# All Questions

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### Line of lights moving in a straight line, with a few following

My husband and I have just seen a line of about 15 lights moving in a straight line, quite high above the cloud level with a gap, and then 5 lights, a gap, another few, a gap, 1 light, a gap, and a ...
243k views

### Star like light moving in the sky, what could it be? [closed]

I was camping this weekend away from the city, so my friends and I decided to spend one of the nights watching the sky, since it's impossible to see anything around where we live. After a little while,...
4k views

### Where can I find the positions of the planets, stars, moons, artificial satellites, etc. and visualize them?

What resources are available to find the positions of planets, stars, moons, artificial satellites, asteroids, and other heavenly bodies?
8k views

### What is in the center of the universe?

If the universe has formed & originated by a Big Bang Explosion, then there must be empty space left in the center of the explosion site, as all the matter is travelling at tremendous speeds away ...
10k views

### How can the universe be infinite?

I've heard from renowned astrophysicists that we don't yet know whether or not the Universe is infinite. How is that possible regarding the big bang theory is accepted (as they all do)? Are they ...
15k views

### How can there be 1,000 stellar ancestors before our Sun?

I've heard from a few sources* recently that the Sun is a 1,000th generation star, meaning it had a thousand stars that came before it based on its heavy-element content. I understand that earlier ...
13k views

### Why is only one side of the Moon visible from Earth?

Why do we only ever see the same side of the moon? If this is to do with gravity are there any variables which mean we might one day see more than we have before?
9k views

### Does matter accumulate just outside the event horizon of a black hole?

My understanding is that time slows and approaches stopping when approaching the event horizon of a black hole. I have seen this explained several places, including a brief explanation in the last ...
3k views

### Will we start seeing galaxies disappear due to Universe expansion? [duplicate]

Does the fact that universe is currently expanding at an accelerating rate means that far far away objects (FAO) might start disappearing with time, set aside the "red shift"? I'm saying this ...
4k views

### how far away could we detect that Earth has life?

My guess is that life bearing planets are too far apart to be detected. I think we can only find the ones within a sphere around our planet that is 100s of light years in diameter but I suspect life ...
1k views

### Are there any galaxies which fell out of sight horizon due to cosmic expansion?

If farthest galaxies run away from us with acceleration making them exceed speed of light, we should expect them to disappear from sky among time with increasing quantity. Did we observe this? Can we ...
4k views

### What is a singularity? What is at the center of a black hole? Specifically regarding space-time

So because I can only really think of space-time in 2-dimensions like a sheet of something, my assumptions might be wrong to begin with. I was watching a YouTube video on black-holes and there was a ...
14k views

### How far is the Earth/Sun above/below the galactic plane, and is it heading toward/away from it?

How far is the Earth/Sun above/below the galactic plane, and is it heading toward/away from it? We know the Sun is orbiting the galactic center every 225 million years. But how far are we from the ...
3k views

### Is it possible that the Sun has a binary partner (the Nemesis Theory) that has eluded detection? [duplicate]

I just recently learned about the theory that our Sun has a small companion star with a 26 million year orbit. This theory came about when it was realized that mass extinction events happened ...
476 views

### Do astronomers generally agree that the distinction between comets and asteroids is not so clear?

edit: I just saw this tweet and find it incredibly relevant :) begin question: See this answer and then consider if there are known or likely solar system bodies that might be identified as both ...
7k views

### Why hasn't the "9th Planet" been detected already?

In the comments to this question, there was considerable doubt placed as to the subject of if the so called "9th planet" really exists. That wasn't really the intent of the previous question, so I ask ...
7k views

### Is the influence of gravity instantaneous?

When I was in college, I posed to my astronomy professor a thought experiment that had been puzzling my mind for some time: "If all the matter in the Sun magically disappeared instantly, how long ...
4k views

### Do we know the exact spot where big bang took place?

If you rewind the universe back 14,7 billion years, all matter were in one spot, and then started expanding. Do we know where this is in reference to our own solar system? And is there anything there? ...
3k views

### Need Simple equation for Rise, Transit, and Set time

I've been looking, unsuccessfully, for hours for a simple set of equations: Input: RA and Dec of an object Observers Lat and Lng Current Time Output: Rise Time Transit Time Set Time (and, ...
8k 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 ...
4k views

To the extent of my understanding, Olber’s paradox states that if the universe was static and homogeneous, we should see a star at every point in the night sky and therefore the night sky should be ...
691 views

The question Why is this video showing radio waves transmitted from a radio telescope? and this answer to it got me thinking. If atmospheric seeing at visible wavelengths is the result of refractive ...
4k 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 ...
2k views

