# All Questions

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### 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?
125 views

### How does Titan maintain the atmosphere

Titan which is smaller than mars has an atmosphere but mars is not able to maintain atmosphere. Even Luna doesn't have an atmosphere.
258 views

### How to detect emission lines in optical spectra?

Is there any handy module to detect emission lines in a spectrum like one we get from the Sloan Digital Sky Survey (SDSS)? You can see there are many emission lines like Ha,OI in the spectrum below. ...
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### 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. ...
244 views

### Do moons have moons?

Have we discovered any natural satellites of natural satellites of planets or dwarf planets? Even very small, or relatively short-lived - e.g. ringlets around Saturn's moons, some meteorites orbiting ...
895 views

### Jupiter FM - What are practical and inexpensive ways for the amateur detection of signals from Jupiter, especially of the transit of her moons?

What modifications to a standard AM/FM or shortwave radio are needed in order to be able to detect radio-wave signals emitted from Jupiter? Would it be possible to detect the transit of the major ...
404 views

### How can the 13.8 billion years old universe have a radius of 46 billion light years?

The universe is about 13.8 billion years old. Assume at the big-bang it starts from a small region and the maximum possible speed according Einstein is the speed of light how can the universe got a ...
164 views

### What is the ultimate fate of a cluster of galaxies?

We're fairly aware clusters of galaxies drift apart due to space expansion, which will drive them out of each other's cosmic event horizon eventually, leaving them separate, alone, each a single ...
251 views

### Why is the Moon receding from the Earth due to tides? Is this typical for other moons?

After reading the Q&A Is the moon moving further away from Earth and closer to the Sun? Why? about the tides transferring energy to the Moon and pushing it from Earth, I have a question: How is ...
202 views

### Will new stars stop forming at some point of time?

New stars keep forming in the universe thanks to all the nebulae. Now, we need Hydrogen to form stars and there would a time when all the hydrogen will get exhausted, and no more star formation will ...
1k views

### Why isn't Earth a perfect sphere? [closed]

In general, almost everyone describes Earth as an perfect sphere, but in reality it isn't a perfect sphere. Is there any specific reason why Earth is not perfect sphere ?
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### What azimuth description systems are in use?

For a time, I thought Azimuth is always direction in degrees, 0 for local, geographic north, 90 for east etc. Then, trying to observe moonrise I downloaded an app that gave azimuth in values between ...
285 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 : ...
221 views

### How are Galaxy Super Clusters Generated

I have seen pictures of clusters of galaxies, usually used in regards to theories of dark matter and galaxy formations. One of the most famous ones has the perceived shape of a stick-figure. If I am ...
206 views

### Calculate Distance To Stars

I was just watching a lecture from Carl Sagan. He talked about figuring out the distance to the stars; it got me interested in learning more about the subject. As far as I know, the Inverse square ...
178 views

### How Does a Refractor Telescope Work?

As I understand it, the difference between a reflector and a refractor is that a reflector uses mirrors on the back to reflect the light to the secondary mirror then the secondary mirror reflects the ...
104 views

### What is the predominant element in the dust of the Sombrero Galaxy?

The Sombrero Galaxy contains a rather peculiar ring of dust orbiting it (seen as the dark ring on the outer edge). What is the prevalent element in this dust? Carbon?
171 views

### What is the object in this photo?

What object is in this photo? View coordinates: $47.25103 \ \ 38.81697$ Time: $2013$-$11$-$23 ~21$:$00 +4 ~UTC$ Sony $A580, \ 50mm f/1.4 15"$
181 views

### What happens to a star after it has become a red giant?

When our sun reaches the end of its lifetime , it will turn into a red giant. How long will it be a red giant, and what happens after a star has been a red giant? Does it turn into a planet after a ...
153 views

### What is the current accepted theory for the fate of hot Jupiters?

It is well established that one main feature of many hot jupiters is their close proximity to their parent star, usually the equivalent of being within the orbit of Mercury. So, these planets are gas ...
114 views

### Navigation using moon phases

How to navigate with possible maximal precision using moon phases? The Moon is the brightest celestial body seen in the night sky, and it is possible to find even through moderate clouds. So it's a ...
134 views

### Might Oort cloud comets be exchanged between solar systems?

Considering their distance from their parent stars, might Oort cloud object such as comets be exchanged between passing stars (assuming that other stars have similar Oort clouds)?
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### How many sun-like stars are there in the universe?

