planet' ...
14
votes
2answers
223 views

Why do we believe that the super massive black holes at the centers of two merging galaxies would themselves merge?

When listening to podcasts or watching youtube videos of astronomers discussing galaxy mergers, I often hear talk about how the super massive black holes at their centers will themselves merge during ...
3
votes
0answers
40 views

Why do so few satellites pass over the poles, and why do so many focus on the equator? [migrated]

The following screenshots from the website Stuff in Space, which tracks satellites and man-made debris orbiting the earth show us a few things: Very few satellites (or pieces of debris) pass over ...
0
votes
1answer
38 views

Why aren't planetary bodies static? [duplicate]

Why are planets moving in the first place? Gravity causes them to orbit, but why move at all? note: this is not a question on why planets orbit each other, I know the reason for that is gravity. ...
1
vote
2answers
54 views

What is the most distant observable White Dwarf known?

I attended a talk last week about Type 1a supernovae with the focus being on double-degenerate systems as potential progenitors for them. We were shown a graph of White Dwarf (WD) mass distribution ...
5
votes
2answers
225 views

How Does Black Hole Evaporation Look From the Inside?

Imagine you're inside a black hole event horizon. The curvature of spacetime is such that the direction towards the singularity becomes timelike, as reverse movement becomes literally impossible. How ...
-1
votes
1answer
62 views

What are the small things, look like stars, moving in the sky? [duplicate]

I have always been observing something that looks like a star but not as bright as a star moving from south to north at the same time every night. What is it? It cannot be a star because I know ...
0
votes
2answers
178 views

Question about space-time

In the Big Bang model of the Universe, every observable thing is thought to have expanded very abruptly from a point of infinite density and zero volume. However, the problem with this assertion is ...
1
vote
0answers
64 views

What is the shape (along the plane, not up-down) of stellar orbits in flat spiral galaxies

What I mean is, with a central mass orbits are relatively simple, but orbits around the galaxy are different, in essence as the star orbits through the dark matter halo, the further it moves away from ...
0
votes
2answers
60 views

Kepler's second law of motion

Planets sweeps out equal areas in equal times. Is the area being calculated here the area of a triangle? You draw a straight line from the center of the sun to the earth at point A. The Earth moves ...
9
votes
2answers
1k views

Why does Titan's atmosphere not start to burn?

If Titan has a methane atmosphere and seas of methane, then why doesn't some meteoroid / chemical reaction ignite and blow the whole thing?
14
votes
6answers
3k views

Is the light we see from stars extremely old?

Our nearest star Proxima Centauri is 4.243 light years away from Earth. Does that mean we are seeing light that is 4.243 years old everyday?
1
vote
2answers
63 views

Can a tidally-locked planet maintain an obliquity

If a planet is tidally-locked, can it have an obliquity? e.g. the Earth's rotation is being slowed by tidal forces. A long way in the future it will be tidally locked. As it slows, will the ...
1
vote
1answer
71 views

uses of coordinate systems

Wikipedia describes the five following celestial coordinate systems each with rectangular/spherical variants: horizontal equatorial ecliptic galactic supergalactic What are the practical preferred ...
1
vote
2answers
90 views

Which stars do I have to use to join with a line to draw constellation?

I continue working on a planetarium software and I want to draw the lines that the draw the constellation's figure: Is there a catalogue or something similar with the stars which are the vertex of ...
1
vote
2answers
31 views

lunar calendar accuracy for predicting new moons

I wonder, how accurate the lunar calendar is? Can we predict the new moons precisely for tens of years in future? If we know all factors that affects the movement of the moon, then why it is not ...
0
votes
2answers
62 views

Data reduction and photometry without IRAF?

The IRAF package is old. I've been looking around for a more modern software to replace it in the processes of CCD data reduction and photometry, but haven't been able to find any. The closest I've ...
1
vote
1answer
82 views

How massive can a cold solid object be?

I understand that a neutron star is dense enough that adding more matter will increase the amount of degenerate matter directly, and the limit to its size is about 1.4 solar masses. But if an object ...
1
vote
1answer
67 views

Eclipse — Solar and Lunar

Q. Why is solar and lunar eclipse not seen from all parts of the earth at the same time? I think its because of the revolution of the earth but i am not sure. I want a more reliable answer.
1
vote
1answer
18 views

Future redshifting and effect on the 'pitch' of CMB radiation

After discovering this question exploring the sound of a blackbody, I started wondering about the sound of the Cosmic Microwave Background radiation from the Big Bang, specifically what the current ...
3
votes
1answer
98 views

What may be the period and speed of revolution of the star that is closes to galactic centre?

The Sun moves at the speed of 220km/s around the galactic center in a circular orbit. The sun is located at about 30,000 light years from the galactic center. The Sun orbits around the center of the ...
4
votes
3answers
1k views

Why doesn't the sun pull the moon away from earth?

If the suns gravitational pull is strong enough to hold much larger masses in place (all the planets) and at much greater distances (all planets further away from the sun then earth) why does it not ...
0
votes
1answer
49 views

How to calculate the pixel size and beam size of an image?

I have an image with some sources in it. I need to get the pixel size and beam size of that image. How can I calculate it?
3
votes
2answers
249 views

Apogalacticon and Perigalacticon

What is the length of the apogalacticon and perigalacticon of the Sun and Milky Way? The general terms seem to be apoapsis and periapsis. My greatest efforts at Googling have failed miserably. If ...
1
vote
1answer
56 views

Why aren't stars like Eternally Collapsing Objects?