### Why does a planet rotate and revolve?

Why do planets rotate and revolve in the universe?
511 views

### How does the Event Horizon Telescope implement the interferometry?

The BBC article Event Horizon Telescope ready to image black hole describes the Event Horizon Telescope, a coordinated observing technique with several radio telescope arrays across the globe forming ...
800 views

### What will it finally take to accurately measure the distance to Betelgeuse?

Comments below What is the maximum distance measurable with parallax? discuss challenges associated with parallax measurements of Betelgeuse and link to Wikipedia’s Betelgeuse; Distance measurements ...
516 views

### Why aren't ground-based observatories using adaptive optics for visible wavelengths?

Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing. The atmospheric effects are quite ...
349 views

### What is the highest granularity focal-plane array on a dish radio telescope? Or is this the ONLY ONE?

There is a short Wikipedia article Focal Plane Arrays that enumerates some projects, but my question is more along the lines of what is (at least) nearly complete or in "first light" phase, even if ...
3k 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 ...
20k views

### A good telescope for the viewing of Nebulae, Stars and Planets

So, I am a 15 year old interested in astronomy. My father used to have a reflector telescope, but was never so serious about it that he could recommend me a good telescope. I am looking to buy a ...
2k views

### If Alpha Centauri A's solar system exactly mirrored our own, what would we be able to detect?

Suppose there was an exact replica of our solar system 4.4 ly away (people included). What would we be able to detect and with what telescope(s)? Which planets? Could we detect radio transmissions and/...
2k views

### What are the main differences between solar flares and coronal mass ejections?

Specifically, what causes them, what sort of damage can they cause, and what are the differences in their composition?
3k views

### What is the current accepted theory as to why Venus has a slow retrograde rotation?

According to this NASA overview, the planet Venus is unique (amongst the major planets), Venus has a slow retrograde axial rotation, taking 243 Earth days to make one rotation (which is longer than ...
7k views

### Is Sun a part of a binary system?

Does our Sun have a counterpart, i.e., is it a part of a binary-system? If so, how does the other star look like and where is it?
2k 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 is ...
788 views

### Are there ways to estimate size of the "whole universe"?

Words escape me, but by "whole universe" (I think) I mean everything that's spatially connected to the observable universe in a conventional sense. If there is a better term for it, please let me know!...
3k views

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

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 ...
9k views

### Why do the planets in our solar system orbit in the same plane?

(Yes I'm excluding Pluto from this the same way it was excluded for not being a planet) Observing the planets orbit of the Sun they all seem relatively planar and roughly all orbit along the same ...
14k views

### Why do (most of) the planets rotate counterclockwise, i.e. the same way the Sun does?

Referring to the mechanisms explaining the solar system formation and to the initial rotation of the gaseous cloud that collapsed, I understand easily why the planets orbit the Sun the same way this ...
145k views

### How much magnification is needed to see the planets of solar system?

I have a 3inch Newtonian reflector telescope with 300 mm focal length. I can use highest magnification of 75x using a 4mm eyepiece. But in 75x I can't see the details of Jupiter what was expected. ...
3k views

### Will the Earth ever be tidally locked to the Moon?

From my basic understating, Momentum is being transfered from the Earth's rotation to the Moon's orbit by tidal friction. The Earth's rotation slows down and the Moon receedes from the Earth as it ...
1k views

### Is there enough hydrogen left after a star dies so another star will have enough to light up?

A star consumes quite a lot of hydrogen in its life, and is pretty much "vacuuming" everything in its vicinity. After it dies (eventually by supernova which will spread all its composition over light ...
7k views

### Local Sidereal Time

I am trying to understand how to calculate local sidereal time and have found the following formula: $$\text{LST} = 100.46 + 0.985647 \cdot d + \text{long} + 15 \cdot \text{UT}$$ Here, $d$ is the ...
104k views

### How long does a sunrise or sunset take?

From the time that the sun appears on the horizon, or meets it on its setting, to the time that it is fully visible, or no longer visible on its setting, how much time passes? Secondly, is there a ...
1k views

### How (the heck) does Astrometry.net work?

What magic is this? This answer to my question Astronomy detective question: what part of the sky are these photos of? What are a few of the stars? nails it, and the output (linked there) contains ...
1k views

### Is our universe included inside a black hole? [duplicate]

This question repetitively comes to my mind but I've never found any good scientist article to argue about it, only esoteric or speculative web articles without much valuable background. So let's ...
2k views

### How does the Moon move in the "night" sky as seen from the poles?

A photo in the NYTimes article Ice Surveys and Neckties at Dinner: Here’s Life at an Arctic Outpost has got me thinking. During the winter months at either the north or south pole, when it is ...
38k views

### How many planets are there in this solar system?

So, in school (that's a long time ago) they have been teaching us there are 9 planets in our solar system. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto But every now and then I keep ...