4
votes
2answers
156 views

How does the appearance of the analemma vary with latitude

How does the appearance of an analemma vary with latitude? This what I take to be a definition of an analemma: If the position of the sun is plotted or photographed at noon clock time (say UTC) every ...
2
votes
3answers
92 views

infinite Universe [duplicate]

I was watching a documentary and they said that Cosmologists have determined that the Universe is infinite. I find this to contradict the expansion theory. If the Universe had a starting point then ...
1
vote
0answers
63 views

Why does spectral class and U-V colour correlate slightly differently for main sequence, giant and supergiant stars?

In this diagram the $x$-axis is spectral type for stars and the $y$-axis is B-V colour. Taking Series 1 as the Main Sequence, Series 2 as Giants and Series 3 as Super-giants. Why the spectral class ...
2
votes
1answer
82 views

Has the most luminous object in the universe been found?

It's hard to search through the entire (observable) universe, but the most luminous thing there is must on the other hand be easy to find. Can we now say that the most luminous quasar we know, is the ...
3
votes
1answer
136 views

What you would see in a wormhole?

Science fiction seems to depict the experience of traveling through wormholes (if possible of course) as seeing psychedelic colors or lines of light where stars once were (ie. 2001 or Contact). I ...
3
votes
1answer
122 views

Is the mechanism of solar flares on red dwarfs and brown dwarfs the same as that on the Sun?

The Sun has solar flares that are caused when there is a magnetic reconnection in the Sun's atmosphere, causing a loop of magnetic field to be ejected at high energy, along with a large number of ...
5
votes
1answer
53 views

Diameter of Astronomical Object Using Magnification

I took a picture of Jupiter through my telescope, using an iPhone. I know the magnification of the telescope lens I used, and can Google to get the magnification of the iPhone lens (the magnification ...
1
vote
0answers
35 views

Extra dimensions [closed]

String theory, Kaluza Klein theory etc. need extra-dimensions. For string theory these are compactified. My feeling is that these extra dimensions are not of our 4-D space, but are only of the space ...
2
votes
2answers
77 views

When is Gamma Draconis closest to the zenith in London on April 4th

I am reading Roobert Hooke's paper An attempt to prove the motion of the earth from observations (1674, faksimile). Hooke writes The principal dayes of doing which will be about the 4 of April, ...
3
votes
2answers
115 views

How do rogue planets orbit around stars in other planetary systems?

I got some interesting answers for What would happen if a rogue planet hit one of the planets in our Solar System? But I have seen some documentaries that state that rogue planets from other ...
1
vote
2answers
51 views

can we use connect a long pipe with space station and use vacuum for fuel transfer? [closed]

We all know that we need a lot of fuel to escape from earth. Even 90% fuel of an spaceship is wasted in escaping the earth which definitely affect our power to explore the universe. we have to do a ...
4
votes
1answer
59 views

What places on Pluto and Charon are facing each other?

What places on Pluto and Charon are facing each other? Are Pluto and Charon perfectly tidally locked, or is there a slow rotation over time? And how long after formation should they have become ...
2
votes
1answer
99 views

What is the bulk Lorentz factor?

When we are talking about relativistic motions, say from a relativistic jet, what is meant by the term "bulk Lorentz factor", and the bulk speed, $\beta$?
3
votes
2answers
58 views

Luminosity of black hole accretion disc

The luminosity of a black hole accretion disc gaining mass at a rate $dM\over dt$ can be estimated as ${1\over 12}{dM\over dt}c^2$ That is a substantial proportion of the rest mass of the in-falling ...
1
vote
1answer
162 views

If the Universe is infinite, would heat death be impossible?

If the Universe is infinite, one would imagine that if we kept moving through space, we'd constantly find newer and newer galaxies and objects forever. This would imply that there is an infinite ...
3
votes
2answers
87 views

What are the stars/constellations a beginner/enthusiast can easily identify?

I was just wondering what are some of the stars, constellations or any other things that one can just identify by looking up at the night sky. For example, when ever i look up, I immediately see ...
1
vote
1answer
108 views

Conversion of magnitudes to Jansky and MAGPHYS?

