# All Questions

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### Are we still going to have rainbows if Sun is replaced by another star?

Rainbow is a property of light splitting due to the water molecule present in the clouds and is related to the light emitted by our Sun. Our sun is a yellow star. Now if we replace sun by a blue giant ...
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### Formation of our Universe

So I got this information from a magazine , Scientific American issue Physics at the Limits. The theory is that our Universe came about, when in the "Bulk Universe", which is four dimensional, a four ...
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### Looking for an equation that describes how star (x,y,z) positions are affected by expanding universe

I understand that coordinates of stars are in RA,DEC. I am looking for a mathematical expression that describes how the positions of stars change due to the expanding universe.
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### What if Earth and Moon revolved around each other like Pluto and Charon?

What would be different for us if Earth and Moon revolved around each other like Pluto and Charon do?
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### In a binary star system, what relation determines the eccentricity of the three orbits (for $m_1$, $m_2$, and the reduced mass)?

In a binary star system, why does $$e_1 = e_2 = e$$ where $e_1$,$e_2$, and $e$ are the eccentricities of the three orbits of $m_1$,$m_2$, and the reduced mass, respectively.
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### Why don't the stars in a binary star system of equal masses always orbit their center of mass in a circular orbit?

If I have a binary object system of equal masses, why don't they always have the same circular orbit around their center of mass, like in the photo?
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### What types of meteorites can I use for making a wedding ring? [closed]

I want to buy some meteorite and put stones made from it into gold or platinum ring. Or maybe I can use some metal meteorite for making ring? What kinds of meteorites can I use? It must be strong, non ...
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### How many planets have we discovered that can support human life?

I have heard a lot of buzz about distant planets that could potentially be second homes for human existence, but what is that approximate number?
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### Two black holes photo interpretation

Please see this image: I wonder two things about these black holes. The first is, what are the oblong, smaller black hole-looking voids outside the perimeter of the major black holes? Also, why are ...
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### How to tell a pulsar is rotation-powered or accretion-powered?

We need to calculate P/Pdot? A pulsar may switch between theses two states. For a rotation powered pulsar, it can pulse and, the pulsed Lx can be much larger than the luminosity given by its ...
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### Quasars and Gamma Ray Bursts

Has there been any study to suggest that either quasars of gamma ray bursts are more detectable from further distances in the universe? I've read that quasars are the most powerful energy in the ...
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### Is there any real evidence to prove or disprove the existence of alien civilizations?

Is there any real proof that alien civilizations exist in outer space? What if someone were to say that Earth is the only inhabited planet in the whole universe? How would you respond? I need to ...
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### What's the relation between Einstein's Gravitational Theory and Dark Matter?

I was reading an elementary book on dark matter (in fact, a historical perspective) and there were mentioned how the scientific community react to the idea of dark matter proposed as a solution to ...
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### Betelgeuse and sun classification

In this video, between 4 and 6 minutes, the lecturer describes M type stars as being less massive, smaller, and redder than G type stars. He then gives Betelgeuse as an example of an M type star and ...
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### Oldest in the universe

When the big bang happened and all that exist today came into existence from singularity, how do you determine which part of the universe is the oldest? Its natural to think that looking back at the ...
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### The contents of potential “message” in the Wow! signal lost?

The Wow! signal is still an enigma. I understand the incredibly high signal strength it entails. This during some time-period because the sweep of the alignment (or rather the receiving station). ...
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### Can the centripetal force be inverted? [closed]

Using the centripetal force to create artificial gravity has been proposed for space exploration. From our perspective, the force is an outward force, pushing objects away. Could it be inverted to ...
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### How does one reference the Hubble constant?

I want to use the current value for the Hubble constant 73.8 km/s/Mpc in a paper. How do I reference this value?
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### When is it a good aproximation to consider a star to be an ideal gas?

I am currently taking a first course on stellar astrophysics, and I noticed that in some cases we use the ideal gas equation of state for stars, so we also use $\gamma =5/3$. Of course it can only be ...
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### Why would the Earth's solar analemma would be still a figue eight even if Earth's orbit was circular?

The Earth's solar analemma is a diagram showing the deviation of the Sun from its mean motion in the sky, as viewed from a fixed location on the Earth. ... For [a planet] with a circular orbit but ...
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### What is the illuminance of Tau Ceti?

As part of my physics project, I investigated the relationship between a light bulb's illuminance and the distance from the measuring device to it. Illuminance was measured in flux, and distance in ...
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### How do you estimate the error on the height/width of a Gaussian?

I'm trying to fit Gaussians to several lines in a spectrum that I have. Some of them overlap with one another, causing the fitting program that I'm using to not be able to give reasonable estimates ...
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### Why does Saturn have both moons and rings?

From my understanding, a ring can form around a planet when a moon gets too close to its Roche limit, and gets ripped appart by the planet's gravity pull. That makes sense to me, but I don't ...
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### What is an “arc” spectrum ?

I sometimes hear about astronomers using an arc spectrum to calibrate observations. For example a "He-Ar arc spectrum". What is an "arc" in this context? I assume it's nothing got to do with angles (...
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### Name for 1-e and 1+e terms?

