# All Questions

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### Could an ejected “extra ice-giant” still be lurking in distant solar orbit?

BACKGROUND Hot Jupiters are thought to have migrated inwards, implying that another giant planet has been ejected in order to conserve the orbital momentum of those planetary systems. The number of ...
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### How can they tell no asteriods will hit earth in the next hundreds years?

It has come to my mind this interrogation : How can they tell no asteroids (big enough to create damage) will hit earth in the next hundreds years? Because, so far, we were unable to get a clear ...
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### Calculate time when star is above altitude 30°

To find the best observation time for an object, I'd like to calculate the time when it is 30° or more above the horizon. Local Sideral Time would be sufficient. To include that in my program, I need ...
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### How many nested stable (1 Mio years) orbits are theoretically possible?

If we look at our solar system we have the sun which has planet orbits and planets have moon orbits. If we look at the possible size difference from hypergiants to small asteroids why shouldn't it be ...
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### Problem with Dobsonian reflector telescope

I'm not sure whether I should ask this question here but I'll give it a shot. I have a XT8 Dobsonian Reflector telescope and it works fine. But recently when I use the focuser to focus the image when ...
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### Where does the solar system end?

This is a question I've heard many times in the past, and a quick search of the site says it hasn't been asked here, so I figured I might as well ask (and answer) it. I know that it is rare for ...
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### Official Definition of Satellite?

So I had an argument with a friend, which was about whether the Moon is a planet or a satellite. IAU 2006 Resolution B5 gives definitions on what it is to be a planet, but there is a vagueness, as I ...
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### Speed of light through the ISM and Wavelength

Articles written about fast radio bursts describe the signal's short-wavelength components arriving before its longer-wavelength components, suggesting energy-dependent time delays in the interstellar ...
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### What is the bluest narrow band filter mounted on ground based telescopes?

If we want to check a QSO's lyman alpha narrow band image, could a ground based telescope do that? I mean under the circumstance that its lyman alpha shifts to 3300A.
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Regarding solar system dynamics, i.e. planets in stellar systems and moons in planetary systems, this is often mentioned in the literature, but it is difficult to find a good analysis/explanation of ...
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### Can stellar black holes cancel each other?

Hypothetical question: when a pair of identical stellar black holes are very close to one another wouldn't the side facing each other experience lower gravitational force? How is this logic un/sound?
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### Planets and moons positions in cartesian coordinates?

Is there freely available and reliable source, where one can find positions of planets and moons of the Solar system at given time in cartesian coordinates? (I am writing a simple gravity simulator ...
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### Historical astronomical lunar tables

I hope this is the right place to ask this question, and I apologise if not. I've come across a date written in an old book, but it is written using what seems to be a lunar/zodiac system. Below is a ...
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### Is the Universe really expanding at an increasing rate?

Here's what I just read from Wikipedia's page on the Hubble Space Telescope: While Hubble helped to refine estimates of the age of the universe, it also cast doubt on theories about its future. ...
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### If Venus and Mars changed places, would we then have 3 habitable planets?

This is the supposition: Venus is too hot, Mars is too cold. If they switched places then Solar energy would change to make both more Earth like. We might as well have had three instead of just one ...
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### Which kind of properties can we get for cosmic ray particles hitting on an optical ccd?

It is very common that we meet cosmic ray particles in optical images recorded by CCDs. You can see the "snowflakes" in the hubble images below: Generally we should remove them in order to get ...
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### How to calculate the moon phase

I need a way of to calculate the moon phase. Do you know resources for research the theory from behind this? I basically have searched in Google, but the results were not very satisfactory. Exists a ...
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### 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. ...
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### Energy required for light speed [closed]

It is said that in order for us to travel at the speed of light, there has to be an infinite amount of energy. Light is made up of photons but photons themselves do not have an infinite amount of ...