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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2answers
583 views

Differences between astronomy, astrophysics and cosmology? [closed]

What is the main difference between Astronomy, Astrophysics, and Cosmology? I have the impression that astronomy is a subject that runs parallel to physics but it is outside the physics field. This ...
4
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1answer
74 views

How do scientists estimate elemental-abundance in the universe?

I understand how cosmological observations can estimate the amount of 'baryonic matter' in the universe, but what I don't understand is how scientists can estimate the abundance of a particular ...
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0answers
68 views

Algorithm for calculating lunar crescent visibility

Is there a simple algorithm for predicting lunar crescent visibility. Simple enough to do with a calculator at least. Those offered in Meeus' Astronomical Algorithms are a bit too involving to do by ...
1
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1answer
72 views

What will I see if I travelled to a distant planet in 100 times faster than speed of light and look back? [closed]

Consider this scenario. I enter a space ship at 10:00 AM, it starts to move at a speed 100 times faster than light, I travel for 55 mins. And then slow down to very much less than speed of light and ...
12
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2answers
149 views

What is the most distant object from the Earth that a spacecraft has visited to date?

What is the most distant object from the earth that a spacecraft visited has visited so far? What was the mission and when did it happen?
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0answers
64 views

Simplified calculation to find Lagrange point L1

I'm trying to find the position of Lagrange point L1 in the earth-moon system. To make the whole thing easier (I thought) I don't care about the sun's influence or any other forces than the ...
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3answers
420 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 ...
2
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1answer
46 views

Prerequisites for Ptolemy's Almagest

I hope this is a valid question to ask on this website (since it's astronomy and not e.g. mechanics, I wasn't so sure). What prerequisites are needed for fully understanding Ptolemy's Almagest. Fully ...
3
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1answer
82 views

Is the best data about Mercury's perihelion shift really 60 years old?

The advance of the perihelion of Mercury is one of the four classical tests of general relativity. I wonder what's the most precise modern measurement of it. However, while scanning the literature, ...
5
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2answers
107 views

Are comets known to exist in other star systems?

Are comets a feature unique to our Solar System? Or, are comets/cometary clouds detected around discovered/observed extra-solar systems too? If they were detected elsewhere, how do such cometary ...
5
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2answers
146 views

How do we estimate $10^{23}$ stars in the observable universe?

Now, I read somewhere, that there are $10^{23}$ stars in the observable universe. How did scientists estimate this?
3
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5answers
11k views

Having difficulties finding objects with Celestron Telescope

I have a Celestron Astromaster 114 EQ, which I saw was highly recommended as a great beginner scope. But I just can't seem to find anything in the sky with it. Yes, I've removed the lens cap, yes I've ...
5
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1answer
63 views

What fraction of baryonic matter is in stars?

We know from big bang nucleosynthesis that baryonic matter accounts for about 5% of the universe's total mass-energy density. What is the current best estimate of how much of this is in the form of ...
2
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2answers
341 views

Calculating the time of dawn

Knowing that astronomical twilight (i.e. astronomical dawn) is when the sun is 18 degrees below the horizon, I am calculating the astronomical twilight time this way: ...
14
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1answer
1k views

How would one detect antihydrogen in the universe?

Since the spectra of hydrogen and antihydrogen are the same, how do astronomers know which one they're detecting? Is, perhaps, the Lamb shift in antihydrogen different?
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4answers
8k views

How do astronomers measure the distance to a star or other celestial object?

How do scientists measure the distance between objects in space? For example, Alpha Centauri is 4.3 light years away.
2
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1answer
65 views

How the distance and diameter of the stars are experimentally measured?

How to measure the distance of a star and the diameter of it from earth based tools? Normally we can measure the angle between the stars edge. But diameter or distance needed to measure the other ...
1
vote
1answer
27 views

Interferometry works as a filter

I attended an astronomy seminar the other day and though I did not pick up much as it was on data collection etc, I did take away one sentence: "Interferometry works as a filter" Now I know what ...
0
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1answer
47 views

How to find how far away could a binary system be? [closed]

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 ...
0
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0answers
23 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 ...
5
votes
1answer
151 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)
0
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1answer
47 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 ...
6
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3answers
203 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 ...
1
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3answers
107 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 ...
12
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2answers
375 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 ...
6
votes
6answers
573 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: ...
2
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1answer
211 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 ...
0
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1answer
129 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...
3
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1answer
432 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 ...
1
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1answer
82 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 ...
3
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1answer
106 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 ...
2
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1answer
346 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 ...
1
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2answers
135 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 ...
14
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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?
0
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1answer
59 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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0answers
15 views

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 ...
11
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2answers
3k 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 ...
11
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4answers
5k 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 ...
1
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1answer
54 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 ...
1
vote
1answer
92 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
41 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 ...
2
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1answer
80 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 ...
11
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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?
0
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1answer
41 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 ...
6
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2answers
727 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
42 views

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 ...
1
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1answer
197 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 ...
3
votes
3answers
340 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, ...
9
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1answer
3k 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, ...
27
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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 ...