The science dealing with objects and phenomena located beyond Earth. In particular, this applies to observations and data. At its core, astronomy is the physically informed cataloging and classifying of the contents of the universe in order to better understand what is out there.

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How to Find how far away could binary system be?

Human eye resolution is about one arcminute. Two stars in a binary system are separated by 10 AU. How far away can they be such that your eye could still distinguish them as two separate stars rather ...
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170 views

Which BICEP2 r value should be compared to Planck's r<0.11?

The BICEP2 paper reports a tensor/scalar ratio $r = 0.20_{-0.05}^{+0.07}$, but then says: Subtracting the various dust models and re-deriving the r constraint still results in high significance of ...
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8 views

Calculating distance to a binary as well as star pair in cluster, based on reference star data of related spectral class

The problem at hand consists of calculating the absolute magnitude $M_V$ for a B0V type star, then the distance to a binary system with one star A1V and one B0V type star, and finally a star pair ...
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146 views

Why is there a line in the middle of the Planck full sky map?

Why there is a straight line (or perhaps a flat surface) in the middle of the Planck full sky map? and zoom (it makes it seem that the big bang was a collision between two unknown surfaces)
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33 views

Compute the colour in the AB photometric system [closed]

I have a question for homework and don't get it at all: Consider two filters as shown in the figure below. Compute the colour S1 - S2 in the AB system for a star with flux: where is a constant ...
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28 views

The luminosity function

I'm trying to figure this out for the case... Supposedly the average luminosity will be equal to but how :S I know is the number density of galaxies per unit volume and luminosity but that ...
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1answer
46 views

Import of Celestial Effects on Satellite Radio Interference

Some internet (among other) infrastructure comprises satellites, which beam communications in radio frequencies. These satellites, to ground observers, appear as very small solid angles in the sky. ...
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3answers
184 views

Is there any dynamical reason for the winter solstice to happen close to the perihelion?

When the winter solstice arrives, the angular momentum of the Earth, its orbital angular momentum and its radius vector with the orbital focus in the Sun are in the same plane. This happens quite ...
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14 views

Advancement of perihelion, data [migrated]

I was looking for accurate and up-to-date data regarding the advancement of the perihelion of the planets in the Solar System, the only ones I've found so far are at least 90 years old bout I really ...
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3answers
71 views

Why is the Moon not redder at moonrise/moonset?

Okay we all know about Raleigh Scattering, which makes the sky blue. And by the same token, sunsets appear red because sunlight traveling through more atmosphere will "lose more blueness" as it's ...
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203 views

What would we see if we looked at our Solar system from 2,000 light years away with our current technology?

Assuming the tables were turned and we would live in a system like Kepler-422/423/424, some 2,000 ly away. If we'd look at the Solar system with a telescope like Kepler and using techniques like ...
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6answers
404 views

Is antumbra part of shadow darker than penumbra part of shadow?

I'm exploring different types of shadows casted by objects. I want to know if antumbra part of a shadow is darker than penumbra part. I've found two misleading pictures on Wikipedia: First: Second: ...
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1answer
182 views

Analyse astronomical data

Recently I was told of a job offer to analyse astronomical data. The job offer states that they want somebody with knowledge of astronomical data analysis software and it will be a plus somebody who ...
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1answer
57 views

How do we estimate the amount of $10^{23}$ stars?

Now, I read somewhere, that there are $10^{23}$ stars in the universe. How did scientists estimate this?
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1answer
56 views

Do septuple (7), octuple (8) or nonuple (9) star system exist?