In several equations of orbital elements (such as the determination of true anomaly from mean anomaly), the terms 1-e and 1+e appear. These are the ratios of the orbital periapsis and apoapsis to the ...
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### What is the composition of an asteroid in percentages?

I am developing a RPG game (or so I like to tell myself) within outer space. Within the game, players would be able to mine small asteroids and collect resources, in order to make money. I'm having ...
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### What does an Einstein-De Sitter universe look like?

I know an Einstein-De Sitter universe is a "flat" universe, i.e. with a K ("bendiness", sorry, don't really know what to call it in English) factor of 0, but does that entail anything as to its ...
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### Simulate an orbit with orbital elements

I want to simulate the orbits of the planets from our solar system. I want to use orbital elements to calculate the current position(xyz) at a time t. The simulation doesn't have to be too exact, but ...
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### Rings around a smaller, close-in planet?

Is it possible for a small, close-to-star planet to have a stable ring system--icy or otherwise? A smaller planet means the rings would have to be closer to the planet, which means the radial shear (...
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### Ambiguity in Earth's “Tilt”

It’s well-known that the axial tilt of the Earth (with respect to the ecliptic) is about 23.4 degrees. However, two angles is needed to specify the orientation of any rigid body, so it’s unclear to me ...
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### Why do certain massive stars leave no remnants?

Mass and metallicity are the two main determinants for a star's fate. This is simple enough. What's more complicated is how exactly these determine the star's fate. For example, you can see in this ...
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### Are we sure there are no planets inside Mercury's orbit?

Currently, most explorations about new planets are pointing to area outside Neptune's orbit, but how about inside Mercury orbit? Can we say for certain there are no planets inside Mercury's orbit?
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### Can a star orbit around multiple planets or a planet with massive moons?

Note: I'm not talking about a star orbiting around a single or lonely planet :) I know a star orbiting a planet is almost impossible because if a planet is more massive than a star, that "planet" ...
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### How many stars are in the Sculptor Dwarf Galaxy?

The Sculptor Dwarf Galaxy is a small satellite Galaxy of the Milky Way. There are many such satellites galaxies and I'm trying to compile basic data on them. However, I can't find an estimate for the ...
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### Stellarium script star of bethlehem

Does anyone out there have a script to replicate the star of Bethlehem. In this case meaning a conjunction of Venus and Jupiter near Regulus.
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### Can quantum entanglement cause nucleosynthesis to happen in stars?

Even if there isn't enough heat and energy in the star to cause nucleosynthesis, could atoms quantum entangle to create a new atomic nuclei? Or would it be quantum tunneling - if this is possible?
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### Can we simulate Earth's gravity in space?

Earth gravity is 9.8 $ms^{-2}$ Gravity on ISS(international space station) is 8.2 $ms^{-2}$ approx. As per this http://physics.stackexchange.com/questions/29929/gravity-on-the-international-space-...
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### Alignment of Semi-Major Axis of Orbits

So I'd like to ask whether the semi-major axis of planetary orbits are aligned? Logically, they shouldn't be, but many websites act as if they are. If they're not aligned, what's the angle between the ...
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### Are high-speed galactic collisions survivable?

This is a hypothetical question, but it really is meant as a vivid way of asking about the affects of high-speed galactic collisions. The November 27 APOD showed the Cheshire Cat galaxy group, and the ...
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### How (un)stable are the Lagrangian points 1, 2 and 3?

A couple questions, please: I know that the Lagrangian points 1, 2 and 3 are unstable and special Lissajous orbits plus some station-keeping are required to place a spacecraft around them. But I was ...
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### Software to convert RA and DEC into ALT and AZ

I have implemented the formulas to convert AR and Dec into altitude and Azimuth in C++ following the book Practical Astronomy with your Calculator or Spreadsheet 4th Edition. In the book there is an ...
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### What is the scale of things you can see with gravitational lensing?

I'm trying to understand the examples of gravity lensing (using the general relativity property of large masses to bend light like a lens). Most of the examples I see are of some galaxy (presumably ...
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### Can an SMBH recycle dark matter into energy?

I just had a conceptual question, hopefully it makes for some really interesting answers. I was wondering, as most galaxies have an SMBH at their centre (see Kormandy & Richstone 1995; Richstone ...
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### A black hole that doesn't take in matter?

According to List of Common Misconceptions by Wikipedia, under the heading of astronomy, this line can be found: A black hole can act like a "cosmic vacuum cleaner" and pull a substantial ...
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### Calculation of hour angle

I need to determine Right Ascension and Declination from Azimuth and Altitude, working in C#. The problem is that the formula for calculating hour angle, for some reason, doesn't work. Here's the code:...
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### A star a black hole and planets around them

Imagine we have a black hole and a star. There are very close to each other so black hole slowly consumes the star. It is possible to have planets in this system, and for them not to be consumed by ...
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### Would a satellite in geosynchronous orbit between the earth and moon track across the sky together?

On Nov. 25 at 2:30a.m. from southern California while viewing the moon with a 70mm D x 400mm F telescope a point of light was seen at about the 7 o'clock position below the moon. As viewed the point ...
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### What was the largest telescope ever fitted with an eyepiece

Serious modern telescopes use CCDs to capture the results. This makes it convenient to process or display the results halfway around the world. However, there is something visceral about looking ...