The science dealing with objects and phenomena located beyond Earth. In particular, this applies to observations and data. At its core, astronomy is the physically informed cataloging and classifying of the contents of the universe in order to better understand what is out there.

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Novice interested in buying a used telescope. What questions should I ask? [closed]

I've noticed quite a few decent telescopes for great prices on craigslist, but I am a complete novice and don't know the first thing about them. I thought I would be able to pick up what I needed from ...
12
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2answers
16k views

Is the moon a planet?

Can our moon qualify as a planet? With regard or without regard to the exact definition of the planet, can the moon be considered as planet as Mercury, Venus and Earth etc. not as the satellite of the ...
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2answers
93 views

Which direction before dawn to look for Comet Lovejoy (C/2011 W3)? [closed]

Various websites today are reporting with photos and videos of Comet Lovejoy. However, I can't seem to find a definition of which direction to look for it tomorrow morning. I'm in Christchurch, New ...
5
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1answer
87 views

Is there an established standard for naming exoplanets?

I understand that exoplanets are named by adding a lowercase letter to the a designation of the planet's parent star or stellar system, beginning with 'b' (the star itself is 'a') in order of ...
5
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1answer
68 views

Best observing techniques for a Total Lunar Eclipse?

Is there any good tricks to observing a total lunar eclipse that I should be aware of? Just wanting to know what to do to be prepared for the upcoming one, but please post in general for future ...
10
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1answer
565 views

How to explain the Moon halo phenomenon?

Today, here in Brazil, I have observed (and is still observing) an interesting phenomenon. The Moon is near to a big star in the sky, but this is normal. The interesting part is what's around them. ...
5
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2answers
682 views

How is the Hanbury-Brown and Twiss effect used to measure the size of stars?

I understand what an Hanbury Brown and Twiss (HBT) interferometer does, but how can this be used to measure the apparent angular diameter of some object? What is the mathematical explaination?
2
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1answer
148 views

Gravitational sphere

I was reading this article that mentions a blackhole as having a gravitational sphere of 4,000 light-years. I'd not heard of the term (gravitational sphere) before ...
6
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2answers
103 views

Is there any chance we could eventually observe the supernova of the first (Population III) stars

In an answer to my previous question about the first stars it was stated they probably formed at Z=20 to Z=60 and may have had a mass between tens to 100s to 1000s of times the mass of the Sun. Given ...
17
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10answers
317 views

In astronomy what phenomena have theory predicted before observations?

As far as I know, astronomy is generally an observational science. We see something and then try to explain why it is happening. The one exception that I know of is black holes: first it was thought ...
14
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4answers
2k views

Is there a limit to the resolving power of a mirror telescope?

Like, if you hammered out the asteroid 16 Psyche into a 1 mm thick iron foil disc telescope mirror with 2.4x the radius of the Sun, could you resolve details on the surface of an exoplanet? At what ...
7
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1answer
88 views

How are exoplanets confirmed?

In reference to the Kepler 22b news: The Kepler team had to wait for three passes of the planet before upping its status from "candidate" to "confirmed". This is possible because the planet ...
6
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2answers
128 views

Why doesn't a close comet like Elenin look like other, famous comets (Hale Bopp, Halley…), which have nice, long trails?

Elenin is a comet that runs very close to the Earth (0.8 times the Earth-Moon separation at its closest point). By naked-eye observation, it doesn't look like the other famous comets (Hale Bopp, ...
3
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2answers
333 views

The Bahtinov focusing mask

I'm looking for a webpage or a book or reference that might give me a better (and hopefully more scientific) understanding of how the Bahtinov mask works (which I understand to be the same as ...
3
votes
3answers
61 views

November 25th 2011 partial solar eclipse visibility from Christchurch, New Zealand

Where can I find a site that will give me an indication of coverage for the November 25th 2011 partial solar eclipse as viewed from Christchurch, New Zealand tonight, as well as local times for the ...
6
votes
1answer
94 views

Detecting dim objects

What are the minimum conditions (switching times, sensitivity ...) for a camera to detect dim objects, e.g. Oort cloud or Kuiper belt objects, passing by in front of a star in the background? I've ...
6
votes
1answer
132 views

Is the Apophis asteroid a concern?

