All Questions

7
votes
1answer
102 views

Timeline of falling into a blackhole

For some "average sized" black hole, how long would it take for a distant (spacesuit-wearing!) astronaut to: be able to see the gravitational lensing with the naked eye clearly feel the gravity ...
4
votes
2answers
149 views

What is the difference between solar wind and solar radiation?

Is there a difference between solar wind and solar radiation or are they just different ways of describing the same thing?
9
votes
2answers
72 views

On (minuscule) dark matter production in supernovae

It is believed that dark matter is made of particles, which interact with matter only weakly and gravitationally. One common candidate for dark matter are so called WIMPs. WIMPs, specifically, are ...
6
votes
2answers
169 views

How does the Milky Way look like above 66° North and below 66° South?

I read on Wikipedia: depending on the time of night and the year, the arc of Milky Way can appear relatively low or relatively high in the sky. For observers from about 65 degrees north to 65 ...
6
votes
2answers
113 views

How to calculate the altitude of the Moon?

With the known latitude coordinate of the observing position, how to find the altitude of the moon when it is high, i.e when it crosses the local meridian?
8
votes
6answers
643 views

Why don't we have 2 Summers and 2 Winters?

Due to Earth's elliptical orbit, its distance from Sun varies by almost 5 million Kilometers (147 million Kilometers at closest point & 152 million Kilometers at farthest point, i.e. almost 3% of ...
4
votes
1answer
76 views

Hypothetical beyond Neptune far away planets orbiting the Sun

The planet HD 106906 b was found at 650 AU from its home star, which is not a star much different from the Sun. Fomalhaut b is also a young planet that is orbiting very far away from its sun. These ...
1
vote
1answer
32 views

How do we know that the intrinsic brightness of Cepheid variables corresponds to their period?

As I understand it, beyond parallax the next way of estimating the distance to astronomical objects is by using a relationship between the period and intrinsic luminosity of Cepheid variables. How do ...
4
votes
1answer
89 views

Lunar Soil : what are those “bumps” and how they were formed ?

I was watching a video of the chinese lunar landing and saw the numerous bumps on the soil. What are they ? Is there any theory to explain how they came into existence ?
3
votes
4answers
313 views

If the hammer and feather move at the same speed why do comet and the tail particles move at different speeds?

From this exhibition by an astronaut on the moon dropping a hammer and a feather and showing they move at the same speed, why do the particles of the comets tail move away from the comet, slow down ...
2
votes
1answer
20 views

In India, what is the best time to view the geminid meteor shower in 2013

As of the time of writing this question, the meteors should have appeared, but so far I haven't seen any. What time would be the best to view them?
8
votes
1answer
88 views

How do we calculate the escape velocity of galaxies?

How do we calculate the escape velocity of galaxies? Do we have to know the total mass? What is the escape velocity for Milky Way?
4
votes
2answers
106 views

What are some night sky objects I could see with my Celestron UpClose 20x50 Porro Binocular?

I bought this binocular because I've read countless times that one should start with a pair of binoculars before diving into telescopes. I've seen details of the moon and I can notice Venus round ...
4
votes
1answer
69 views

What's the smallest scale at which dark matter has been measured?

What is the smallest scale at which we have detected "dark matter" (more kinetic energy than would be predicted)? If you don't mind indulging a follow-up: Would its detection on smaller scales be ...
3
votes
2answers
81 views

Is there an orbit that could cause regular debris showers like in the movie Gravity?

[some spoilers] If you were in the ISS and orbiting the Earth roughly every 90 minutes, would it be possible for debris to be orbiting such that it passes you every 90 minutes? While Neil DeGrass ...
5
votes
1answer
124 views

Why are galaxies disk shaped?

I always see galaxies in "disk" shape in pictures. It is like, there is a rotational movement on a plane and the system is balanced by the pulling-in gravitational force which prevents the stars to ...
5
votes
1answer
61 views

Was comet ISON in a Kepler orbit prior to disintegrating?