The highest I found so far is Castor, a sextuple star system. And there doesn't seem to be any other sextuple star system within at least 100 light-years...
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1answer
29 views

Binary Mass Function Plot

Suppose that we have a circular eclipsing binary system with orbital period of $P = 2 \text{days}$, and with one star with a radial velocity of $v_{1r} = 100 km/s$. The other star is to dim for its ...
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1answer
69 views

Standard gravitational parameter - different formulas

Why we have two formulas for Standard Gravitational Parameter: $$\mu=GM \ \,{\rm and}\, \mu = rv^2 \ .$$ I don't see any direct connection between the two formulas. How can we derive the second from ...
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1answer
60 views

Non-discoveries by the Kepler space telescope: exomoons, co-orbital planets, trojans

I am just reading the review article Advances in exoplanet science from Kepler (arxiv preprint: http://arxiv.org/abs/1409.1595), and I found a remarkable paragraph (last paragraph in section ...
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3answers
66 views

astronomy & light pollution

If you were staring to the sky in a big city and electricity is turned off in a big area around you, would you be seeing the sky with little light pollution instantly?
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1answer
102 views

Is there a way to tell what centile of the overall sample a star's mass is in?

One hears that hyper-giant stars like Eta-carinae represent the upper bound on stellar mass at about 130 solar masses. At the lower end there are red dwarfs with as little as 0.075 solar mass. You ...
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1answer
69 views

How did all of the heavy elements on earth get here?

I have often read that a first generation star went supernova and seeded our solar system. It is well known that stars that go supernova are the source of elements heavier than iron. I guess I am ...
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2answers
131 views

Is redshift a reliable means to know how fast an object is moving away or towards an observer?

Does wavelength change with distance? How do they know that the change in wavelength can only be caused by the change of speed of the object to the observer? What if it is an intrinsic property of ...
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2answers
2k views

Is it possible to 3D print a mirror to create a high quality telescope?

Is it possible to 3D print a mirror with todays available materials? If so, would there be a reduction in image quality?
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1answer
438 views

Ephemeris calculations: Light time correction of the moon

I am currently trying to calculate apparent positions from raw JPL data. I've got it pretty much figured out, but there is one thing that's bugging me: Has the light time correction of the moon to be ...
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1answer
43 views

Simplifying Friedmann's Equation

So we have one of Friedmann's equation: $$\rho_c = \frac{3H^2}{8\pi G}$$ Using This website, resources where gathered for specific times in the universe. The resources being the Hubble constant at ...
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Why does the Zodiacal light vary between dawn and dusk?

According to several pages, in the Fall the Zodiacal light is better seen at dawn than at dusk: In the mid-latitudes, the zodiacal light is best observed in the western sky in the spring after the ...
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1k views

What is the farthest-away star visible to the naked eye?

My girlfriend and I were watching Cosmos, and something Carl Sagan said got us wondering what the farthest-away visible star is. Obviously "visible to the naked eye" is a fuzzy concept that might have ...
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4answers
4k views

Why does Venus rotate the opposite direction as other planets?

Given: Law of Conservation of Angular Momentum. Reverse spinning with dense atmosphere (92 times > Earth & CO2 dominant sulphur based). Surface same degree of aging all over. Hypothetical large ...
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1answer
44 views

Data/signal from a black hole to observe a singularity

I wonder if a situation is possible where, we measure some signal/property concerning a black hole. Supposing the measurement we make with some telescope, gets us the Fourier transform coefficients of ...
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1answer
65 views

Radial and tangential velocities of a star

(source) Early in this piece it states that the radial and tangential velocities are: $$V_r = V_c \cos(\alpha) -V_{c,0} \sin (l)$$ $$V_t = V_c \sin(\alpha) -V_{c,0} \cos (l)$$ but I am struggling ...
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0answers
37 views

Sharpness of starlight

I am interested in argument that the observed lack of blurriness in starlight refutes the "tired light" theories. I have not been able to find this argument expanded in detail. There are two ways ...
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3answers
1k views

Rocky Planet in the center of System [duplicate]

We all know that mostly stars are at the center of planetary systems, but is it possible that instead of star there was a rocky planet in the center with stars (and other planets and moons) orbiting ...
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1answer
79 views

Could a Class A Stellar Engine Use A Brown Dwarf

Could a class A stellar engine (or maybe a class C one) be built using a brown dwarf (for argument's sake, a T-dwarf like Gliese 229B)? Would it be capable of enough thrust to move itself any ...
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6answers
3k views

Where can I find public domain astronomical pictures?