I'm a bit puzzled and not an observer, so please bear with me if I'm being stupid here. The code MAGPHYS specifies Jansky (Jy) as the input unit for flux through ...
1
vote
2answers
91 views

Are objects in the universe moving away from each other at the same acceleration?

This is a follow up question to Does the universe expand at the same rate everywhere in the universe?. If the universe is expanding, then it would seem necessary for each object (ie galaxy) to be ...
4
votes
0answers
80 views

Is there an upper limit to the mass of terrestrial planets

The exo-planet Kepler-10c has a mass between 15 and 19 times the mass of the Earth (making it comparable in mass to Neptune), and yet is thought to have a density of about 7g/cm^3 and to be a ...
3
votes
2answers
86 views

Is it plausible that Mars could have been one of Jupiter's natural satellites at one time?

Would more questions regarding the planet be answered if this was the case?
2
votes
1answer
48 views

Divide a star catalogue to optimize star search

I'm continue working on my Planetarium software and I have a doubt. At this moment my star catalogue is very small, but I'm planning to use a bigger one. To optimize the search inside this catalogue ...
5
votes
1answer
113 views

How small a star can provide Sun-level illumination to its planets?

...or how small can a solar system be, to sustain an Earth-like planet? Sun is not really small, and 1AU is pretty far when you look at orbital radii of exoplanets and size of their stars. How small ...
2
votes
1answer
29 views

Formation of a magnetosphere for gas giants / small stars

This question got me thinking about this. Jupiter has, and presumably super-Jupiters can have a strong magnetospheres. A solid metallic core and rotating material around the core, creates a magnetic ...
2
votes
1answer
52 views

Age of Occator Crater

Has any official information been published regarding the estimated age of the Occator crater on Ceres? I ran some quick searches but couldn't find anything putting a definitive (or even speculative) ...
5
votes
2answers
178 views

Is there any hard evidence that rogue planets exist?

A rogue planet (or a rogue anything, for that matter: a celestial body other than a star) is something that's drifting through space without being attached by gravity to any star. They're just out ...
11
votes
2answers
2k views

Is Earth unique in its fairly clear atmosphere?

So, we have surface pictures from two alien planets, Venus (captured by the Venera 13), and Mars (captured by the rover). Both of these pictures appear to be very dusty. For Venus we see strong ...
1
vote
1answer
112 views

How do we know which elements are in a galaxy spectra?

I know that each element has it's own distinct spectra (this is a good site that lists them: Periodic Table) but when looking at a spectra of a galaxy (or even a star) how do we match those elements ...
2
votes
2answers
168 views

Can we have a second moon?

This question sounds like silly and rather fantasy filled. But can our earth's gravity capture a sizable asteroid and make it rotate around our earth like our moon which become visible from ground. Is ...
8
votes
1answer
51 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 ...
1
vote
1answer
275 views

Why does Earth have more gravitational force than the Moon if I stand on it?

Perhaps this is a silly question but I am trying to understand Einstein's general theory of relativity. I would like to explain my question in more detail. The greater the mass of an object, the ...
2
votes
4answers
143 views

Notable differences if all stars would disappear except the Sun

I am not an astronomy expert, but as of today, all other stars than the Sun have little to no effect on life on Earth. So I was thinking, would there be any differences for the Earth at all if all ...
3
votes
1answer
62 views

Is the size and heat of a star important in the development of a solar system?

How do the size and heat of stars affect development of solar systems and what kinds of planets can develop? Is it possible to orbit supermassive stars? Furthermore, would star's unleashing violent ...
2
votes
1answer
45 views

What is Color Index?

