# All Questions

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### Planet-timer “device” from 1970s or 1980s possibly by Edmund Scientific

Many years ago (early 80s or late 70s), I bought a cardboard "device" which I think was called "Planet Timer" and I think was sold by Edmund Scientific. Does anyone have any information on this ...
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### How gravity works in a black hole? [closed]

In astronomy class, we have to state how gravity work in the black hole? I know for one fact is that black hole is strong enough to stretch you thin enough like a noodle. Any ideas?
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In radio/microwave observations, I understand the beamsize is the response of the telescope to a point source - effectively, the telescope's resolution. Now, the Planck satellite (par exemple) ...
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### How to disentangle a very distant star's relative velocity vs. redshift distance

We measure a star's relative velocity towards or away from us via its Doppler-shifted spectrum. This is also how we measure the distance of very distant stars: measuring the shifts in the spectrum ...
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### How to determine atomic number density of an element in a star based on equivalent width measurements

Given an equivalent width measurement $W$ of a spectral line of element $X$ and the effective temperature $T_{eff}$ of a star, how can you determine the atomic number density of $X$ in that star? ...
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### Best approximation for Sun's trajectory around galactic center?

What is the current best approximation for the path the Sun takes around the center of the Milky Way? I have found some information on the approximate position of the Milky Way's center, the speed of ...
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### Do orbital resonances always form naturally?

For example, if I throw two planets to orbit a star at random direction, would they form an orbital resonance?
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### Is it possible to see a moonrise or moonset twice in a day?

I've been wondering this for quite some time. Due to the variations in tilt from the earth we know that moonrise/moonset times vary. Is it possible that in any location on the earth one might see ...
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### Is Jupiter just a super earth with hydrogen atmosphere?

Often I see books which state that Jupiter has a rocky core, if it is true, does it originate from super earth with excessive collection of hydrogen?
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### Do the terrestrial planets form later than gas giants in our solar system?

Sorry I forgot where this statements come from, but I also remember the reason behind it is due to young Jupiter moves inwards and destroys the original super earth in inner solar system, and the ...
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### Why does the moon appear on cloudy night sky?

Now, I was looking the sky when I saw the Moon showing up in a sky completely cloudy, like this: But a little different. The clouds were doing an eye shape. What does explain that phenomenon? ...
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### What is the minimum distance from city that allow to see Milky Way plane? [closed]

The light pollution fades the starlight coming from the Sky and this dont let people to see the Milky Way disc. Is there any study about this?
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### How does one find the extinction coefficient of a particular galaxy?

I am doing photometry on a number of objects in a number of different galaxies. I need the extinction coefficients for these galaxies for various filters passes. Is there some database that displays ...
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### How did Mars come to have a 24 hour 39 minute day?

Mercury rotates three times for every two revolutions around the Sun, apparently due to a gravitational resonance with the Sun.Venus takes about 225 days to rotate, and rotates in the opposite ...
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### What are the arguments against the Feng and Gallo thin disk explanation of galactic rotation curves?

The well-known galaxy rotation problem is described here. Basically (as one moves outward from the galactic centre, $R$ increasing) the observed pattern of variation in orbital speed $V$ is very ...
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### nasaworking on a way to travel faster than speed of light [closed]

even if they did how will time pass in that ship. Also that ship would require a infinite amount of energy to fight the drag.but what would provide the drag since in space there is nothing to resist?
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### 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. ...
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### What is in the brightest area of the night sky?

When I look up in the night sky, I assume the brightest area, commonly known as "The Milky Way", is the Galactic Center of our home galaxy. But then I stumbled upon this illustration, which seems ...
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### How long does it take Dawn to orbit Ceres?

I haven't been able to find the orbit time of Dawn around Ceres. Do you know how long it takes?
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### Strength of gravity during the big bang?

I was watching a documentary on the big bang, one of the astronomers said that initially the four fundamental forces were combined as one, they then emerged to become: The strong and weak nuclear ...
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### White dwarf's impact on orbiting bodies

Recently the Kepler telescope in its study of white dwarfs detected the first planetary object transiting a white dwarf in the data from the K2 mission. It was consistent with earlier theories' ...
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### How do we know that light is redshifted/blueshifted and not the original light of a star/galaxy? [duplicate]

If a star/galaxy is moving towards us, then its light is blueshifted, and if it is moving away from us, then its light is redshifted. How do we exactly know that the color we are seeing is not part of ...
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### Does more ocean on an Earth analog produce a different rotation period?

Would an exoplanet that has more ocean than Earth rotate at a different speed as a result of this? Would the amount of water impact the weight, gravitational pull, and/or tidal forces and cause a ...
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### What is meant by matter distribution?

Frustratingly, I find this could be a very simplistic question and may leave me feeling a little stupid for asking it. But I have to ask this. My lecturer keeps refering to "matter distributions" for ...
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### Is axial tilt critical for life?