I was watching the TED lecture How to defend Earth from asteroids , and the speaker Phil Plait spoke of the possibility of this asteroid hitting Earth. He also said something about a Mayan legend. He ...
6
votes
1answer
33 views

Liquid Water in “mid-ice” on Europa. Mechanism?

Recently I read this entry by Dr. Phil Plait (a.k.a. The Bad Astronomer). He is talking about a lake of water contained within the ice layer of Europa. the lake is completely embedded in the ice ...
1
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1answer
536 views

Calculating position using shadows

Suppose, we know the length of the shadow of an object at some known time. Can we use the this information to find position of the object (the longitude )?
5
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1answer
90 views

Shadow of a Jovian moon over the Great Red Spot

Where can I find pictures of the shadow of any of the Jovian moons partially covering the Great Red Spot? A series of such pictures over time would even be better. The idea is to learn more about the ...
2
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2answers
148 views

Best time of the year to see the star Alpha Centauri in Chile, Santiago

If I'm in Chile, Santiago, what is the best time of the year to see the star Alpha Centauri at the beginning of the night?
0
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1answer
62 views

Is it possible to check from the EM waves(basically Light rays)?

Is it possible to check from the EM waves(basically Light rays), if there are any extraterrestrial objects interference/passage during its travel from the Sun? I mean, can these EMs from the Sun be ...
10
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2answers
250 views

Why did population III stars lack planets?

Jay Wacker1 (professor of physics at the SLAC National Accelerator Laboratory) stated: The first stars (known as Pop III) were made out of hydrogen and helium. They had no planets. Why couldn't ...
2
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2answers
226 views

How do I find the time for Pleiades to be at Zenith today

I am looking for a way find the time when: Pleiades will be at the Zenith today (11th November 2011) Pleiades will conjunct with the Moon The Moon will be at the Zenith today How do I find those ...
4
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3answers
2k views

Use of advanced mathematics in astronomy, like topology, abstract algebra, or others

I know that topology, abstract algebra, K-theory, Riemannian geometry and others, can be used in physics. Are some of these areas used in astronomy, and are some astronomical theories based on them? ...
9
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2answers
524 views

Where does the dust on the moon come from?

From the Apollo missions we know that the moon is covered with dust. Where does it come from? Is it from the erosion of the moon rock? By what? Or by accretion of dust from space? Which comes from ...
6
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1answer
61 views

Transit of Mercury: how did he see it?

On November 7, 1631 Pierre Gassendi saw the transit of Mercury across the face of the Sun. How did he see it? I mean what instrument was used to reduce the apparent brightness of the Sun?
2
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1answer
20 views

Are there trends in the number of meteors in a shower year on year?

Some years the Leonids are amazing, other years there are very few - are these predictable at all, following trends or at least reasonably accurate predictions?
2
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3answers
43 views

Where can I find a list of when I can see something in the sky?

My son is very keen on Astronomy but I don't know when there are meteor showers or something else that would be worth going out to the country to see. Last year we went to see a meteor shower, but I ...
4
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2answers
40 views

How bright will an asteroid be?

In the news, it has been stated that there will be a fairly large asteroid passing fairly close to Earth soon. I've been trying to find a good observation guide, including determining how bright it ...
7
votes
1answer
109 views

What's the most accepted theory for Blue Stragglers These Days?

I'm working on a post against a recent creationism article about blue stragglers. From when I was in undergrad, the general explanation was that they were likely second generation stars within ...
1
vote
2answers
990 views

What is a good introductory text to astronomy [closed]

What is a good and easy to read introductory text for an adult with limited basic scientific knowledge to astronomy for someone without a telescope and lives in a big city and why do you think that ...
5
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2answers
62 views

Does Mercury have a balmy spot?

From Wikipedia: Although the daylight temperature at the surface of Mercury is generally extremely high, observations strongly suggest that ice exists on Mercury. Does that mean there could be a ...
11
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3answers
1k views

Why is this radio telescope's reflector spherical and not parabolic?

