# All Questions

6,952 questions
156 views

### How do we know distant stars still exist

The Pleiades are 450 light years away. Thus when we see the twinkle in the night sky the light that hits our retina emanates from the year 1569 or so. On that proviso; how can we be sure that the star ...
46 views

### What happened to the third planet in the Kepler-47 system?

In 2012, the discovery paper for the multiplanet circumbinary system Kepler-47 mentioned a potential third transiting planet in the system: A 0.2% deep transit-like event is present at time 2,455,...
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### does the orientation of orbital plane of our solar system rotate with the galaxy

As I understand it, our solar system travels through the milky way with the orbital plane tilted about 60 degrees so that we are sort of traveling in the direction of earth's north. My question is if ...
20 views

### Change in axis of the Earth if the Moon would dissappear [closed]

I read that, if the moon would not be there or if it would dissapear or be destroyed it could cause the earth to rotate into a possible axis of 45° degrees. Because it would be missing the ...
30 views

### How many amateur telescopes are looking for serendipity in a coordinated fashion, on average?

I can't read the Nature Astronomy article A kilometre-sized Kuiper belt object discovered by stellar occultation using amateur telescopes because the library I use doesn't subscribe electronically. ...
4k views

### Could stars form outside of galaxies?

Is it possible for there to be a dense enough nebula to form stars outside of any galaxy? Does a galaxy have a minimum size to produce stars? Or could you have a few dozen stars clustered together by ...
22 views

### What is the evidence that the universe began in a hot, dense state 13.8 billion years ago? [duplicate]

What are the evidences to prove big bang theory and proof how the universe began in a hot, dense state 13.8 billion years ago?
73 views

### What causes Titan a moon to have a denser atmosphere than that of a Mars?

I'm wondering about Mars and Titan. If Mars is larger than Titan how come it lost most of its atmosphere? Mars also has a magnetic field while Titan doesn't. Yet Titans atmospheric pressure on the ...
1k views

### Infalling observer could never cross Black Hole event horizon? [duplicate]

I have an interest in cosmology, but I would no way consider myself an expert. It would be great if the more knowledgeable contributors would be able to answer the question I have posed. The intense ...
155 views

### Could a moon orbit an Earth size planet in such a way as to create a solar eclipse lasting for several weeks from start to finish?

Is it theoretically possible for a moon to orbit a planet (let us say Earth size, mass and solar distance) in such a way as to create a planet-wide solar eclipse lasting several weeks? These are my ...
25 views

### Surface Conditions

Planets like Saturn & Jupiter are called "gas giants"--does that mean that there is no surface to walk upon? Though some source of gravity is required to hold the gas in place, isn't it? Venus: we ...
57 views

### If Mercury and Venus where to collide would it make a habitable planet? [closed]

I have been wondering for a while now about a scenario of where if you combined Venus & Mercury would it be habitable if located in the goldy locks zone? I have found in my little research that ...
30 views

### If I point a camera at a “+x” visual magnitude object, how to estimate how many e- (carriers) are produced per second?

In this answer I estimated that if a DSLR (digital SLR) camera with an aperture of 40 mm were pointed at a satellite in geostationary orbit with a visual brightness of about +11 magnitude, it would ...
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### Geographical Substellar position calculation from RA/DEC

I was trying to help my son with a project and thought it shouldn't be hard but turned out I'm not as smart as I thought I was. His project is about celestial navigation. The first step is, given the ...
85 views

### What’s the closest earth like planet we have discovered in our galaxy? [closed]

What’s the closest earth like planet or moon to earth we have discovered in our galaxy?
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### Is it possible for stars not to rotate?

I'm just curious about that the existence of non-rotating stars. Is it physically possible for a star not to rotate at all? Does magnetic braking eventually stop the stellar rotation?
62 views
+50

### Any information on the salt content of Mars' atmospheric dust?

Answers to and comments on How to drink water on Mars? suggest that one would not want to drink melted water ice obtained from exposed surface deposits near the poles because it may contain various ...
381 views

### Would drinking melted ice water from Mars taste like sparkling water?

Does water on Mars form from the atmosphere as ice free from salt? Does water desalinize through the evaporation and transpiration? When the fresh top ice is placed in a container then pressurized to ...
135 views

### 3 years later, how strong is the evidence for planet 9?

I came across post in quora where somebody said that "most astronomers no longer think Planet 9 exists" and being somewhat shocked by that, I did a google search and found a fairly recent article that ...
36 views

### How to estimate uncertainty of measurements of equivalent widths?

I'm measuring equivalent widths of absorption lines using a spectrum of a star. I make two or three measurements of each line by making reasonable gaussian fits of the line with IRAF's splot tool. ...
51 views

### Will the shape of the constellations change if we observe from another planet, say Mars? [duplicate]

Constellations are dominant features of night sky. But these are basically group of stars that forms particular shapes when viewed from Earth. How much the shape of a constellation will change if we ...
65 views

### Could some bacteria theoretically evolve to survive in space?

There is no edge to the atmosphere, and therefor I expect there would be a gradual reduction of concentrations of bacteria as we ascend into space. Logically anaerobic bacteria should be able to ...
71 views

### Time Dilation and Particle Decay

I am teaching myself astronomy and I'm working on a basic problem regarding time dilation around black holes. The question is basically this: if a neutron were ejected from a nucleus at a distance of ...
76 views

### If the whole observable Universe is as big as planet Earth, how big would Earth be?

If the whole observable Universe is as big as planet Earth, how big would Earth be?
69 views

### Is Naboo's core possible in real life?

In Star Wars, the planet Naboo has a plasma core, instead of a molten one. Can a planet really have a plasma core?
83 views

### If the Milky Way galaxy is as big as planet earth, how big is Earth?

If the Milky Way galaxy is as big as planet earth, how big is Earth?
59 views

### Will Earth at some point stop rotating anti-clockwise, stay still, and then rotate clockwise? [duplicate]

Will Earth at some point stop rotating anti-clockwise, stay still, and then rotate clockwise?
35 views

### Under what situations can an aperture mask improve the resolution of a small/medium amateur telescope? Is this demonstrable mathematically?