We know that stellar radiation pressure balances the gravitational compressive forced of a star. Are there other factors which resist such a collapse? Also, if radiation pressure balances ...
2
votes
1answer
99 views

Finding a location using the direction of shadow, UT and date approximately

Does anyone know how to find a location by using : the direction of shadow relative to the normal (for example azimuth angle) the Universal time (UT) and date I have a satellite image and I know ...
3
votes
1answer
81 views

Solar / lunar positions in ECEF using SOFA C libraries

I'd like to calculate the positions of the sun and moon in the ECEF coordinate system using the SOFA (http://www.iausofa.org/current_C.html) libraries given a Julian day input. So far, I've got this ...
3
votes
2answers
3k views

What will happen when landing on Jupiter?

Jupiter is a gas giant, so landing on it will not be like as on Earth, our moon or Mars etc., as it does not have a solid surface like these. If we have a hypothetical spaceship or probe landing on ...
11
votes
1answer
616 views

How many galaxies disappear beyond the Hubble Bubble horizon every year now? [duplicate]

The accelerating expansion of space means that the space between us and far away galaxies expands faster than light can travel through space. There is a horizon of possible observation beyond which ...
2
votes
1answer
114 views

Has the velocity of photons coming from black holes already been measured?

Has the velocity of photons, which are coming from black holes, already been measured? I am not aware of such measurements. The reason for the question is the following: If space-time near black ...
1
vote
3answers
263 views

Oldest in the universe

When the big bang happened and all that exist today came into existence from singularity, how do you determine which part of the universe is the oldest? Its natural to think that looking back at the ...
0
votes
3answers
62 views

Are we moving faster than the Cosmic microwave background radiation?

if the Cosmic microwave background radiation is coming towards us in the speed of light and all matter and energy was singular at the big bang, doesn't that mean we somehow moved faster than the speed ...
0
votes
2answers
504 views

Do planets repel?

I know gravity is the result of mass. Gravity is nothing but the attractive force on a body due to its mass. I have a question that may be silly. In magnetism we have attraction and repulsion. Earth ...
5
votes
3answers
166 views

How fast would Earth need to rotate to fling someone off due to centrifugal force?

If Earth started spinning fast enough, would the centrifugal force eventually overcome Earth's gravity enough enough to fling someone (let's assume 75 kg) into orbit or into space? If so, how fast ...
0
votes
1answer
47 views

Inverse of the sunrise equation - finding locations with a given sunrise time on a given day

I'm working on a project for fun where I represent some sleep data geographically. For a given day, I have a date, a time for falling asleep that night, and a time for waking up the next day. The idea ...
0
votes
2answers
134 views

Term for altitude of the sun?

The sun travels in an arc across the sky. Where I live, during the summer the arc rises higher, but in the winter the arc is lower. Once might speak of highest altitude or elevation the sun reaches ...
0
votes
1answer
29 views

The Three Elements in the Milankovitch Cycles

According to the Serbian geophysicist Milutin Milankovitch, there are three elements that make an ice age possible: Eccentricity (orbital shape): Varying between 0.000055 and 0.0679 over the course ...
1
vote
2answers
166 views

Has NASA confirmed earth now has a second moon orbiting the planet?

Several sites claim NASA has confirmed a second moon orbiting earth. This is the Asteroid 2016 HO3. One source states The newfound quasi-satellite/moon-2016 HO3, is likely larger than 120 feet (40 m) ...
1
vote
1answer
50 views

What solar features would I see at 10x magnification?

I have a pair of binoculars with 10x magnification, 50mm objective diameter, and 6.5 degree (real) angular field of view. I'm looking into buying solar filters for it (something like these) so I can ...
0
votes
1answer
59 views

Could dark matter be “inside-out” reality?

Where we are, and in the conventional galaxies etc. that we see, there is a whole lot of relatively uniform space but in isolated places within that space, there are pockets of concentrated "mass" ...
0
votes
1answer
48 views

Would we be able to feel the acceleration of a planet with a highly eccentric orbit?

Even though our Earth moves on average 67,000 miles per hour around the Sun, we cannot feel its movement since its speed is fairly constant. More precisely, its change in speed is very low and our ...
0
votes
1answer
41 views

Converting ångströms to km/s

I have a spectral cube (in FITS format) whose spectral dimension is in ångströms. The sampling along the spectral dimension is 0.28A (CDELT=0.28). The observation in the cube is Ha emission of a ...
1
vote
4answers
133 views

What are the exact causes that differences in sunrises are shorter around june and december but long in march and september?

The changes of the sunrise and sunset times not expire regularly in a straight line but according to a sinusoid. Around the solstice (summer solstice on June 21st and winter solstice on December 21), ...
2
votes
0answers
50 views

Juno Mission. How better resolution will the optical images be to previous missions? [migrated]

Resolution in km/pixel at: (i) the closest approach and (ii) typical when in close to Jupiter part of the eccentric orbit.
2
votes
2answers
88 views

What color is earthshine?

What color is earthshine (e.g the average color of earth that shines on the moon)? I am making a solar system exploration game, and would like to know this for the lighting of my moon level at night, ...
1
vote
2answers
138 views

Color of planets

I am developing an astronomy software and need to know the color of each planet in the Solar System, when observed with the naked eye. I cannot find that information after googling for a while. Is ...
1
vote
1answer
61 views

K-Pg asteroid impact

Is it possible to determine what daytime the Chicxulub impactor striked the Earth 66 mya? Was it day or night, what was the current phase of the Moon etc.? Can sediments, rhytmites or something else ...
3
votes
4answers
135 views

Would space-based telescopes need to remain in the shadow of Earth to avoid light interference from the sun?

So I am thinking about orbiting telescopes tonight and I was thinking that it would probably be beneficial to keep them in the shadow of the Earth or some other space body to avoid light interference. ...

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