# All Questions

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### Why do we need radioactive material to test theory of relativity?

Why can't a stable element be used to test e= mc2?
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### How big should be a piece of neutron star to reach Earth's mass?

Imagine a neutron star could be broke into pieces. How big would be the piece matching Earth's mass?
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### What are these objects near Mirach

Night sky objects always interested me, nowadays Im trying to observe and photograph some of these objects. My phone is iPhone 6S, i used SkyGuide app to find positions, NightCap to photograph. Im ...
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### Bright star or flare near orion?

This morning at 6:12 am looking south from Georgetown, Texas, there was a brief very bright stationary object what appeared to be a star that once I saw it within the next few seconds quickly vanished....
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### Eccentricity and Inclination of a Star

I understand Planetary Eccentricity and Inclination. However when it applies to a star, does the centre or ecliptic plane refer to the Sun or the Galactic Centre? The star Sirius for example, 136....
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### Why does the sky look like it has three suns in this video? [on hold]

Check out @natalie9280’s Tweet: long story short, friday morning at around 6:40am i looked outside and i saw three suns. i checked to see if there was an eclipse and i could[n't] find anything. ...
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### lights move… why do we see it? [on hold]

For 4 years now, I have lived in a nice place away from others. But no one has confirmed the lights moving. Initially appeared to be a Star but moving, and then a different angle back and forth more ...
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### Site to see direction to the Voyager by entering time and coordinates of my position on the Earth?

Where is Voyager relative to me right now in realtime?
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According to Google, radial velocity is "the velocity of a star or other body along the line of sight of an observer". The radial velocity of Sirius according to Google is −5.50 km/s. If the ...
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### If the Higgs field only formed after the Big Bang, how was hydrogen formed?

These two statements seem to conflict, but since we're here they can't: Electrically charged particles cannot be massless. Hydrogen was created at the moment of the Big Bang. However, the Higgs ...
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### Measure an angle in the sky from a photo?

Let's say I have an picture of the sky or of an landscape and I want to measure an angle in the celestial sphere. Is there any software for that? In real life I would use the empirical hand gestures ...
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### Water Ice on Meteorites

I was reading an article by David O'Brien et al. where it stated "in meteorites only the water bound to the silicates can be found, all the water ice having been lost, whereas on asteroids water ...
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### Ratios of magnitudes instead of differences

The color index in the photometric system is defined by the differences in magnitudes between two wavelength filters, which gives the ratio of intensities. For example, to determine the B-V index, you'...
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### Why don't all perseid meteors follow the same trajectory?

Since these bits of debris crossing Earth's orbit have the same relative speed, why aren't they drawing parallel paths in the upper atmosphere? (consider one hour of observation to minimise Earth's ...
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### Which lens is right to see which planets with an Orion StarSeeker 150 mm?

I'm an amateur astronomy lover and I have an Orion StarSeeker IV 150 mm, together with a bunch of lenses, which are the following: 1x 23mm (32.6x) and 1x 10mm (75x) wide-field 60-degree eyepieces 1x ...
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### What are the procedures and protocols to use with Gauss'method and personal observations?

I would like to use the Gauss' method to determine the orbit of planets of solar system. I would like to calculate their orbits with personal observations. What is the methodology/procedure/protocol ...
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### Endogenous Theories For the Origin of Earth's Water (Dry/Wet Accretion?) [duplicate]

I have really two questions: what evidence is there in favour that the majority of Earth's water formed with the planet. what evidence is there that the majority of water did not form with the Earth. ...
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### Energy conservation in Barnes-Hut algorithm [on hold]

I wrote a code that follows the Barnes-Hut algorithm for gravitational dynamics. Everything looks pretty good, except that when I plot the total energy $$E_{tot}\equiv E_k+E_u=const$$ I get this ...
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### Can I take logarithms of magnitudes (which are already log)

I'm investigating the relationship between the magnitude of quasars in various wavelengths, and their redshift $z$. I've found that if I take the $log$-$mod$-transform ($L_{mag}$) of the magnitudes, ...
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### Orange light that rises quickly and moves of to the righ [duplicate]

I have recently noticed an orange "star" (or what I presume to be a star), rise above the hill line behind my home. It rises later than every other star and rises within a few hours while the other ...
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### Studies of isotropy from different ends of the visible universe?

Have there been studies to compare structures that are 26 billion light years distant (i.e. from one side of the observable universe to the other) to search for faint differences?
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### Would a nuclear explosion over one of the Earth’s magnetic poles momentarily disrupt/weaken the Earth’s magnetic field? [migrated]

If say the Tsar Bomba had been detonated directly over one of the Earth’s magnetic poles at ground level, would the nuclear electromagnetic pulse generated from that blast have had any momentary ...
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### Dataset containing list of known globular clusters

Does anybody know if there is an existing dataset that consists of all known star clusters, their name, and their apparent dimensions or similar? Is it possible to make a query to, or download all ...
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### We are in Green Lake, WI, 8/12/18, seeing bright orange “planet”/“star” almost due South, perhaps 20 degrees above horizon, what is it?

I have a “sky” app on my ipad and expected it to be Mars, but my app shows Mars just below horizon and closer to East. Oh, I should add that we saw this about 10:15 tonight. Hanging out watching ...
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### Which telescopes model is being shown to Albert Einstein in this file footage? What event might this be?

