# All Questions

162 views

### Will the Sun rotate slower in red giant form?

When the Sun runs out of hydrogen to fuse it will grow bigger in size and my question is does it rotate more slowly, like a spinning ice skater extending their arms to reduce angular velocity? What ...
303 views

### Why are radio telescopes shaped so differently than optical telescopes?

Why are radio telescopes typically only a dish with a receiver above it, while optical telescopes have a primary, plus secondary and sometimes even a tertiary mirror? In other words, why do radio ...
377 views

### How long until the Earth and Moon become a binary planet?

With the rate at which the moon is further receding into a higher orbit, how long until the barycentre between us and the moon leaves the earth, and going by the IAUs 2006 definition update, we become ...
86 views

### Are trojans in L5 more likely than in L4?

Mars has much more trojans in L5. Does it reflect a common pattern?
230 views

### How has the Earth's orbit changed over hundreds of millions or billion of years?

First, I know that modeling orbital mechanics of 8 planets is hard, but there are some theories out there, for example, Jupiter is thought to have moved in towards the sun then started moving away. ...
67 views

### Who invented the blink comparator?

The Wikipedia page for the blink comparator fails to mention who invented it. Many other pages extol the importance of the device, but we cannot find any mention of an inventor. Wikipedia does ...
38 views

### How significant and accessible is modern Chinese astronomy?

Is China fully integrated in the international astronomical community, or does military secrecy and language problems and sanctions (ITAR) or something else stand in the way? Does China have valuable ...
50 views

### Suns Orbital speed and escape velocity question

This is a homework question and I don't want an answer but just want to understand what its asking for. We are given that a star with a mass of x solar masses in ...
35 views

### Semimajor axis variations in co-orbital moons

I've been playing with simulations of co-orbital bodies similar to Saturn's moons Janus & Epimetheus- horseshoe orbits where the two bodies are of comparable mass- and I'm seeing some very odd ...
74 views

### Why is $g$ tied to the oscillator strength $f$ in $\log{gf}_{\odot}$

The $\log{gf}$ value of an element in a star, where $f$ is the oscillator strength, or probability of transition in an atom, is a scientifically pursued quantity with relation to the model atmosphere ...
399 views

### How small would you have to crush an object for it to become a black hole?

I was wondering how much you had to crush an object for it to become a black hole. Recently I learned that anything could become a black hole (even you) if it were crushed down small enough, for ...
150 views

### What will the last days of Earth be like?

The sun is a main-sequence star; as I understand it the sun will expand into a red giant in a few billion years. I have heard conflicting reports of what this entails - some sources I found say the ...
444 views

### Are stars NML Cygni, UY Scuti, VY Canis Majoris and VV Cephei near the ends of their lives?

Are the four stars mentioned in the title stars that are going to go supernova, or are they stars that are in mid-life, like our Sun, but just happen to be so much larger than our Sun?
59 views

### Could martian meteorites come from Olympus Mons?

Could Olympus Mons have thrown ejecta out of Mars' orbit when it was active? Does it fit with the composition and dating of meteorites with martian origin?
81 views

### How to tell a crater is old or not?

Based on Wikipedia, we can estimate the age of a planet's surface. How to tell a particular crater is newly formed or not? It may have sharp edge. Different astronomical objects may have different ...
154 views

### about H$_\alpha$ and H$_\beta$ lines in astronomical objects' spectra

Generally there may be some line ratio between the two lines. If H$\alpha$ is strong, it is quite possible we can see H$_\beta$ too. Is it possible we can see H$_\beta$, but can not see H$_\alpha$? ...
129 views

### Where to get Polaris Right ascension value from

To calculate for example the polaris hour angle I use this formula to calculate polaris hour angle. τ = θ - α τ= hour angle θ= sideral time α= polaris RA (~ 2h32m) But where does the α=2h32m come ...
78 views

### Could the James Webb Space Telescope detect biosignals on exoplanets?

The James Webb Space Telescope (JWST) which is slated to launch in 2018 will bring us a better view of exoplanets, but will it be sufficient to detect signs of life on at least some of those worlds? ...
121 views

### How to run MOOG on OS X Yosemite

By what process can a user running the latest version of OS X Yosemite execute MOOG with \$MOOG in bash? Due to the removal of 32bit libraries in OS X 10.7+, the ...
167 views

### What is the axial tilt of a planet measured relative to?

I am very much a beginner on the astronomy front but I understand about planets having different axial tilts, hence why Venus turns the opposite direction from the Earth and Uranus turns sideways. ...
63 views

### Why doesn't the Moonrise appear red when viewed from orbit?

After searching through many videos, I finally found one that shows, from the perspective of low earth orbit, the Moon transiting the horizon. It is actually a Moonset, but it shouldn't make a ...
86 views

### Why was Pluto's resonance not discovered until 1965?

Over here, I was shocked to learn: The Neptune–Pluto system lies in a 3:2 orbital resonance. C.J. Cohen and E.C. Hubbard at the Naval Surface Warfare Center Dahlgren Division discovered this in ...
112 views

### How clearly would I be able to see a galaxy with the naked eye if viewed from a “close” distance?

In images of other galaxies they look very bright and vivid against the blackness of space (example). If I was located a few tens of thousands of lightyears away from a galaxy, would I see something ...
148 views

