# All Questions

7,239 questions
43 views

### Moon's path as seen from Earth

As observed from the surface of Earth: Will the moon ever repeat the same path (trajectory)? If yes, what is the period of repetition? And also will the moon cover the night sky with its path ...
21 views

### Counting stars in a given area

Suppose that, at a distance of 50pc from the Sun, there is a spherical cluster of stars (uniformly distributed) of radius 1pc and that the density of stars in the galaxy is 0.14 per cubic parsec. ...
18 views

### Underground cave in Mars' Armstrong limit [duplicate]

Can a cave, fissure, volcano vent etc. exist on Mars with in the Armstrong limit and support plant life if light and soil was provided? I am not asking how deep is the Armstrong limit of Mars rather ...
171 views

### Why does the Moon appear to be flat?

There's no way around it: when I look at the full moon at night it looks like a mostly flat disc, with at most a bit convexity in the middle. Phases of moon look like a full moon seen through a cut-...
32 views

### Where can I find data on Mercury's orbit to fit a model to? [duplicate]

I have a project in which a Monte-Carlo method is used to find the optimal parameters for some model that is fit to a data set. I want to fit a model for the orbit of Mercury using this methods, but I ...
41 views

### Why is the moon drifting? Shouldn't orbital decay bring it closer? [duplicate]

I noted that the moon drifts away from Earth a few centimeters each year. However, I'm thinking that the emission of gravitational waves would deter such thing and cause the exact opposite. ...
139 views

### A neutron star without a flat surface and an atmosphere?

In the Kurzgesagt video Atoms As Big As Mountains — Neutron Stars Explained they state that neutron stars have an atmosphere that reaches about 10 centimeters above the surface. How is this possible?...
79 views

### Why is the moon that special? Is it really a well built coincidence? [duplicate]

I find it funny that the moon is the only object in the solar system to almost perfectly fit the sun, resulting in the spectacular solar eclipses. No other object except maybe a few irregular moons ...
68 views

### Are red giants stationary or do they move? [closed]

A friend and I are having a friendly chat about this. They are stars so I'm claiming they still move in orbit.
125 views

### How can it be known that Venus does not have plate tectonics?

This answer provides some insight into Venus' surface geology: Water may be necessary as a lubricant for plate tectonics. Whether or not this is the case, Venus does not have plate tectonics. It ...
12 views

### What Would Earth's Mean Surface Temperature Be on Axial Maximum?

Over a 41,000-year cycle, Earth's axial tilt (or obliquity) varies between 22.1 and 24.5 degrees. Both numbers may sound awfully low, but the major benefit that it has for the middle and higher ...
3k views

### Official degrees of earth’s rotation per day

What is the official degree to one decimal point please, of the earth’s rotation in one single day. Can it be confirmed that it is exactly 360.0 degrees using official data? Thank you in advance.
55 views

### Various moon orbits

Orbits can follow certain patterns, as I am aware. Some include a circular orbit around the bulk of the planet, a polar orbit spinning about the pole... What I'd like to know, for a planet with two ...
60 views

### Was is the angle needed to see a glory (a rainbow-like effect) from space off the Earth? [closed]

What positions would the Earth, Sun and viewer need to be to see a glory (a rainbow-like effect) from space? What position would they need to be in to reproduce this picture? Source: Gizmodo (NASA ...
59 views

### Why do planets and satellites in the Solar system look so wildly different if they came from more or less the same matter?

First, the planets. We have Mercury, which is rocky, no atmosphere. But then we have Venus, which is completely different: thick atmosphere, very hot, geologically active. Then Earth - blue, full of ...
95 views

### Why Venus evolved so differently from Earth?

I read somewhere that the reason why Venus has a runaway greenhouse effect and Earth doesn't is the former's inability to form separate tectonic plates due to slightly higher temperature softening the ...
46 views

### calculating stellar visibility

Please could you let me know a (basic) formula for calculating at what time a star would become visible of an evening in clear weather conditions. I presume the formula would involve the stars ...
40 views

### Mini disk of a blackhole meaning

What is meant by the "mini disk" of a blackhole? Is it the same as accretion disk? If not, whats the difference? Eg: In the abstract of this paper https://arxiv.org/abs/1806.05697 it is mentioned "...
147 views

### Does matter accelerate to the speed of light as it approaches the singularity?

$$v_\mathrm e=\sqrt{\frac{2GM}r}$$ If we understand the escape velocity to be the speed needed to escape from the 'surface' of a gravitational object described by the above equation. It is equally ...
88 views

### Can the Sun pull an iron asteriods in it's orbit into it? [closed]

Can our Sun's magnetic field strengthen in any way in a short period? Can the Sun pull anything trapped in close orbit around it? What would happen if an object in orbit passes over a sunspot for ...
58 views

### Have any more “white dwarf pulsars” been discovered or searched for?

Back in 2016, Marsh et al. reported that the binary system AR Scorpii exhibits complex radio signals similar to those observed from traditional pulsars. In particular, pulsed synchrotron emission ...
95 views

### Anti matter in Jupiter magnetic field?

My question is based in this Wikipedia article about the Jupiter magnetic field: https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter Jupiter magnetic field generates plasma and accelerates ionized ...
78 views

### When would we detect a tiny meter size natural satellit in a geostationary orbits?

A natural, tiny (meters-size, maybe 10.000kg mass) natural satellite could be trapped in a geostationary orbit. I wondered for quite some time: When and how are we able to detect these satellites? ...
59 views