This is the Arecibo Observatory in Arecibo, Puerto Rico. Its reflector is spherical, measuring 1,001 ft. in diameter. It is considered the most sensitive radio telescope on Earth, but the fact that ...
4
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1answer
228 views

Why isn't sunset time in sync with solstice?

The winter solstice in the Northern Hemisphere in 2011 is on December 22. But if I look at the sunset times for a location such as Washington, DC on the USNO site, the sunset time starts reversing ...
2
votes
1answer
144 views

Get time from sun Azimuth

I want to know if I can determine the time where the sun's azimuth is at a given value. In other words, I want a function that takes the sun azimuth along with longitude or time zone and outputs the ...
16
votes
1answer
5k views

Which way do spiral galaxies rotate?

Is it known whether spiral galaxies typically (or exclusively?) rotate with the arms trailing or facing? Intuitively it feels weird to think of the arms as facing the direction of rotation, but that'...
10
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2answers
342 views

How fast is the Cosmic Microwave Background Radiation (CMBR) changing?

I know that the Cosmic Microwave Background Radiation (CMBR) is the leftover radiation from the "surface of last scattering". However, at every instant the surface is changing (at the rate of flow ...
3
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0answers
187 views

Parallax Cloud Displacement - Angular Distance from Geostationary Satellite

When observing clouds from a geostationary satellite, they appear displaced because of the parallax effect. The satellite looks at the clouds "at an angle" and it projects them on a point of the earth ...
4
votes
1answer
113 views

How is the atmosphere composition of astronomical objects in solar system determined?

How is the atmosphere composition of astronomical objects, for example triton, the moon of neptune, determined?
2
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2answers
4k views

How much of sky can be seen on a typical night from a mid-latitude location?

I'm at about 40deg north so, assuming a clear southern horizon, I can't see things below about -30 or so (I actually don't know how far south). I also have a large portion that is circumpolar so it's ...
3
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1answer
78 views

What could this very dark planet be made of?

I was reading about the planet TrES-2b which is less reflective than charcoal. What could possibly be its composition?
4
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3answers
529 views

Pleiades through a 15x 76 mm telescope

How clearly can the stars of the Pleiades cluster be seen through a 15x telescope (for example, FunScope)?
7
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1answer
2k views

What are the minimum telescope requirements to view a nice spiral galaxy?

I would like to view some spiral galaxy. However, I would prefer not to spend lots of $$$. What are the minimum specs a telescope must have to resolve detail in a spiral galaxy?
3
votes
3answers
284 views

Name for celestial “Prime Meridian”?

Is there name for the line that goes from celestial pole to pole at RA 0 degrees 0 minutes 0 seconds? On Earth we would call it the Prime Meridian. Is it called the "Celestial Meridian"?
4
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2answers
3k views

Density of stars near the center of the Milky Way

At night, I can look up and see the Milky Way across the sky. My question is, supposing our solar system was, instead of way out on an 'arm' of the galaxy, if we were near the galactic center. Would ...
14
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5answers
4k views

Telescope for 6 year old and dad new to astronomy

What's a good telescope for my 6 year old? We're both brand new to telescopes in general, but love space, stars, planets, cosmology, etc. Happy to spend up to $200 to start. Maybe more for a good ...
6
votes
1answer
1k views

Is there a simple yet accurate formula for where on Earth the Sun and Moon are directly overhead?

I'm trying to improve a site that shows the region of the Earth currently under daylight, and I need a formula that, given the current time, tells where (latitude/longitude) the sun and moon are ...
5
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2answers
99 views

Tropical year is 27s/year off from Gregorian year?

http://hpiers.obspm.fr/eop-pc/models/constants.html states the tropical year is $365.242190402$ days. The Gregorian calendar's average year is $365.2425$ days (every 4th year a leap year, except ...
4
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1answer
27 views

What demonstrations for a five-hour optical and radio astronomy workshop? [closed]

I volunteer at a group that has restored the oldest German radio telescope. We are now at a point where we want to invite interested amateur astronomers and school children to workshops. I'm currently ...