According to this explanation at the Georgia State University website, Axis Tilt is Critical for Life . . . The Earth's spin axis is tilted 23.5° with respect to the ecliptic, giving ...
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### Can you see pleiades and sirius at the same time on the sky?

I am would like to know if you can see pleiades and sirius on the sky at the same time from Greece? What time of the year would that be? And I would be very greatful if someone knows some interactive ...
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### What is the temperature on surface of Pluto facing Sun?

According to wiki page, the mean temperature of Pluto is 44 degree K (-229 degree C). However, given that Pluto is tilted greatly and there is daylight for long periods on part of Pluto facing the Sun ...
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### classification of the Kozai mechanism

As Wikipedia says, In celestial mechanics, the Kozai mechanism, or the Lidov–Kozai mechanism, is a perturbation of the orbit of a satellite by the gravity of another body orbiting farther out, ...
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### Which stars have been named after astronomers?

Most apparent stars have ancient names. But some of the newer (since 200 or so years) discoveries have been given the name of some prominent astronomer. Kapteyn's star is one example, and there are ...
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### Could an asteroid knock the moon out of its orbit?

As describe in this CNN article, an asteroid is going to pass near the Earth on Halloween. The article says that As it misses Earth by about 300,000 miles (slightly farther away than the moon), ...
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### Does the Sun turn around a big star?

The moon turns around the Earth. The Earth turns around the Sun. Does the Sun turn around a big star? If so, does this big star turn around a very big star? ... etc ... What are all the intermediate ...
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### When will all eight planets in our solar system align?

Ignoring expansion of the universe, entropy, decaying orbits, and interference from any bodies colliding with or otherwise interfering with their orbits, will the eight planets known planets in our ...
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### Theoretically, what is the biggest optical telescope that may exist?

Recently, I read yet another news about E-ELT. It will have 39.3-metre-diameter segmented primary mirror. And I was interested in the next question: Theoretically, what size of the primary mirror ...
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### When the sun explodes, will some of the planets in the Solar System survive and become rogue planets?

Say if a large enough star, that has a number of planets, were to explode in a supernova: Would any of the planets survive? Would they become rogue planets?
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### What would night sky look like if Earth was made of antimatter

Let's assume that Earth in its current state is suddenly replaced with the Earth completely identical, but made entirely of antimatter. Ignoring meteorites and asteroids which would cause mass ...
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### How astronomers distinguishes between natural and artificial signals coming from outer space?

How astronomers really distinguishes between the natural and artificial signals? From time to time astronomers detects many signals from outer space and SETI is always trying to find signals that ...
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### Is a supernova's core temperature absolute zero just before collapse?

I thought a supernova's core temperature was absolute zero just before it collapsed, as it has run out of all nuclear and thermal energy, but I haven't been able to confirm this online anywhere and I ...
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### Uncertainty in the FWHM (IRAF)

I measured the FWHM (Full Width at Half Maximum) of several emission lines using SPLOT in IRAF, and now need to calculate the uncertainty. How can I do that?
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### Why can't this be the simple (and obvious) explanation for the dimming of KIC 8462852?

Couldn't it be just a relatively large object, anywhere in the interstellar space between the star and Earth? I mean, look out the window at a far away car or a tree, then stretch out your hand and ...
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### Is there a database for stars? [duplicate]

I'm interested, is there any database of stars which I could browse on the internet? It would be good, because I could read their parameters, features and maybe find a picture about it. Thanks!
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### What is space temperature around Earth?

What is the equilibrium temperature that a black body will reach at the Earth's distance from Sun?
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### Tidal lock of earth and moon

As the Moon is tidally locked to Earth, that means, from Earth we can only ever see one side of the moon. Can we see all the sides of the Earth, from the moon?
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### Acceleration in Galaxies Collision

In the far future the Milky Way and Andromeda will collide. As far I know direct collision between large dense objects (black holes, stars, planets, etc.) is unlikely due to the relative "low density" ...
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### Can a probe orbit Pluto given Charon's gravity?

Is it possible for a man-made probe to orbit Pluto given its closeness to Charon? The gravitational field interaction of Pluto and Charon is likely to make simple orbit structure difficult for a ...
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### Why nuclear fusion is a controlled process in stars?

Nuclear fusion is the main way for stars to generate energy. But we know that nuclear fission and fusion are not controlled, then it causes chain reaction and sudden explosion. But why in the case of ...
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### What would happen if a rogue planet hit one of the planets in our Solar System?

As their are millions of rogue planets in the Milky Way, what would happen if one hit a planet in the Solar System. For example, if the rogue planet hit Pluto, would Pluto fall in to the Sun due to ...
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### What were the 2 satellites I saw this morning?

This morning at 6:03am Israel time (3:03 UTC) I saw, simultaneously, what appeared to be 2 satellites streaking across the sky directly overhead. If I remember correctly, they were both coming from NW ...
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### Is the time lapse considered when estimating the age of the universe?

We say that our universe is 13.7 billion years ago. During the big bang, it doubled at least 90 times in trillionth of a second (as given here), and other topological statements. The question is ...