In the Economist video Why does time pass? there is some file footage of Albert Einstein attending some event where a model of a large telescope is on display, and being described to Prof. Einstein. ...
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### Are there simplified M-L, M-R, and lifetime equations for non main sequence stars?

To give some context - I am trying to create a simple program that outputs the stellar properties of a star when given its initial mass and current age. e.g. Input Initial Mass = 2e30kg Age = 4.6 ...
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### What is the maximum Clear Sky Light Pollution rating to see the 2018 Perseid Meteor Shower?

I'm talking about the Light Pollution ratings on this page: http://www.cleardarksky.com/csk/faq/2.html I live in an area which is a 7 on the Bortle Scale ("red" on clearsky.com), but within 2 hours ...
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### Why are gravitational perturbations stronger at larger semi-major axes?

Why are mechanisms such as the Kozai-Lidov effect more prominent at at large semi-major axes? If we had a binary system of a primary and secondary body, with the third perturber as the Sun. Why is it ...
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### I am beginner here.Could any one please suggest telescope on AliExpress [closed]

I am beginner and eager to buy telescope for viewing planets and deep sky objects. I have gone though several posts here and found that only magnification is not so important but along magnification ...
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### Magellanic Clouds

The Magellanic clouds do not seem to move much relative to the other background stars, which of course move a good deal. Is there some explanation for this or am I observing poorly?
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### How bright is Andromeda's center, in magnitudes per square arcminute or something similar?

I'd like to know how bright the Andromeda galaxy's core is as an extended object, not the total integrated brightness. Ideally a contour map or scan across the center might show brightness in ...
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### Why would the interplanetary medium atomic hydrogen Lyman‐α emission fall as 1/r rather than1/r^2?

The Live Science article NASA Spotted a Vast, Glowing 'Hydrogen Wall' at the Edge of Our Solar System links to Geophysical Research Letters The Lyman‐α Sky Background as Observed by New Horizons https:...
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### What would go into the design of a sky quality meter, used to measure night sky brightness?

@MCG's answer mentions several methods to classify night sky quality or brightness, and goes on to say: Additionally, you could always purchase a SQM (Sky quality meter) which is a small, portable ...
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### What is “class 4 light pollution” and could I estimate my own area's class visually?

This question currently asks I am living in the northern hemisphere in Greece and in class 4 area (light pollution scale).Is it possible to see the Andromeda galaxy with a naked eye? I'd never ...
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### Why would the Perseids meteor rate fall off after maximum faster than the increase before maximum?

Writing about the 2018 occurrence of the annual Perseids meteor shower, the EarthSky.org Astronomy Essentials article Start watching for Perseids now says: People tend to focus on the peak mornings ...
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### Why aren't neutron stars full of dark matter?

Dark matter interacts with the gravitational force right? Well, unlike black holes, neutron stars are actually visible, and they're an enormous gravitational sink, so dark matter should collect to ...
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### Has the Penrose process ever been linked to an observed phenomenon in some way?

This answer mentions the Penrose process as a potential mechanism that could change the axis of the orbital angular momentum of an accretion disk around a black hole away from the original axis of the ...
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### Orange light in sky

It is 1:15 am, 8/10/18 in Indiana. I looked out my kitchen window and saw an orange light to the north.. color of a street light but clearly out in space. Sitting about as high as a full moon at ...
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### How big does the moon have to be to have the Earth tidally locked to it

I would like a earth-moon system like Pluto-Charon (but with earth instead of Pluto) where both will be tidally locked to each other within something like a billion years. As the moon would probably ...
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### Why does D4000 affect stellar age?

From my understanding D4000 is a ratio between the 'flux densities between 4050 and 4250 Angstroms and that between 3750 and 3950 Angstrom', from Poggianti et al (1997). However I do not understand ...
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### The formation of new stars as depicted in Feynman's lectures

I've stumbled upon this curious passage addressing the formation of stars in Feynman's lectures on physics: Whether we have ever seen a star form or not is still debatable. Figure 7–12 shows the ...
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### Total angular momentum in system of binary brown dwarfs on wide orbit from primary star

I want to calculate the total angular momentum of a system in which two brown dwarfs are orbiting one another (P ~ 10 years), and this system is stably orbiting a third primary ZAMS star (P ~ $10^4$ ...
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### Things to be aware of when designing a custom equatorial fork mount

I'm still relatively new to amateur astronomy, and I would like to get into astrophotography. I've looked at different equatorial mounts, and I think I like the benefits of fork mounts. I'd like to ...
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### Lunar orbit distance

Can anyone calculate the distance the moon travels in a single year? I can calculate it as it is close to 2.4 million km, but I need adjustments as the earth is moving and so is the Sun. So, I need ...
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### What is the meaning of “bright unresolved sources”

In many articles talking about telescopes, they talk often of "bright, unresolved sources". "bright" usually mean that the magnitude should be less than a certain threshold, (or that the signal to ...
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### Is it possible to view the Andromeda galaxy with the naked eye in Greece?

I am living in the northern hemisphere in Greece and in class 4 area (light pollution scale). Is it possible to see the Andromeda galaxy with a naked eye?