### Do NEA (Near Earth Asteroids) have minable water ice?

Water is very useful for rocket fuel and life support in space. But does water, in abundance and form which conceivably could be usefully mined this century, really exist in NEA's? Or do we have to go ...
34 views

### Why didn't we have inflation when the theory of everything and GUTS broke symmetry? [closed]

Inflation seems to have occurred when the symmetry breaking of the electroweak occurred. But do we know of any reason why we did not have inflation when gravity separated from the other forces or ...
121 views

### Stability of solar system

My question is simple: Is the Solar system stable? You can see this Wikipedia page. Edit: Sorry, because i think my question is more about mathematics and classical mechanics of planets in ...
88 views

### What is the air pressure in the heliosphere (Sun's atmosphere)?

Specifically, I am wondering what the pressure is at a distance of around 1 AU. Does it it decrease quadratically with distance?
267 views

### Does the Sun move? [duplicate]

I'm curious; does the Sun actually move? The concept behind the question is that if you wear a shirt and you move, does the shirt actually move? The Solar System orbits around the Milky Way, but does ...
57 views

### what is the time mentioned after date (1962-07-03+02:00) the +02:00? [closed]

i was retrieving a some personalities birthday date through computer programming when i retrieve a person's birthday the result was ...
313 views

### What causes horizontal and vertical lines coming out of pictures of stars?

What causes the horizontal and vertical lines coming out of pictures of stars, instead of them simply appearing as circles? For example, this picture from Wikipedia: .
118 views

### Accidental or deliberate? [duplicate]

We know that the visual size of the Sun and Moon from the Earth in our lifetime (!) is nearly equivalent. Now my question: Is this event is random? Or have a scientific reason? For example, maybe ...
66 views

### Eclipse on the moon

What kinds of eclipse is seen by the person on the moon, when there is: Solar eclipse on the earth, and Lunar eclipse on the earth?
114 views

### How much larger would a star have to be to cause thermonuclear reactions if it was made out of mostly rock like Earth, instead of gases?

I assume it would have to be considerably larger since rock isn't as flammable as gases are? But it's also more dense to begin with.. Do we know of any suns that are made like this? Is it even ...
561 views

### How to calculate conjunctions of 2 planets

So, the recent conjunction of Jupiter and Venus seems to have spawned lots of excitement over this "rare" event. But what I can't figure out, is exactly how rare it is. And I've seen such conflicting ...
40 views

### Are mass extinction events more likely during meteor showers / passing through comet debris?

Meteor showers happen when Earth passes through the debris left by a comet in its orbit. Meteors are generally tiny, like snow flings or pebbles and don't make it to the ground as meteorites. But ...
272 views

### How can Halley's Comet be predictable?

How can we know that Halley's Comet is going to come again every 76 years? I understand that the comet has an orbit around the sun but how can scientists know that it won't be thrown off course for ...
284 views

### What is the brightest star (by absolute magnitude) that we can see by naked eye?

Is it Rho Cassiopeiae or Mu Sagittarii? I see in the Stellarium 0.13.0 that Mu Sagittarii has absolute magnitude -11.43!!
73 views

### What is the next planned mission that can discover life on another planet? [closed]

I've heard that we have a great shot at finding life on Mars if we just drill deep enough down to the surface to the water and detect if its sterile or not. Are there planned missions to do this? If ...
105 views

### How to find Exomoons?

How would we be able to detect Exomoons? We detect exoplanets by seeing if the light gets faint from a star, but could we really use the same method for determining if there is an exomoon around that ...
120 views

### Stellar mass database

I need a stellar mass database that also has the distance of the star/system from the sun. Can anybody tell me the name of such of database and where I can find it. I need to do a project on this. ...
167 views

### Does a week represent something in astronomy? [duplicate]

I know that a day represent the time for the earth to make a full rotation around its own axis and a year is the time for the earth to make a full rotation around the sun. But does a week represent ...
61 views

### How far away would a supernucleus comet be visible?

If an instrument like LSST quickly spots something as soon as it reaches magnitude 24½, how far away would a 60km first-time visitor from the Oort cloud be when it is spotted? I'm thinking that a ...
178 views

### Is the diameter of the observable universe a relative quantity?

The diameter of my observable universe is 90 billion ly measured in proper distance. But isn't lenght a relative quantity in the theory of Relativity? Could an observer moving at a different velocity ...
2k views

### When will the next summer solstice and a full moon coincide? What day?

What day will the summer solstice and full moon coincide? As far as I know the next time will be in 2016. I would like to know what day.
101 views

### What is the projection of Earth's axis on the sphere with the Sun in center (see explanation)

Seems like it is the most convenient SE community for this question.. Imagine the sphere, witch center is the Sun and radius is, say, ~1.5 distance from Sun to earth (in arbitrary time, precise ...
290 views

### How to calculate the limiting magnitude of Hubble?

I've found various sources on the web stating that the limiting apparent magnitude of the Hubble Space Telescope is about 31 or 31.5. Wikipedia lists that here and it has a cite to a pdf about it. ...
97 views

### Which is the shape of the sky?

I'm a software developer and I'm developing a planetarium and the first thing that I don't know is: What is the shape of the sky? First, I though that it is a semi-sphere, but searching on Internet I ...
55 views

### material exchange between a planet and its host

Of the exo-planets found so far, there is one that can exchange material much with its host? How to prove that? Io may be a good example, but it is not a planet.