2
votes
2answers
72 views

Which is really larger, Big Dipper or Small Dipper, in 3D

If we take the convex hull of the 3D coordinates of the stars in Ursa Major and Ursa Minor: which hull has larger volume? This is meant semi-humorous but we might also learn some interesting points ...
0
votes
1answer
76 views

Can the Sun be used as a point source of light to achive better focus?

There's a limit to how well sunlight can be focused by a parabolic reflector or a lens because the Sun is not a point source. I wonder if the sunlight could be engineered to work as if it was (much ...
7
votes
2answers
110 views

Recommendation for introductory cosmology text

I am looking for recommendations for an introductory text (or texts) on cosmology on the advanced undergrad or beginning grad level. I am coming from primarily a physics undergrad background (doing ...
3
votes
1answer
1k views

Average amount of annual daylight at any place on earth

If this is the wrong group please direct me to the correct one. It seems intuitively obvious that the amount of daylight per annum should be the same for any latitude on earth. For example, 12 hours ...
11
votes
2answers
105 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 ...
3
votes
1answer
301 views

Black Hole / Hawking Radiation: Why only capture anti-particle?

I may have some specifics wrong here. If so, don't focus on those. Just focus on the general thrust of my question. I "understand" (cough) that particle/anti-particle pairs form spontaneously in ...
1
vote
1answer
241 views

How big is the universe. How does it works?

I watch this movie: How big is the universe https://www.youtube.com/watch?v=b34gwCKIM50#t=50m00s I can't understand where is there triangle with 180 degrees. What exactly is this red spot on the ...
3
votes
2answers
118 views

Why do we think that there is no two-solar-mass black hole?

We think that the mass boundary between neutron stars and stellar mass black holes is around three solar masses. The maximum mass of the neutron stars now is two solar masses and we may find a 2.6 ...
2
votes
1answer
83 views

If Mars orbited the Earth how distant would it have to be to cause the same tides?

If it were possible to replace the Moon with Mars, how distant would it have to be to essentially create the same oceanic tides as the Moon currently does? Mars seems to be roughly 3 times the mass of ...
2
votes
1answer
72 views

What is $v_{GSR}$

In this paper ("The Apache Point Observatory Galactic Evolution Experiment: First Detection of High Velocity Milky Way Bar Stars") they plot and calculate $v_{GSR}$. $GSR$ stands for Galactic Standard ...
9
votes
3answers
394 views

Why are orbits elliptical instead of circular?

Why do planets rotate around a star in a specific elliptical orbit with the star at one of it's foci? Why isn't the orbit a circle?
2
votes
2answers
43 views

Pulsars with accreting disk in binary system

Following this line, I am wondering about the following question. Accreting pulsars in binary systems are usually thought to accrete from a prograde disk, so increasing their spin in the process. ...
3
votes
1answer
95 views

Are there are any photographs online that approximate what the Milky Way looks like to the unaided eye?

I love seeing all the long-exposure photographs of the Milky Way, but I'm going to Cherry Springs State Park in Pennsylvania next month, and I'm wondering if there are any photos that approximate what ...
1
vote
1answer
72 views

Orbital Elements Transformations

I'm a third year undergrad, and for the project I'm doing this summer, I need to figure out the Earth's position and velocity from the moon's point of view. From the reading I've done, it seems like ...
3
votes
2answers
126 views

Is the Sun homogeneous?

Does the Sun have the same composition and density everywhee within it? How does it vary in other stars?
5
votes
0answers
72 views

Is it possible to have two objects moving by sum speed of light (c) in the opposite direction? [closed]

I am puzzled by this question, because by the laws between the two object the relative gravitation force should be infinite. Anyways we can take two objects where the sum of speeds are equaling c ...
1
vote
0answers
156 views

How can I calculate what star was above my head when I was born? [closed]

Almost everybody knows the concept of Zodiac. But there are others. And, AFAIK, even Zodiac classification is wrong for nowadays - since the classification of the people's Zodiac Sign was developed ...
2
votes
1answer
76 views

Why do we not send diggers to Mars if we think there's underground water?