Where can I find public domain astronomical pictures of nebulae, stars, etc. that can be freely used?
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48 views

What can be seen with a 114mm Aperture 675x Zoom Telescope?

I choose to post this question on the physics exchange seeing there would be a bigger audience for answers than the astronomy exchange still in BETA. But i'm looking to buy a telescope and was ...
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1answer
29 views

How much has the Milky Way moved since it's forming?

What i really want to ask how much has the Milky Way moved, relative to where it was "at the big bang" or the soonest time that makes sense (since i doubt "at the big bang" makes much sense in this ...
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2answers
565 views

How did pre-Copernican astronomers accurately predict planetary position?

Copernican elements (circular orbital elements) are not very accurate. But Copernicus simplified our understanding a great deal by placing the Sun at the center of the system. Im astonished by the ...
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0answers
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Sun reaching zenith at a particular latitude

I need to find when the sun reaches the Zenith at a given latitude. What I've done so far: $L=23.5 \cdot \sin(\frac{2\pi}{365.25}\cdot D) $ Here L is the latitude (<23.5) and D is number of days ...
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1answer
278 views

Does it make sense to continue searching for dark matter on Earth?

The Large Underground Xenon Detector (LUX) recently released results1 that they have found no signs of dark matter2 after a ~3 month search this spring and summer. The LUX group plans to spend all of ...
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1answer
114 views

Magnification of an astronomical telescope not in normal adjustment?

I am stuck on this question: A telescope consists of two thin converging lenses of focal lengths 100cm and 10cm respectively. It is used to view an object 2000cm from the objective. What is the ...
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3answers
275 views

Dark age of universe when all fusion process ceases?

Some say we live in the golden age of the universe because there exits countless number of stars that shines in the dark universe. As the supply of gas for star formation is steadily being exhausted, ...
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1answer
2k views

Do all known planets and moons have magnetic field?

In this Wikipedia article it is stated, that magnetic field of Earth is caused by currents in her core. The same origin is for Jupiter magnetic field. For Moon (article) there is a magnetic field, ...
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5answers
981 views

Are telescopes with a concave lens useful for astronomy?

Are telescopes with a concave lens (instead of convex ones) ever useful for astronomy? And if so, where are they used? Do they ever affect resolving power?
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4answers
2k views

Why are there no asteroids or meteoroids with relativistic speeds?

Cosmic rays can have energies going into the $10^{20}$ eV domain. Asteroids and meteoroids originating in the solar system are probably limited in their speed because they all started out from the ...
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Sedna, VP113 and the likelihood of the PX/Tyche/Thelistos hypotheses

The recent discoveries in exoplanetary science (specially those findings of planets orbiting far far away from its parent star/stars) raise questions about how much we know about the (true, AIU ...
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3answers
160 views

How does the evolution of a solar system not break the second law of thermodynamics?

Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck. As I understand it, the solar system evolved from a ...
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1answer
109 views

How is UT1 being computed?

I've recently read up about time standards and now understand that UTC is a second-corrected version of international atomic time so that it is kept within 0.9s from UT1. And then UT1 is defined as ...
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239 views

How to explain the existence of heavier elements in Population I stars and in Population II stars contain lighter one

Recently I read Astrophysics Notes where I found a statement that young stars are classified as Population I stars and relatively older one as Population II stars. Population I stars contain ...
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2answers
176 views

Gyrochronology, the formula is empirical ?

The formula used in Gyrochronology that relates a star's Period of Rotation-Mass-Age is empirical? This news How to Learn a Star’s True Age "“A star’s rotation slows down steadily with time, ...
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How to prove the Hubble law is the unique expansion law compatible with homogeneity and isotropy?

In the book physical foundations of cosmology, it saids that Hubble law is unique and a problem seems to be a hint of proving that. In order for a general expansion law,v=f(r,t), to be the same ...