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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What is the angular distance between Ptolemaic perigees of Mercury?

In his excellent treatment of the history of the science of astronomical distances and sizes, Albert van Helden says (p.29) that The complicated [Ptolemaic] model of Mercury has the curious ...
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12 views

What is the definition of the “stellar angular diameter” in stellar astronomy?

(Following the definitions here: http://arxiv.org/pdf/astro-ph/0509535.pdf ) What is the "stellar angular diameter", as measured by astronomers specializing in stellar astrophysics? Using the ...
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16 views

Using stellar spectroscopy to measure stellar parameters, why is it log g?

Stellar spectroscopy can in principle measure the stellar surface gravity, radii, effective temperature, and stellar rotation. Why is it that surface gravity g is ...
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48 views

What is Drake equation?

I was reading an article on aliens, where I found something called Drake equation. I tried to understand it, but just couldn't get it in my head, as I belong to class 11. So, can anyone explain me it ...
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8 views

Do the arms of spiral galaxies differ based on the speed of which the galaxy is rotating?

If I were to take a circle with strings attached to it and spin it, the strings would behave differently based on how fast the circle is rotating. Do galaxies behave the same way?
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26 views

Do rotating magnetic fields violate all physical rules? [on hold]

Differential rotation winds toroidal magnetic fields, and is a key for understanding stellar dynamos. At the equator of our Sun the average angular rotational speed is 25.75 days (= 13.980582 ...
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1answer
43 views

Can 4 colinear planets exist?

Imagine 4 planets, A has moon a and B has moon b. A and B are binary planets. Is it possible that a and b and A + B all have same the period, so that the 4 planets are colinear?
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2answers
269 views

Was Leverrier-Adams prediction of Neptune a lucky coincidence?

According to historians both Adams and Leverrier used Bode's law to guess the distance to Neptune, which led to a vast overestimation of its orbital period (Adams - 227 years, Le Verrier - 218 years, ...
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2answers
5k views

Why are gold mirrors yellow?

Why are golden mirrors yellow? Do they add a yellow component to the spectrum or absorb non-yellow components? If they absorb, then why are they used in telescopes being imperfect? If they add a ...
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2k views

What is the largest observed celestial body?

I'm not referring to phenomena such as galaxies or clusters but rather, what is the largest discrete celestial body that has been observed in the universe?
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1answer
25 views

How to calculate tide times?

How do I calculate the time of the tides at a given location? I'm not interested in the amplitude of the tides, just the times when they occur.
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1answer
19 views

Definition of a Supercluster

A group of astronomers in September 2014 redefined what classifies a supercluster. Before this, the supercluster where the Milky Way resides was the Virgo Supercluster. Now, the Virgo Supercluster ...
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33 views

Best telescope for value per dollar? [closed]

recently I'm thinking of buying a telescope for recreational purposes. I'm looking for telescopes that have the highest performance/cost ratio, and I'm willing to spend around $200 on this. Anyone ...
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48 views

Thomas precession and neutron star accretion discs

Assuming, based on this wikipedia article Accretion Discs That accretion discs surrounding neutron stars are composed of a gas and / or plasma. That the accretion disc material can achieve a ...
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1answer
31 views

How to begin using SDSS data?

SDSS has gone through so many updates, it's difficult to find out how to access the data today in 2015. How can I use SQL and Python to access SDSS data, e.g. the photometry and spectra of quasars, ...
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1answer
65 views

If the Sun were smaller but had the same surface temperature, would it still have the same luminance?

Let's assume we have two stars that have the same surface temperature but very different size. I understand how luminosity depends on surface area so the two stars will have different luminosity, but ...
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2answers
54 views

If planet orbits are in the shape of an ellipse and the sun is a focus, where and what is the focus? [duplicate]

I've studied ellipses. I've studied physics. But when it comes down to the elliptical orbits of the planets is where I get confused. Ellipses contain two foci — and in the orbits of our solar system ...
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0answers
14 views

How do exoplanet surveys precisely measure stellar properties?

All measurements in exoplanetary studies (e.g. the Kepler study) depend on how precisely we know the properties of a star. For instance, the planet mass and radius is known only as well as the star's ...
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2answers
1k views

What planets are visible to the naked eye from Mars?

Here on Earth we are blessed with being able to see some other planets, Mars & Venus etc, with the naked eye on a fairly regular basis thanks to the distance between the planets. What about from ...
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4answers
65 views

Navigating to a distant star

Suppose I have a space ship that can travel at $0.9c$, and I'm going to a star located at 20 light years or so from the Sun. From a practical point of view, if I keep pointing the nose of my space ...
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4answers
389 views

Shapes of galaxies

I've heard most of galaxies are spiral or ellipsoid shaped. Is it true? If true, then why they form in such shapes? How did arms of the spiral galaxies form?
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8answers
8k views

Why can't we see light travelling from point A to B?

Let's say we have a cloud of dust which is a lightyear across and someone shoots a beam of light from point A to B , why it is not possible for an observer far far away to see the light while it ...
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2answers
37 views

How do we tell the CMB apart from other radiation?

Say I want to observe the CMB and the CMB only. I point my device (telescope in some frequency range) at the sky and start looking. How do I know it should be in the Microwave spectrum? How do I ...
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3answers
3k views

Are Hubble Telescope Images in true color?

Like many others, I have marveled at the images made available from the Hubble Space Telescope over the years. But, I have always had a curiosity about the color shown in these images. An example is ...
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47 views

Planetary alignment of the gas giants?

There is this nice and new applet of the orbits of the planets around the sun: Solar System Orrery You can click and drag any planet and watch their relative orbits evolve in time. I was curious ...
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5answers
2k views

Does the Moon's core still contain significant heat?