I found this Wikipedia page on this property called color index. Unfortunately, I could not find a source that explains this property well. My interpretation is that color index is the brightness ...
3
votes
2answers
381 views

Equation to find distance between objective and eyepiece

I have a home made astronomical telescope with 100 cm objective lens and 5 cm eyepiece.when viewing an object in infinity the distance between eyepiece and objective is 105 cm. So how could I ...
5
votes
3answers
153 views

Visibility of human activity on the moon

In this video the host of Test Tube Plus states that you can go out a buy a laser, point it at the moon, and see the retroreflector left by the astronauts. When you point at the right spot you'll ...
5
votes
1answer
212 views

Can a gas moon exist?

Could a gaseous moon exist in the same way as a giant gas planet? All the moons in the solar system are rocky, or icy. Why shouldn't gas planets have gas moons?
1
vote
0answers
70 views

Why some stars appear to move differently when viewing device shakes

I was looking at Arcturus with a pair of binoculars, and noticed that when they vibrate due to my heartbeat, Arcturus seemed to move differently than the other dimmer stars. I started playing with ...
3
votes
1answer
108 views

Does the Sun orbit the Milky way in a (kind of) flat or inclined orbit or more of a sine wave? [duplicate]

I know it can't be a perfect ellipse or smooth orbit due to all the matter in every direction, and our Sun could be affected by a gravity assist of sorts if it passes close enough to another massive ...
2
votes
2answers
193 views

Precessing of the Earth

It's been known that the Earth's axial tilt varies from 22.5 to 24.5. Does this result in a wobbling while the value of the tilt varies about these two limits? If so, how does it affect the mechanics ...
2
votes
1answer
90 views

What were the challenges for the ancients to observe the orbit of the Moon (instead of Mars)?

Astrophysics can be said to have been founded by Johannes Kepler around the year 1600. He based his break-through science on data of the position of Mars in the sky and disproved the ancient ideas ...
2
votes
1answer
99 views

How well do planetary orbits fit with Johannes Kepler's in- & circumscribed Platonic solids?

In Mysterium Cosmographicum (1596) Johannes Kepler proposed that the relative distances between the orbits of the six ancient planets (six because heliocentrism had recently added Earth as one of the ...
4
votes
2answers
259 views

Can we compress any object to create black Holes?

In general, when a star runs out of nuclear fuel, gravity gets the upper hand and the material in the core is compressed even further and creates black holes. I am clear till here. Now the question ...
3
votes
1answer
173 views

Is a black hole heavier than the star from which it was created?

I did some googling around and couldn't get answer to a simple question of black hole mass compared to the star from which it was created. It is well known that giant stars burn very bright and ...
8
votes
3answers
245 views

How do we know that our galaxy is a spiral galaxy?

I know that our galaxy is spiral in shape, but I'm wondering how the scientists found out that our galaxy has a spiral shape. I don't think we can see the entire galaxy from telescopes on Earth, ...
1
vote
1answer
111 views

Where did everything come from?

Where did all the material and gas contained in our universe come from? If it was the size of a "coin," then it could not have contained all the matter that is in our universe today before the Big ...
3
votes
0answers
58 views

How bright can white dwarf stars glow as they accrue matter?

I realize this is kind of general as it would depend on the size of the white dwarf and the rate of accrual. The general idea I got thinking about is what would happen if a white dwarf star - lets ...
2
votes
1answer
85 views

How can the observable universe be so small if there are so many stars in it?

The observable universe has a radius of about 46.5 billion light years. That’s big but I just wonder how that can be big enough to fit in everything we know exists in the universe. There are hundreds ...
2
votes
1answer
51 views

What is the share of stars in total radiation input of Earth?

Earth gets its radiation input primarily from Sun, then from reflected sunlight from Moon, and stars. Among these, what is the share of stars (or sources outside solar system) to this total radiation ...
9
votes
1answer
162 views

Did a piece of Halley's comet strike the Earth 1,500 years ago?

A friend showed me an article saying that there's evidence that a piece of Halley's comet may have struck the earth about 1,500 years ago. Is anyone here aware of such evidence?
1
vote
4answers
199 views

Does time slow down because the universe is expanding at an accelerating rate?

If the universe is expanding at an accelerating rate, such that the galaxies' moving away from each other is accelerated, then time should also slow down. And when universe will accelerate to the ...

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