# All Questions

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### Metal rich or metal poor?

What does the image in the link mean? Are the stars in the halo high in metallicity or low? How about at the bottom by the disk? http://science.psu.edu/alert/images/SDSSmetals.jpg/...
146 views

### How do you calculate length of day in a multiple-star system?

How can you calculate the length of day for a planet (given a particular latitude and longitude on that planet) orbiting multiple stars? What about a planet that is orbiting one star, but that star ...
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### Is metallicity low at the central region or nucleus of the Milky Way?

Is metallicity low at the central region or nucleus of the Milky Way? Does metallicity decrease or increase as we move from the center out to the edges of our galaxy?
148 views

### Name and language of symbol in astronomy book

I've been working on a programming project involving Peter Duffett-Smith's Practical Astronomy With Your Calculator (3rd Ed.), which has a large number of mathematical/astronomical formulas in it. ...
61 views

### Age of the universe vs. its contents

A couple of decades ago I read an article (could have been either Astronomy, Space, or Science News) that suggested the contents of the universe may be older than the universe itself. Of course, that ...
46 views

### Does the universe prefer a velocity?

As I understand it, the distribution of matter is roughly homogeneous across space -- anywhere I stand in the universe, there will about the same amount of matter in every direction around me. Is the ...
35 views

### Available data on the Milky way around 1920

In a book by Alexander Moszkowski, there is an Einstein quote about a hypothetical size of the universe (100 million Light years). Moszkowski claims that Einstein had deduced that from the ...
37 views

### How can I use Polar Alignment to find objects in the sky?

I have a six inch telescope on an equatorial mount and I've been struggling to use the mount properly. For a couple months now, the only strategy I've used is just 'point and look.' I've watched some ...
512 views

### Does Sun have a reflection on Earth?

The new Google Maps1 presents an actual view of Earth, with the current position of Sun illuminating half part of Earth in real time. It is quite an exquisite view. My question is based on the ...
101 views

### What was the orbit of the meteor that impacted the Moon on 2013 September 11?

On 2013 September 11th, a meteor impacted the Moon leaving a 34-meter crater. So far the only info I've found was from youtube (https://www.youtube.com/watch?v=zCFDkj2JtyA) and this site: http://lroc....
55 views

### What is the force of a CME on objects in space?

I've been reading a little bit about coronal mass ejections lately and they seem really interesting, and they cause a lot of amazing things to happen. However, one thing I haven't seen is the physical ...
45 views

### How do we convert other waves of the EMS to visible light?

So I just had a quick question and I was wondering how we convert other waves of the electromagnetic spectrum to visible light waves. For example we use X-ray's or radio waves to see things in space ...
75 views

### Apollo Moon Landing [duplicate]

Can there be any truth to the rumour that the Apollo Moon landing in 1969 was staged ? I dismissed this rumour as being nonsense but today on the news I was surprised to hear that the head of the ...
356 views

### Is it possible to use Hubble Telescope to observe Earth in the past?

We can observe many astronomical objects and structures beyond our solar system, however our observations are as the objects appeared in the past due to the speed of light. My question: "Is it ...
99 views

### Question about total absolute magnitudes of galaxies - negative or not?

I have seen this in a couple of places, but when the authors in the paper - http://chandra.as.utexas.edu/~kormendy/kfcb-accepted.pdf - wrote: "All 10 of our ellipticals with total absolute ...
76 views

### Pulsars: How do astronomers measure minute changes in period (~picoseconds per year)?

I've been to some talks that mention how stable the period of a millisecond pulsar is over long periods of time. Recently, it was mentioned that astronomers have calculated the change in period over ...
71 views

### How accurate are rederings of something entering Earth's atmosphere?

Supposedly how accurate is it when you see a movies showing something entering Earth's atmosphere traveling 1 mile to 10 miles an hour or barely at all but skinning the atmosphere they show it heating ...
213 views

### How does the Grand Tack Hypothesis explain how Jupiter formed inside the frost line?

The Grand Tack Hypothesis states that Jupiter formed at roughly 3.5 AU from the Sun, then interacted with a large portion of objects in the Solar System before settling into its current orbit. Yet as ...
350 views

### How did Jupiter form where it is?

Since Jupiter is the biggest planet in our solar system and is made up of mostly hydrogen and helium, (the gases the Sun uses to create energy), how come it didn't form as far out as say Uranus or ...
222 views

### Why won't the Milky Way colliding with Andromeda affect the Solar System?

According to Wikipedia Such an event would have no adverse effect on the system and the chances of any sort of disturbance to the Sun or planets themselves may be remote. I'm imagining that this ...
554 views

### Why does the focal length of a telescope have an effect on the magnification?

I previously asked that Is the angular resolution of a telescope irrespective of used eye-piece? I learned that the resolution is fixed when the light enters the telescope, and that the eye-...
66 views

### Accelerating universe expansion and standard candle

Recent stars (and standard candle supernova), afaik, contain more heavy elements than older stars. As consequence, I guess, recent stars and supernova should be slightly dimmer than older stars? If ...
90 views

### What makes a really good observatory site, besides altitude?

Let's limit this to optical telescopes. I understand that the higher you are, the less atmosphere is above you to get in the way of observations. From reading around, there seem to be a few more but ...
80 views

### How do astronomers determine the texture of an exoplanet?

So I was wondering how astronomers are able to get the texture/detail of an exoplanet or how they know a planet has water or not. I know how they discover planets by using the light of a star and ...
577 views