On earth, using earth-sheltering techniques can significantly reduce the temperature fluctuations on a structure. Would the same statement be true as well on the Moon? Does the Moon's core still ...
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24 views

Why do TiO bands dominate M dwarfs?

I'm new at understanding stellar classification and the spectral classification of stars. What is the exact reason TiO molecules (titanium oxide) dominate the spectrum for M dwarfs? How did this TiO ...
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1answer
263 views

Why is the Hubble Space telescope able to see farthest in the universe?

What determines how far a telescope can see in the universe? How does recording data for a very long time (~10 years) help? If we could build a telescope which work at microwave region, will it be a ...
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1answer
87 views

Is there uncertainity of position of the perfectly homogenous radiating body?

I heard the standard interpretation of Heisenberg Uncertainty Principle: Just the measurement affects the position of the body because always you want to see a body (=to measure the position), you ...
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1answer
26 views

Detecting molecules in space?

http://www.forbes.com/sites/alexknapp/2012/02/24/nasa-detects-solid-buckyballs-in-space/ I refer to the above article, which mentions that buckyballs "far smaller than the width of a hair" were ...
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3answers
71 views

Why do telescopes move synchronously?

Here's a very nice video (see it in HD) of timelapses captured at the atacama desert. In the beginning of the video you can see that 4 telescopes move synchronously. Could anyone explain why? I always ...
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2answers
1k views

Do we know what event caused the Sun and Solar System to form?

Some stellar formation theories suggest that stars are formed by shock waves from trigger events such as supernovae. This excerpt from Star Formation basically gives the background to my question: ...
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1answer
119 views

How is “little $h$” measured in cosmology? The dimensionless parameter from the Hubble constant, $H_0$

Hubble's law has been well-know for close to a century now. It is written as $v = H_0 d$ where the Hubble constant $H_0$ is the constant of proportionality between recession speed $v$ and distance ...
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0answers
40 views

What are some of the observable effects of black holes

Is there some kind of of observation of a black hole (or a black hole candidate) which could be made from earth, and which might be able to distinguish between two Black Hole models? (1) the classical ...
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1answer
39 views

Is it possible that a satellite once was a small planet?

Very common fact that a planet has satellite which revolves around it and has an impact on that planet too.Is it possible that a small planet had been bombarded with a big planet and transformed ...
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1answer
56 views

What is this big, white, dense, circular collection of stars in this picture taken from a Telescope? (See the image)

I was visiting this website- http://crest.iiap.res.in/iaonightcam.html, where there was a picture of the night sky coming live from a Telescope. My question is, why is there so many stars in this ...
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1answer
51 views

Calculate which star is at Zenith using my latitude, longitude, and time

I'm developing a Planetarium software and I have no idea about how what stars and planets are visible today (mm/dd/yyyy hh:mm) given a latitude and longitude. Reading this tutorial, I have found how ...
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5answers
74 views

Superheavy… “Stars” production of super heavy elements w/o solar fusion

Just a soft question: Let's say a field of stars all die within a short amount of time. Just for argument's sake they produce a debris field of iron ( or any other heavy element). Provided that ...
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1answer
31 views

Observations of erratic rotation of asteroids

An asteroid generally has an irregular shape, therefore, one would expect its rotation is quite erratic in some sense. Are there any observational examples?
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1answer
34 views

Is surface brightness constant as a function of distance?

Well of course it is - the flux drops off as the square of the distance, but the solid angle subtended by the source drops off the same way, so surface brightness is constant, right? Yet other ...
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2answers
95 views

Explain relationship between angular diameter distance and luminosity distance, Etherington Theorem

I have a question relating to the Etherington Theorem. The luminosity distance is defined by the equation for flux, i.e. $F=\frac{L}{4\pi D_L^2}$ where flux is in units energy per unit time ...
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1answer
464 views

What is the status of existing measurements of the speed of gravity?

In replying to a recent question I stated: Gravitational waves have not been yet experimentally observed so as to have their velocity measured. Which after the fact prompted me to try and verify ...
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2answers
999 views

Which way does a black hole spin?

As far as I understand, and from what I have been shown in renderings of black holes, they spin (like water going down a drain). My question is, firstly, does the matter being pulled into a black ...
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2answers
165 views

Is there a confirmation of dark matter signal?

Dark matter, as we know does not emit light, so confirmation of its presence is indirect. Are there any recent indirect confirmations of dark matter. A place one would look for in detecting dark ...
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1answer
37 views

Sol Lagrange points

Where are the Sol-Sagittarius A* Lagrange points, what is located there, have we ever focused a telescope to look? And the larger question, could the existence of these points offer some explanation ...
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3answers
476 views

“Reverse engineering” of a horoscope?

I'll start with a disclaimer -- this is not a question about astrology itself, I'm neither trying to refute nor to defend astrology. I'm interested in purely technical things, which are mostly ...
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1answer
80 views

How can we see objects that are so far away? [duplicate]

The HUDF used to be the deepest image of the universe ever taken by the Hubble telescope, the furthest star in this image is 59000 light years away. The star in question: Now Imagine a light ...
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1answer
58 views

What is the safest distance to create a star? [closed]

What is the safest distance we could create a star without affecting the gravitational force of our solar system? Thanks.
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1answer
46 views

Effect of dark matter on measuring our weight

We know that 95% of the matter in the universe, and all around us, and in our room is dark matter. Dark matter does interact with normal matter only through gravitation. So, does it have an effect on ...
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1answer
42 views

Do stars produce spatially coherent light? Why?

If I understand correctly, the existance of astronomical interferometry implies coherence of light produces by stars. The temporal coherence can probably be achieved by wavelength filters. But what ...