# All Questions

2k views

### Why doesn't Earth's axis change during the year?

My understanding is that the Earth's axis points in the same direction in space during its entire orbit around the sun. And this is what causes our seasons. My question is why doesn't the axis follow ...
81 views

### landing on a comet is more important than landing on an asteroid?

Philae landed on comet 67P this year. And it means a big breakthrough for the science and technology of human being. However Hayabusa mission of Japan not only landed on an asteroid but also returned ...
459 views

### Are there any known objects in a “dual” tidally locked orbit?

Is there any known pair of objects tidally locked with each other? I know the moon is tidally locked with the earth (e.g. one side always facing earth), but I don't know of any pair of objects that ...
484 views

### Position of Neutron stars in H R diagram

Why is that Neutron Stars are never depicted in an H R diagram? They can be placed in the bottom right corner but you will never find any diagram in literature showing neutron stars.
108 views

### How should exoplanet discoveries affect SETI?

Given that SETI was created before the discovery of exoplanets, has this changed how they search? Would it make more sense to focus efforts on discovered earth like exoplanets?
100 views

### How to read 5 degree data of green line intensity

When I open the 5 degree data of Green Coronal Emission line from this, I get a weird table which is not simple like the one for Coronal Index. I am only providing the table for 1939. ...
114 views

### How do I get from Star Atlas to real life?

This question is about finding the elevation and bearing of a given star at a particular time at Latitude 52N. I look up the RA and Declination of my star. How do I calculate its bearing and ...
331 views

### What is the temperature of an accretion disc surrounding a supermassive black hole?

What is the temperature of an accretion disc surrounding a supermassive black hole? Is there plasma in the disc?
165 views

### How is the diameter of a gas giant calculated?

As we know atmospheres of celestial bodies don't just stop at a given distance. They gradually become less dense as you move away from the center. I understand that the diameter of stars is ...
56 views

### Which wavelength is the most quiet, for a ground-based radio telescope?

This might seem like a backwards question, but I'm interested in what wavelength to select in a (hypothetical) ground-based radio telescope observation to expect detecting as little as possible! :) ...
72 views

### One Universe or Multiverse? [closed]

I watched a program where four astrophysicists were debating this topic. I couldn't fully understand what they were saying but wanted to ask others' opinions on whether there is only one Universe or ...
248 views

### How to see Saturn's rings through a pair of binoculars?

I have a pair of 15x70 binoculars. I would not say what manufacturer to avoid being the subject of 'hold'. The current angular diameter is 15.5 arcseconds. I am wondering if that condition is enough ...
101 views

### What are the odds of (Semi) Intelligent Life in the Milky Way? [closed]

I know that it can vary A LOT if you are using the Drake Equation but using realistic figures, how likely is it to discover a civilisation that is at least semi-intelligent (stone age - medieval era, ...
257 views

### Is it possible for a star to orbit a planet?

Is it possible for a red dwarf to orbit a gas giant? OR Has this happened and it is just assumed that the gas giant is orbiting the star?
315 views

### Cancelling out earth rotation speed, Altazimuth mount

I have a Dobsonian telescope. It is using Altazimuth mount. Basic idea of using it is to target the object by moving telescope vertical axis perpendicular to the ground, and an elevation axis that ...
119 views

### Universe as 2d sphere surface - a round trip?

If Universe's analogy is 2D surface of the sphere, could we come around in circle? Say on Earth you decided to travel straight in one direction, after completing one full circle you'd find yourself at ...
225 views

### Basic DIY Telescope

I am looking for a design of a cheap and easy telescope to build with my 9yo daughter with the only basic requirement being that I'd love to be able to see detail on the moon. Looking around, there ...
75 views

### How can I make Stellarium match the magnitude of stars visible in London, UK?

Can someone recommend some Stellarium settings to mimic the amount of light pollution, and magnitude of stars that should be visible on a clear night in London, UK?
339 views

### Full Moon Position of Sun

I am trying to figure out the position of sun with respect to moon on a full moon day. Here's an image from certain wiki which I do not find convincing. 1 If the sun rays point as shown in the image ...
95 views

### Why do comets come from our local Oort cloud instead of from interstellar sources?

Comets form where stars form. And they are then ejected by the orbital changes of giant planets. But why are they ejected to form specifically a local Oort cloud instead of going interstellar and ...
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### Why is a star at its highest point when local sidereal time = RA (right ascension)?