A friend of mine asked me this question: If we have a guess that there may be underground water on Mars, why do we not send rovers with diggers? I do have a few ideas, but I want alternative ...
3
votes
1answer
103 views

What is the optimal escape trajectory from near a black hole?

Consider a space ship that is being drawn closer to a black hole. The crew begins to notice the effects, and discovers that they are nearing the black hole. They then manage to halt their ...
2
votes
1answer
16 views

Term for a momentary geometric pattern formed by astronomical objects

Few days back, the Pleiades, the Sun and the Moon were forming an almost perfect equilateral triangle. Is there a term that describes such momentary geometrical patterns? ...
3
votes
0answers
20 views

Any new info about solar flares hitting the Moon added by the LADEE mission?

This article from 2011 mentions simulations about the sputtering effect caused by a solar flare hitting the Moon: "We found that when this massive cloud of plasma strikes the moon, it acts like ...
3
votes
2answers
152 views

Why are spacecraft not air-launched from airplanes

I searched on the subject, thinking it could probably be cheaper to fly the spacecraft aboard a plane and then launch it from altitude. The only thing I found was this Wikipedia page, but it only ...
1
vote
2answers
77 views

What is the difference between LMC and SMC?

Apart from the obvious difference as suggested by their names that the Large Magellanic Cloud is 'larger' than the Small Magellanic Cloud, what are the other differences between them? Do give all the ...
8
votes
1answer
138 views

Blowing up an asteroid/comet really potentially worse?

Often on television shows and in articles I see it mentioned that it'd always be bad to blow up an asteroid or comet because then the energy would just be spread out and cause even more damage. ...
2
votes
2answers
95 views

What is meant by “Radial Direction” of a galaxy?

There is a scientific journal article having a line: "In order to study the star formation scenario in the radial direction of the LMC...." What is meant by 'radial direction' of a galaxy ?
2
votes
1answer
69 views

What percentage of visual stars are actually binary stars?

I know this is such a thing as a binary star where for example two stars rotate around a central point of gravity but to the naked eye are just a star. What I do not know is how common this is ...
3
votes
2answers
1k views

How to calculate Longitude from Right Ascension?

Considering that a star of certain declination is crossing the local meridian at the observer's zenith at an unknown location on the earth. Here, the declination of the star is equal to the observer's ...
2
votes
2answers
29 views

Why the lows of the GRB 2014-04-27 in Andromeda?

The Swift gamma ray burst space telescope has measured a GRB according to the link below. But why the oscillations in the measured gamma rate? Why wasn't just an increase detected, but also as big ...
2
votes
1answer
55 views

Did the Babylonians believe in the Heliocentric version?

It's mentioned that the Babylonians decreed that there were exactly 360 days in a year. This statement was based upon the utilization of 360 as a standard (based on the sexagesimal system) i.e., they ...
1
vote
0answers
31 views

Torus of the AGN

How much do we know about the structure of the torus surrounding the galactic nuclei? Is the shape defined or still under speculations? And are there different structures for this torus possible i.e., ...
5
votes
2answers
268 views

Why is twilight longer in summer than winter and shortest at the equinox

I recently decided to set my alarm clock to wake me up when it is "dark" out. In the end, I decided to set my clock to the earliest time that nautical sunrise is in my state (Illinois) and stick with ...
4
votes
1answer
78 views

What study profiles could land me the job of Astronomer?

I realize there are very few to none universities that offer direct specialization of Astronomy. If I aspired to be make astronomy my career choice, I'd likely have to pick something like physics and ...
4
votes
2answers
74 views

What are shooting stars and how are they formed? [duplicate]

What are shooting stars? How are they formed and how often do they occur during the night? Also, why are there more shooting stars on some nights than on others?
3
votes
1answer
74 views

How would a planetary defence against comets work?