Was comet ISON in a Kepler orbit prior to disintegrating? If so, it is possible over time that Kepler orbits can be altered by increases or decreases in the mass of of celestial bodies? For instance ...
3
votes
2answers
757 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
1answer
58 views

Calculate apsides without knowing eccentricity

How would one go about determining the apsides of an orbit, knowing only the current distance between the 2 bodies, the orbital velocity, and the period? Every formula I've seen requires eccentricity, ...
7
votes
3answers
307 views

Is the Jupiter-Sun system considered a binary system of some type?

Since Jupiter is very massive, it is the only planet (in our solar system) that has a center of mass with the Sun that lies outside the volume of the Sun. (Source) If Jupiter was a star, they would ...
9
votes
3answers
213 views

How can the Earth's rotation speed up? [closed]

It is known as a fact that Earth's rotation is slowing every year, that's why we sometimes have 61 seconds long minutes. In the Java documentation of Time : ...
4
votes
1answer
80 views

Brightest Radio Source In the Universe

I would have assumed that the brightest radio source in the Universe is a quasar of some kind (perhaps 3C 273) given that the average pulsar has luminosity of $~10^{40} \text{Watts}$ and this is the ...
7
votes
2answers
32 views

Official registry of lunar placenames?

What's the definitive source for names of geographic objects on the moon? Reason: As a computer graphics project I've rendered a scene based on LROC terrain data. I want to know what I'm looking at. ...
4
votes
2answers
60 views

Is sundial time entirely dependent on solar azimuth?

I've visited several "how sundials work" sites and can't seem to get a clear answer to this: is "sundial time" just a linear function of solar azimuth? More specifically: When the sun is due ...
8
votes
1answer
513 views

Is there any telescope on Earth that can see the lunar rovers on the moon?

If I have the right numbers, it seems to me that even Hubble telescope might barely be able to make out a carcass of a blue whale on the surface of the moon, which puts objects as small as the lunar ...
5
votes
1answer
47 views

How can absolute value of azimuth exceed distance from pole?

I'm sure I'm just doing something dumb, but: Yildun has a declination of approximately 86.5. This puts it 3.5 degrees from the celestial north pole. Per the snapshot below, Yildun's azimuth can ...
4
votes
2answers
98 views

How many minutes does a sundial change every day?

I'm planning to create a sundial in Ghana (10° 28.852', 0° 26.032') in July 2014. I will stay there for about 3 weeks. Do I need to adjust the numbers anywhere in these 3 weeks? I know the shadow's ...
6
votes
1answer
75 views

Where did Mars water go?

Many sources indicate that there is ice water on Mars today, but it is mainly traces, here and there, but not that much. However, solid hypothesis state that there were oceans on Mars, see ...
3
votes
1answer
76 views

Coordinate transformations between reference frames in spherical astronomy

Suppose there are two observational frames of reference with origins $O$ and $O'$, respectively, separated by some constant distance. A body located at point $P$ has Cartesian coordinates ...
11
votes
3answers
178 views

Is it possible to measure galactic red shift using consumer telescope equipment?

I was wondering if it would be possible to measure red shift from distant galaxies using consumer grade telescope equipment and spectroscopy filters. (like this one) I imagine it would require a ...
6
votes
1answer
58 views

What are the current accepted theories of the formation of the Uranian moon Miranda?

Miranda, a moon of Uranus is unique in that it has a very fractured surface Source: University of Oregon The surface is said to be jagged and fractured, with comparatively large disjointed cliffs ...
8
votes
3answers
225 views

Is the rotation of the Sun and the rotation/orbit of the Moon around the Earth a coincidence?

While looking at sunspot information in connection with Amateur Radio, I found that the Sun rotates on a period from 27 days to 31 days. Its rotation is differential, at the equator it spins at a ...
4
votes
1answer
701 views

How to measure the altitude and azimuth of a star?