### Moon's orbit around the Sun

The Earth revolves around the Sun and the Moon revolves around the Earth. Out of curiosity I started thinking about the orbit of the Moon around the Sun and expected (assumed) it to be as follows: ...
110 views

### Is the Universe really expanding at an increasing rate?

Here's what I just read from Wikipedia's page on the Hubble Space Telescope: While Hubble helped to refine estimates of the age of the universe, it also cast doubt on theories about its future. ...
63 views

### Is the Dwarf Planet class really necessary?

Another way of asking this is, what is the difference between dwarf planets and asteroids? Aren't they the same things? It's just that some asteroids are spherical and others aren't...or is there ...
123 views

### Is it accurate to compare comets to clouds and rain?

I'm trying to avoid an opinion-based question, so before I outline the comparison I'm proposing, I will qualify the specific facts that yield this comparison. By focusing answers on the relative ...
38 views

### Trouble understanding speed-dispersion in (elliptical) galaxies

I'm learning about LOSVDs (Line Of Sight Velocity Distributions) and I'm having a bit of trouble understanding the used terms. As I understand, the LOSVD of a given (elliptical) galaxy is the density ...
318 views

### What would be the practical consequences (on earth) if the Moon was not tidally locked?

I was thinking about the fact that all the largest Solar System moons are tidally locked to its primary and this question arose.
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### Is the angular resolution of a telescope irrespective of used eye-piece?

Suppose a telescope has aperture $D = 20$ cm. The angular resolution of such telescope, according to the Rayleigh criterion (if I have understood it correctly), is given by \theta = 1.22\cdot\frac{...
620 views

### I'm having trouble achieving sharp telescope focus

I've been having trouble getting really sharp focus on my telescope. Using Saturn as a reference, with a 20mm eye piece it is very sharp. But when I go to 10mm or 6mm, it gets bigger and blurrier. I ...
136 views

### Isn't the date of the Big Bang a bit bogus?

If I understand correctly, the date of the Big Bang is an extrapolation of acceleration of the universe's expansion through time based on the erroneous assumption that the universe is approximately 13 ...
34 views

### Do Noctilucent clouds cause problems with telescopes?

Noctilucent clouds are at around 85km altitude and are formed of ice crystals. The ISS recently posted a number of photographs of these clouds and pointed out the key feature, which is the bright blue ...
139 views

### Photometer vs. CCD-camera

The Wikipedia article on photometry says that These have largely been replaced with CCD cameras that can simultaneously image multiple objects, although photoelectric photometers are still used ...
47 views

### Calculating effective SSN (sunspot number)

I am doing research on SSN like parameters. As I can see effective SSN is a parameter that derived from SSN or may be using other parameters. Do anyone know how to calculate effective SSN. i.e ...
130 views

### How to calculate geocentric conjunction time and moon altitude at a given time

Umm al-Qura calendar of Saudi Arabia determine the new moon if these criteria meet at 29th day: The geocentric conjunction occurs before sunset. The moon sets after the sun. I've got the formula ...
870 views

### Why doesn't the sun pull the moon away from earth?

If the suns gravitational pull is strong enough to hold much larger masses in place (all the planets) and at much greater distances (all planets further away from the sun then earth) why does it not ...
56 views

### Are there naturally radiation shielded areas on Mars? (shadowed by terrain formations)

Mars' thin atmosphere and lack of magnetosphere exposes its surface to lots of Solar UV radiation and cosmic radiation. But Mars also has some dramatic altitude gradients in for example Valles ...
133 views

### Why was this asteroid (4864 Nimoy) chosen to be named after Leonard Nimoy?

The asteroid 4864 Nimoy was recently named after Leonard Nimoy. It was discovered on September 2, 1988 so it went nearly 27 years without a name. Why was this asteroid chosen to be named after him? ...
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### Will Hubble's law always be accurate?

We have Hubble's law: v=Hd where H is the Hubble parameter, which is decreasing in value, but it will be constant in the distant future. So, assumming the Standard Model of Cosmology holds true, ...
81 views

### Is there a mechanism that makes small moons more rounded than comets?

67P/Churyumov–Gerasimenko has a highly irregular dumbbell shape. But the sample of comet shapes observed is very small, so I wonder if irregular shape is the norm for comets and for small moons. Many ...
80 views

### How did WASP-18b exoplanet form?

I am new to this community and not quite sure if this is an appropriate question to be asked here. Anyways its just my curiosity. As far as I could know about WASP-18b is that, it orbits very close to ...
206 views

### radial velocity fitting of a binary

I have two series of velocities (HJD, $v_{1}$ and $v_{2}$ ), how to fit in detail? There is any formula on the web? $sine$ curve is easy, but I need to consider an eccentric orbit. Suppose we can ...
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### Halpha velocity fields of spirals falling into a cluster

What kind of impact would you expect ram pressure stripping / tidal interactions / harassment / interactions with the cluster potential (etc!) to have on the h-alpha velocity fields of infalling ...
135 views

### Day Length on Double Planets

Assume two similarly sized bodies tide-locked to one another orbiting a barycenter between the two. That barycenter orbits a star. Since the two are tide-locked, their sidereal rotational period and ...
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### How can we tell how many exoplanets a star has?

Part of this answer (discussing the moving center of mass of our solar system) explains that this movement is one way we know a star has planets: Bonus: We use this phenomenon to find planets ...
262 views

### Is our universe included inside a black hole?

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 ...