Mappings of practically all potentially dangerous asteroids is well underway. But comets seem almost hopeless to protect against. How far away are approaching comets detected today? How long time ...
13
votes
1answer
207 views

How exactly does inflation convert random gravity fluctuations into coherent gravitational waves?

In the course of this very enjoyable press announcement, it is mentioned that inflation can create gravity waves by amplifying gravity fluctuations. I do not properly understand this statement. I ...
4
votes
1answer
36 views

Calculating Angular Distance

Given the horizontal coordinates of two objects in the sky, how does one go about calculating the angular separation between them?
3
votes
1answer
58 views

Triple Stars v/s Ternary Stars

Ternary (or trinary) stars are not the same as triple stars. So, what is the basic ...
5
votes
2answers
81 views

Are Gamma Ray Bursts of galactic or extragalactic origin?

I read about the 1995 Lamb-Paczynski debate on whether GRBs are galactic or extragalactic in origin. With our current experimental evidence, have we found whether GRBs are galactic or extragalactic?
2
votes
1answer
47 views

How can pre-main sequence stars radiate more energy than main-sequence stars?

How can a pre-main sequence star radiate more energy by gravitational contraction than a main-sequence star can by hydrogen fusion?
3
votes
2answers
107 views

Why do pictures of the Milky Way look like a spiral?

When I see pictures of the Milky Way they show a spiral shape. Why is this?
4
votes
1answer
37 views

Active Galactic Nuclei - categorisation on the basis of observer?

As we know AGNs are considered to be one of the most luminous objects to be found in the cosmos.Based on the observer, for instance on Earth, we categorize them on the basis of the angle between the ...
3
votes
1answer
54 views

Instrument aperture sizes on Hubble Telescope

When looking at the diagram of the focal plane of the Hubble Space Telescope I noticed that the aperture sizes of most of the scientific instruments are very small. They occupy a very tiny fraction of ...
3
votes
1answer
70 views

Taking Advantage of Time Dilation

According to Einstein's theory of Special Relativity, one's speed in relation to a relatively stationary object would 'slow down' time on the moving object. With this in mind, would it be possible to ...
4
votes
1answer
24 views

2SB mixer in radio astronomy?

In literature about the instrumentation of radio astronomy, I frequently come across a type of mixer described as "2SB". I'm familiar with single-sideband (SSB) and double-sideband (DSB) mixers, but ...
6
votes
1answer
68 views

Calculation of Horizontal Coordinates

Given a fixed coordinate location on Earth (i.e. a latitude and longitude), and a fixed equatorial coordinate location of a particular astronomical object in the sky (i.e. right ascension and ...
2
votes
2answers
214 views

Where is a Hollow Object's Center of Gravity? [closed]

Let's imagine that the Earth's moon is hollow. Given this scenario, where would its center of gravity be? What would the conditions be like at the center? Also would one still be able to stand on the ...
2
votes
1answer
144 views

Meaningful theories of the shape of the universe

Normally, when people say "the universe is infinite" they generally mean something like "the observable universe is locally flat, it is easy to assume that it is flat way beyond the observable ...
1
vote
2answers
97 views

What does “Normalized to Si 10 to the power 6” mean?

I'm writing a space game that I want to give a more "realistic" feel. When looking for a reference as to distribute elements in planets (for mining, etc) Instead of finding the more usual percentage ...
1
vote
2answers
53 views

Do origin theories imagine each planet to first orbit the Sun very irregularly before stabilizing?

What I was wondering is that, for example, toss a few balls into zero gravity space randomly, what would be the steady state motion? Would not all the balls go on weird directions and undergo ...
-2
votes
1answer
88 views

Active Galaxies

I've read that there are 4 distinct although related forms of AGs : Seyferts, Quasars, Radio and Blazars. Are there any other forms possible? Also do these forms ever intermix to give something new?

15 30 50 per page