Given that the star is crossing the local meridian line in a certain location, I've tried calculating the altitude of a star by finding the difference between the declination of the star and the ...
5
votes
1answer
43 views

Is there a pattern between the mass of a body and the mass of orbiting objects around it?

I was looking at Wikipedia's Solar system page, and it says that Sun represents 99.86% of the whole solar system mass. I found that pretty huge. So i calculated ratio of masses : Earth / (Earth + ...
3
votes
2answers
196 views

Why do the planets in the Solar system stay in the same orbital plane?

An earlier question addressed why all planets formed in the same orbital plane, but how is this angle maintained? What prevents the planets from taking on a different orbital plane?
8
votes
1answer
211 views

How do people measure the distance between the earth and the moon?

How do people measure the distance between the earth and the moon? What methods were used? Where can I find the official data?
9
votes
2answers
91 views

What is the current accepted theory as to why Titan has retained its atmosphere?

Titan (moon of Saturn) is unique in that it possesses a very thick atmosphere. However, Titan is certainly is not the largest of the moons - Ganymede being larger. What is the current accepted ...
0
votes
1answer
716 views

How to build a powerful home made telescope [closed]

Simple, I fell in love with the sky when my parents were constructing our new house I was a kid then and one day I ventured out on the terrace, to my amazement it was a full moon, ever since I've felt ...
0
votes
3answers
106 views

What is the formula to figure out how far away a star is? [duplicate]

I have tried to search for this but it won't show me the formula or "how to" figure out the formula. So what is the formula, and how do you figure it out? (The formula for stars within 400 light ...
5
votes
1answer
103 views

How do scientists know there are about 300 billion stars in a galaxy and there are about 100 billion galaxies?

Just to think about this is mind boggling. But how do scientist get these numbers? What technology/system/theory do they they use?
5
votes
1answer
80 views

Are there any alternative explanations for the gravitational force we attribute to dark matter?

It always seemed counter-intuitive to me that we observed an measured a gravitational force and since the universe has not enough mass to account for it, the conclusion was to say there's a different ...
6
votes
1answer
159 views

Does anyone know why three of Jupiter's largest moons orbit in 1:2:4 resonance?

Three of the first four moons ever discovered outside of our own planetary sphere of gravitational influence orbit in very close to perfect resonance. Europa's orbit is almost exactly twice as long as ...
4
votes
1answer
49 views

Source of T Tauri wind?

What particularly causes the T Tauri star to eject the strong bipolar wind which clears the gases around the star?
12
votes
1answer
261 views

Could any known, living organisms on Earth survive on Mars?

No life has been discovered outside of Earth (yet?), but do we know if anything that would be considered "living" on Earth could conquer Mars? (or maybe Venus?) With the Mars One project on the way, ...
2
votes
1answer
29 views

iteration to cover the whole sky with right ascension, declination, angle

I am sure I get parts of the terminology wrong but if anyone can shed some light in the following: I understand that for a given right ascension (RA) and declination (DEC), one has defined a ray ...
5
votes
4answers
198 views

How do you define the diameter of the Sun

That is, it's twice the radius where the radius is from the centre of the sun to some edge. But what is that edge?
11
votes
2answers
284 views

At what distance from Earth would our Sun be the same apparent magnitude as the next brightest star in the sky?

When I stand outside looking at the night sky, to my untrained eye, everything except the moon looks like a star. I know intellectually that some are planets circling our sun, and some are entire ...
4
votes
3answers
116 views

Find distance from star to star?

How do you find the distance from a star/planet/black hole to another? I know people can calculate the distance from Earth to a star, but what about from one to another?
2
votes
2answers
119 views

Has life been discovered outside of Earth?

I've just watched a movie that made me curious as to whether life has really been discovered on another world such as Europa??
8
votes
1answer
57 views

How was Io not torn apart by tidal forces during its formation?

Jupiter's moon Io is arguably one of the most volcanically active bodies in the Solar System. The reason, according to NASA's page Scientists to Io: Your Volcanoes Are in the Wrong Place is believed ...

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