### Making sense of the lomb-scargle periodogram

I am trying to use the periodogram to tell when a signal is periodic or not by following the tutorial for the astropy Lomb-scargle periodogram here. http://docs.astropy.org/en/stable/stats/...
58 views

In this paper, Section 2.1, the authors talk about using the ICRF2 to find a tuning frequency in search of the 21-cm absorption (of HI). Since we already know the frequency of HI (1420.40575177 MHz), ...
64 views

### Conversion factors for flux

I have a flux value in the infrared band of 8 mJy at a wavelength of 80 microns that I want to translate into X-ray conventional ...
178 views

### Is the moon inside earth’s atmosphere? If so, what are the consequences?

Recently, a paper was published claiming that the Earth’s atmosphere extends far beyond the Moon. This has been reported on by a number of news sources and websites, including the ESA, Business ...
39 views

### How did the Big Bang occured if before that there was no time? [duplicate]

I am thinking, that if the Big Bang created time, it implies that before the Big Bang there was no time (correct me if I am wrong). My question is that, if there was no time before the Big Bang, how ...
31 views

### Higgs field interactions in universe [closed]

Is the Higgs field found everywhere? Is it responsible for our mass, and are we in the Higgs field?
14 views

### Did OSO-3 or any other spacecraft or ground telescope record the solar activity that is likely the cause of the May 1967 aurora?

The question What solar event caused massive aurora borealis in the mid 1960's? reminds me again of a stunningly bright aurora that I saw circa 40°N circa 1967, and after reading the comments and ...
75 views

### Did I see the dragon capsule on Friday night?

I live just south of Sydney Australia, and I went outside to watch the ISS pass overhead on Friday night. The ISS was following a smaller object easily visible to the naked eye. Sydney time 20.43 or ...
2k views

### Can we track matter through time by looking at different depths in space?

If we look back far enough we can see all the origins of the universe, so is it possible, even if not feasible, that we could trace the history of some matter as it moves through space-time? I want to ...
51 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 ...
46 views

### Mass of a potential black hole in a binary system

So I've been given the velocity curve, parallax and apparent magnitude of a star in a binary system with what is potentially a black hole. I've calculated from the apparent magnitude and parallax that ...
67 views

### How to calculate declination of Moon?

Is there any way to calculate declination of Moon for any day?I'll subtract inclination of Earth on the ecliptic from the result. I'll get Moon's the shortest angular distance from Sun. Thanks for all ...
245 views

### Could Mars have oil?

What events could have to happen to Mars (which is thought to once look like Earth) that may have depleted the atmosphere and erase all proof of life ever existing at least on the surface? I know an ...
58 views

### What fills the new space created during expansion?

Does it remain void and pushes even more or will virtual particles eventually create normal matter?
59 views

### Can a frost line exist around a protoplanet?

The Frost line is the border that marks where volatiles such as water, methane, ammonia, etc. (commonly referred to as 'ices') are able to condense into solid grains in the protoplanetary disk around ...
25 views

### Vertical speed vector at which the sun travels to and from the galactic equator

What is the speed of progression of the sun toward and away from the galactic equator during its orbit?
36 views

### Definition of the light that is projected by a celestial body/luminary [closed]

I'm creating an application which will simulate the light created by sun or moon on a 3d topographic map of Earth. Something like this: Is there a word or definition for this light/light projection?
87 views

### Determine distance from the galactic center in DS9

I have a list of coordinates of black hole/neutron star systems in decimal degrees (ie. {(266.416,-29.009), (266.418,-29.009),...} from DS9 and would like to determine the distance from SgrA* in ...
148 views

### What was the first astronomical measurement which demonstrated that “the Earth is surrounded by vacuum”?

The question Who was the first to realize that the Earth is surrounded by vacuum? was closed because some users felt it was answered by answers to a different question in an different SE site: Who was ...
55 views

### What causes hot temperature extremes?

Recently I looked into the hottest(and coldest, but in another question) natural places. I find this to be a "cloud of searing gas that is surrounding a swarm of galaxies clustered together five ...
54 views

### What causes cold temperature extremes? [duplicate]

Recently I looked into the coldest(and hottest, but in another question) natural places. I discover this to be the Boomerang Nebula, with a freezing temperature of about −272.15 °C. Then I looked at ...
163 views

### Existence of planets larger than their host star?

The mass region of objects between ~ 0.5 Jupiter masses and 80 Jupiter masses (gas giants through to brown dwarfs and red dwarfs) is typified by an almost flat relationship with object diameter. There ...
71 views

### Terminology for empty space at the edge of the observable universe?

Is there a name for a point at the edge of the observable universe at which there is no visible matter, that appears completely dark? I'm thinking something like "empty space", but that could equally ...
57 views

### Is there any positive N on which it's agreed among astronomers that 10^-N is accepted as 0 (zero)? [closed]

Is there any positive N on which it's agreed among astronomers that 10^-N is accepted as, or treated as 0 (zero)? I think one of the sciences that most precision is required is astrophysics. I'm ...
148 views

### Where is the North of the Universe

Does it exist North of the Universe? (Which is probably used for determining coordinates of far galaxies.) If so, then where it is? On what is it aligned? (Is it orientated on Earth, Sun, Milky Way, ...