@antlersoft's answer describes some of the challenges to seeing any details in the small disk of Mars in small amateur telescopes. In the case of reflecting telescopes, it mentions the use of either ...
1k views

### What is the “lost light” in this unusual Hubble Deep Sky image?

The Daily Galaxy article “The Lost Hubble” –New! Deepest Image of the Universe Ever Taken says: To produce the image a group of researchers from the Instituto de Astrofísica de Canarias (IAC) led ...
978 views

### How can gravitational lensing makes a quasar appear brighter?

How can gravitational lensing makes a quasar brighter than it would in the absence of a foreground galaxy?
96 views

### How did Johannes Hevelius' long telescope work? Why all the round holes?

The drawing below, found in Wikimedia and at lib.harvard.edu is of a very long tubed aerial telescope. I believe it is taken from his 1673 work Machinae coelestis. I've always wondered about the ...
41 views

### How long does it take a star to transition from main sequence to red giant?

I have read that it takes billions of years for stars of approximately the size of the Sun to get through the main sequence, after which it will enter the red giant phase. When that happens, how long ...
35 views

### Cases of gravitational lensing resulting in a recognizable image of an extended object?

There are several different classifications of gravitational lensing phenomenon. Here I am asking for any examples of strong lensing where the lensed image of an extended object is magnified and ...
81 views

### Why is the difference from a perfect sphere the same for the Earth and the Moon?

Wikipedia gives the following physical dimensions for the Moon: Physical characteristics ...
45 views

### Does astronomical observing “count” as remote sensing?

I have long considered astronomical observing as a form of remote sensing, though quite different than typical remote sensing in that many objects observed are not resolved. I am wondering, though, ...
48 views

### Circumpolar Equation Derivation

Edit: Geometric answer from Math.stackexchange I am trying to understand where the circumpolar equation comes from. $\delta \geq \frac{\pi}{2} - l$ I can understand that the sort of "rotation" of ...
57 views

### Do we know if there are asteroids leading or following Earth in Earth's orbit around the Sun?

A search of the Internet is so clouded with discussions about the asteroid belt or asteroids orbiting the planet Earth that I couldn't see an answer to my question. Do we know if there are asteroids ...
20 views

### Can Jupiter's nightside be classified as spectral type Y?

As far as I am aware, the latest spectral types that have been assigned are around Y2, for objects like WISE 0855-0714 that have temperatures around 250 K or so. I've also seen several directly-imaged ...
86 views

### What is the difference between the way light travels in a gravitational field and the way it travels through an expanding universe?

A photon is travelling through space. As it travels, the space through which it travels is expanding Does this describe A - a photon travelling from a distant galaxy to earth B - a photon travelling ...
23 views

### Combining lenses to make a telescope

Hi I have two Galileo 700mm x 60mm Astro/Terrestrial Refractor Telescopes. Can I take the lenses out and make one powerful telescope?
74 views

### How to Calculate Planetary Equilibrium Temperature in Binary systems

I'm working on a program that generates the basics stats of a terrestrial planets in binary star systems. I'm not the best at this kind of math, so I'm having trouble calculating the planetary ...
57 views

### Do Mercury and Venus exhibit retrograde motion?

This is more a terminology question, since Mercury and Venus certainly "move backwards" in the sky. The question is whether we call this retrograde motion. I'm referring to apparent retrograde motion ...
49 views

### Hubble Space Telescope (HST) observing modes

I have been reading some literature on using the HST to take spectra of exoplanet atmospheres when exoplanets transit in front of their stars. The literature mention two modes of observations, '...
72 views

### Earth Orbit Simulator [closed]

I'm trying to simulate Earth's orbit using 2nd Newton's Law and cartesian coordinates. The program seems ok, but when plotting graph, it's a parabola. I know the shape of orbit changes according ...
15 views

### How to zoom out in splot

I'm using IRAF's splot command to view spectra from stars. I can zoom into a segment by pressing a key on its right and left edges. I can also use z key to zoom in ...
50 views

### Star rising times in a different place given the latitude and time of one place

I dont know astronomy, but I am preparing for the second stage of IJSO, and here in India they do add some questions like these ones. ...
88 views

### I need help getting mars to look like a circle

I am having a lot of trouble getting a sharp image in my telescope. It is a skywatcher with a focal length of 1200mm and a diameter of 254mm. I have a laser colimater that I got for Christmas, so I ...
173 views

### When is Earth closest to the Sun?

When is Earth closest to the Sun? Well, you say, perihelion of course. But perihelion is when the Earth-Moon barycentre is closest to the Sun. Not Earth itself. The barycentre is on average 4,671 ...
137 views

### How fast will the sun grow when it becomes a red giant?

We all know that our sun will become a red giant in a couple of billion years? But how fast will the process be when it starts? Would it be theoretically possible (disregarding the deadly effects of ...
39 views

### Meteor shower shooting stars

Shooting stars are actually meteors falling down on the surface of earth. How come some of them appear shooting up and not down?

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