After yesterday's announcement of the Kepler telescope finding a huge amount of newly observed exoplanets, i saw a headline claiming that as much as 22% of sun like stars in the universe have planets ...
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### How do stellar temperatures vary?

The temperature of the surface of the Sun (photosphere) is between 4500° - 6000° Kelvin. Inside the core, it's around 15.7 million degrees Kelvin. In other types of stars (neutron stars, white ...
148 views

### Where is all the antimatter?

The universe supposedly started off with equal parts matter and antimatter and they are said to annihilate each other. Also, nature is famous for it's balance between everything. So all we see is ...
75 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 ...
108 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 ...
310 views

### Determining effect of small variable force on planetary perihelion precession

Is there an analytical technique for determining the effect of a small variable transverse acceleration upon the rate of aspides precession (strictly not a precession but rotation of the line of ...
94 views

### Is the surface of TrES-2b actually dark?

The exoplanet TrES-2b is known as the darkest planet ever found, reflecting <1% of the light that hits it. What does it mean in respect to the surface? What would we see below the atmosphere of ...
719 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 ...
377 views

### What was the length of year 1 million years back?

We know that the universe is gradually expanding and this indirectly means that the gravitational force between sun, earth, planets and other stars (roughly anything in the universe) is gradually ...
154 views

### Why is the interstellar medium so hot?

On this link, it states the following: "large assemblies of galaxies that are permeated by even larger amounts of diffuse gas. With temperatures of 10 million degrees or more". How are these ...
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### By putting a mirror in space, would we be able to see into the past?

I only ask this because of how fast light travels. The question remains in the title. Why, or why not, would this work?
317 views

### Layout of the universe

I've been working on a space game in my spare time, and lately I've been thinking on how to layout the universe. Though I searched around and found it hard to get a good view of what the universe ...
127 views

### Moon orbits crossing each other

Some planets, such as Mars, have 2 or more moons. Giants, like Jupiter of Saturn have a lot of moons! How likely the orbit of one crosses another one's orbit? Is it possible for two moons to collide? ...
348 views

### How do we know the big bang didn't happen in an existing universe?

I understand the evidence for the big bang (expansion, background radiation, etc), but how do we know that it was the start of the universe? Why couldn't it have occurred in an existing, but very ...
419 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 ...
233 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 ...
184 views

### How are black holes doors to other universes?

I'm watching MIT OpenCourseWare lectures on general relativity and not too long into the first lecture the professor stated that the Kerr Black Hole solution allowed for travel between universes. How ...
403 views

### Why can you see the space station on some days but not on others?

In my area, from December 17th - 26th, you can see the space station every day, twice But from December 27th - January 6th, you can only see it twice My question is, why does it appear for ...
269 views

### Why is the observable Universe larger than its age would suggest?

The age of the Universe is estimated at 13.8 billion years, and current theory states nothing can exceed the speed of light, which can lead to the incorrect conclusion that the universe can't have a ...
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### Why is the Earth's center still hot after millions of years? [closed]

Why didn't the center of the earth cool after millions or billions of years? What keeps it hot?
664 views

### What causes the dimensions of a star increase when its hydrogen fuel is exhausted?

What causes the dimensions of a star increase when its hydrogen fuel is exhausted? For example, the Sun is expected to increase its radius 250 times. What causes this if its temperature is expected to ...
805 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 ...
109 views

### Appearance (frequency) ranking of stars?

Is there some ranking / statistics that shows how common given type of celestial objects is? A table that would allow the answers to questions like: What type of star is most common per volume of our ...
199 views

### How old is our Sun in Galactic years?

A year is measured as the amount of time it takes Earth to orbit the Sun once, a Galactic year is the time it takes our sun to make one full orbit of the center of the Galaxy. In Galactic years, how ...
104 views

### Age of the universe

We know that the universe is approximately 13.7 billion years old. What methods did we use to discover this? How sure are we about its accuracy?
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### Why all the photos from 67p are black and white?

I was wondering why every picture we saw on internet about Rosetta's landing on 67p just black and white ? Is there something i should know ?