I'm currently taking a course called Introduction to Astronomy at Coursera. It's not very formal so they didn't present a proof of the statement in the title. I understand why logically one could ...
35 views

### Is Nomad data heliocentric or geocentric?

I'm wondering if the data in star catalogues are heliocentric equatorial coordinates or geocentric equatorial coordinates. Also given the distance between stars compared to the distance between the ...
86 views

### The multiverse spacetime paradox?

If there are indeed multiple universes, where do they exist? We "know" that outside our universe, consisted of spacetime, there is nothing - i.e. 0 dimensions, no space and no time. So "where" are ...
61 views

### How do we know an event is a gamma-ray burst?

How do we know an event is a gamma-ray burst (grb)? There are two kinds of grbs, long burst and shot burst, which are caused by supernova explosions explosion and the merger of two neutron stars, ...
41 views

### How do we get radio signals of the big bang?

From TV shows I have known that we still get some radio signals of the big bang and they are every where. My question is is the universe expanding so fast that even electromagnetic wave has failed to ...
139 views

### What is a possible software for simulating binary star systems?

I would like to define both initial velocities and masses of components so that orbits may be either elliptical of hyperbolic. Is there any software to make such simulation? Unfortunately, Binary ...
213 views

### Would Pluto keep an orbit without its moon?

I haven't studied space that much, but I know that Pluto has very little gravity, but just enough to keep a human on its surface. Would Pluto keep a regular orbit around the sun without some extra ...
101 views

### Photos from galaxy

So, I hear people say blah blah blah is 3 light years away, and here's a photo. So does that mean the photo that we see are actually at least 3 years ago since that's how long it takes that light to ...
44 views

### What is the boundary in the atmosphere seen in this video?

This video, which shows time-lapse views of Earth from the ISS, consistently shows some sort of hard boundary in the atmosphere, below which there seems to be significant reflection from sunlight ...
164 views

### The role of gravity during planetesimal accretion

As far as I understand, during the formation of a planetary disc, grains of dust stick together due to collisions and chemical bonding. Considering the size of the grain - say, 1 mm - and the speed - ...
644 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.
320 views

### Can A Black Hole Exist?

In 1939, Robert Oppenheimer and other concluded that a certain neutron stars could collapse to black holes and no known law of physics would intervene. As far as I can tell, there is no observational ...
50 views

### What is the Habitable zone all about?

I've a question on Habitable zone. Does Habitable zone represent the region where we humans or the living beings of earth can survive? Or is it a region where life can exist? If it is second I want ...
61 views

### Why dont we have a browsable spacetime augmented virtual solar system?

Wouldnt it be nice to be able to render any viewpoint from all the data transformed into a point cloud, an augmented virtual reality of moving objects in our solar system. I would just like to be ...
85 views

### Gravitational tidal force problem

if we have spherical mass held by its self-gravity, there will be a limit to distance - let's say it is $r$ - that the center of this body may approach a much more massive body (lets we call $M$ ...
433 views

### What to look for in a tripod for binoculars?

I have been looking at large astronomy binoculars in the 25x100 and 20x80 range. Clearly, these monsters cannot be held steady by hand, or even be held at all for any reasonable length of time using ...
113 views

### Limit of hotness!

We know that there is a limit to which an object can be cooled down that is absolute zero, and getting there is also not very easy we may have to wait infinite years to get to that point. But is there ...
89 views

### Is CMB Polarization simply the temperature gradient of the CMB?

Firstly, I have to admit that I don't fully comprehend the concept of "CMB Polarization". When I think of "Polarization", I normally think of the optical definition of polarization, as defined by the ...
593 views

### What is the exact mass of the Sun?

I am having trouble finding data on this. So far, I have found at least seven values: ...
456 views

### Are the stars in constellation located in a plane or they are in different distances

Are the stars in constellation located in a plane or they are in different distances from each other and when we observe them from the Earth we think they are all in a plane?
209 views

### Can Jupiter's bands be made out using a 15x70 pair of binoculars? [closed]

I have been getting mixed opinions on this. I have a 15x70 Pair of Binoculars. I have tried staring at Jupiter for several minutes with it, I was able to see the Galilean moons, in fact the last time ...
112 views

### Smallest body that can be observed from Earth?

What is the minimum size of an object that can be observed from Earth with our most powerful telescope? I understand that the answer depends on how far the object is from Earth. For the sake of ...
3k views

### Does the Earth have another moon?

I was just wondering what are the chances that there is a small object (say less than 1 km but more than few meters) that orbits the Earth but has remained undetected by us? Are we actually ...
355 views

### Look up current positions and velocities of solar system objects

I am working on an orbital dynamics code and, for fun, I would like to model the Sun-Earth-Moon system with my code. I can look up the masses of each object just fine, as well as average distances ...
241 views

### Is there anywhere I can find some kind of database on all known stars and their properties (mass, surface temperature, radius, and luminosity)?

I have been looking for some kind of collection of all known stars and their individual respective mass/radius/temperature/and luminosity, can you link me to one if it exists? My goal is to write an ...
295 views

### What is the orbit of Earth around the Sun?

According to wikipedia and other sources, a planet and a star always move in a circular orbit around the common center of mass of the both bodies, in case of Earth and sun, this center of mass lies ...
98 views

### What determines the configuration of orbits in a binary system?

There are essentially two configurations of orbits a system with two bodies can have: A configuration where the paths do not cross: A configuation where the paths cross: Note: Size of the ...
86 views

### How would vehicles travel through the interstellar medium with its such low density?

I've heard from a number of different places that the density in the interstellar medium can have an average of 1 atom per centimeter cubed. Perhaps I have a wrong understanding of what 'nothing' is ...