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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1answer
195 views

What do you call the period after sunrise when the sky is bright?

At sunrise, the sky isn't actually up in the sky yet. Twilight occurs before sunrise, then at sunrise the leading part of the sun crosses the horizon. But, the sky isn't bright yet. It takes some time ...
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0answers
50 views

Why stars twinkle but planets don't? [duplicate]

I am not from a physics background. I came to know this while studying probability? Is this because the planets are nearer than the stars so we get average behaviour rather than random. Is law of ...
5
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2answers
176 views

Celestial Time-Keeping and Navigation

Say, for sake of argument, someone was randomly transported in time and space. Would it be possible for them to determine their location on Earth and the current time using just observations of the ...
3
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1answer
440 views

Ephemeris calculations: Light time correction of the moon

I am currently trying to calculate apparent positions from raw JPL data. I've got it pretty much figured out, but there is one thing that's bugging me: Has the light time correction of the moon to be ...
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2answers
106 views

Is there a star catalog for download?

Is there a downloadable star catalog which not only includes positions, but also spectral class, size, etc.? A CSV file would be great for the sake of easiness.
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0answers
76 views

Why is infrared imagery of Mars' surface sharper / richer in contrast than that from the visible spectrum?

Looking at the terrain of Mars through Google Mars, it seems to me that the infrared imagery is much crisper, the images from the visible spectrum seem to be somewhat hazy. I'm wondering if that is ...
10
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2answers
336 views

Does the Milky Way have dark matter satellite galaxies?

This recent paper by Weinberg et al. discusses that one potential problem with our current model of Cold Dark Matter (CDM) is that is predicts a greater number of satellite galaxies for the Milky Way ...
17
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1answer
597 views

How fast is the Earth-Sun distance changing

This is inspired by Evidence that the Solar System is expanding like the Universe?, which referenced an article by G. A. Krasinsky and V. A. Brumberg, "Secular Increase of Astronomical Unit from ...
6
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1answer
94 views

How far can one look into space while relying on light in the visual spectrum?

Put the other way around. From how far does visible light reach the Earth to be observable by a telescope that operates in this spectrum? Gas clouds for instance absorb light. A star behind such a ...
8
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1answer
392 views

Why are telescopes on top of Mauna Kea instead of Mauna Loa?

Many large and important telescopes are located on top of Mauna Kea on Hawaii. This is a great location for many reasons: it's tall enough to be above the weather, an inversion layer at night keeps ...
2
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3answers
214 views

How early might a moon-sized asteroid be detected?

If an enormous asteroid, approximately the size of our moon (~2000-mile diameter), was passing close to Earth, how early might we detect something that large? Or alternatively, how close could ...
4
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2answers
332 views

How many stars did people think there were in the 11th century (or thereabouts)?

I hope this isn't too off-topic. Someone showed me a reference to a French, 11th century biblical commentator who implied that there were over 600,000 stars. This got me thinking, how many stars did ...
3
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1answer
77 views

Primary direction in planet-centered equatorial reference frame

I am given the classical orbital elements of the orbit of a spacecraft around a planet which is not the Earth, say Venus. I assume those are referred to a reference frame whose fundamental plane is ...
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486 views

Map of the gravitational strength of the solar system

I am looking for a map or plot of the gravitational strength in the solar system. In an ideal world there should be something like google earth to move around in the solar system, zoom in and out and ...
8
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2answers
265 views

Why is the summer, in the temperate latitudes, in average, hotter that the spring?

It is common knowledge that the transition from the Spring to the Summer season occurs in the Summer Solstice when the "Sun reaches its highest excursion relative to the celestial equator on the ...
1
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1answer
66 views

Astronomical measurements and data

For the sub-nuclear physics there is a database of the Particle Data Group, I was wondering if there was a similar on-line collection for astrophysics, such as energy absorption and emission spectra ...
6
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3answers
203 views

Can gamma rays be used to investigate heavenly bodies?

This is a very layman level question. I watch a lot of documentaries, that's my only qualification. I have seen in documentaries that gamma rays have an extraordinary penetrating power. So if we could ...
5
votes
1answer
146 views

Why is there a line in the middle of the Planck full sky map?

Why there is a straight line (or perhaps a flat surface) in the middle of the Planck full sky map? and zoom (it makes it seem that the big bang was a collision between two unknown surfaces)
8
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2answers
389 views

How does dark matter halo outside a galaxy help to explain galaxy rotation curve?

How does a dark matter halo outside a galaxy help to explain a galaxy rotation curve? Suppose for simplicity we use a model of a star rotating about a more massive star in a fixed circular orbit. For ...
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1answer
285 views

How does color of galaxies explain their distance?

Why do distant galaxies have different colors than closer ones?
6
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1answer
344 views

How big of a telescope to view Gliese 581g in great detail?

I've always been interested in mega sized telescopes and how big they would have to be to see exoplanets in great detail. So, Gliese 581g is 22 light years away. Could we build a telescope in space ...
3
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2answers
167 views

Can the axis of rotation of a celestial body point in any arbitrary direction?

I am developing a small computer program that involves moderately simple simulation of elliptical Kepler orbits for fictional, generated star systems. I'm doing this without much prior knowledge of ...
3
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0answers
63 views

How to predict Iridium Flare?

I want to find out how to predict Iridium flares, but I don't know where to start. If I know Solar position, Iridium satelites' TLE and it's shape, I need a magnitude(time) function for some place on ...
2
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2answers
228 views

How is the sun's equatorial circumference measured?

How is the sun's equatorial circumference measured by scientists?
6
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2answers
228 views

How to cut a stone on on a White Dwarf

I've heard that white dwarfs are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that?
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0answers
156 views

How do I obtain the Point Spread Function (PSF) of a ground telescope?

I have some galaxy kinematic maps (velocity maps) extracted from Integral Field Spectroscopy (IFS) datacubes. Like any observation data coming from a ground telescope, these velocity maps include (ie: ...
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1answer
48 views

Dimensions of a variable celestial body?

I read (extern link to a filehoster, page 163 section 4.8) that a variable celestial object like a pulsar or quasar must be smaller than the distance the light travels in its variation period. Can ...
3
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1answer
206 views

Calculating the length of day at any time of the year? [duplicate]

Is it possible to calculate the length of the day at various location (distances) from the sun? I hear agricultural scientists are able to do that. To make calculations easier assume there is no axis ...
3
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1answer
102 views

Galaxy Kinematic Fitting: How to deal with Point Spread Function (PSF)

The past few months I have been studying astronomy and Integral Field Spectroscopy (IFS). What I want to do is to fit a galaxy kinematic model to data (ie: estimate the model parameters that give the ...
8
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1answer
264 views

How can one get the eccentricity of the orbit of the Sun around center of the Milky Way?

How can one get the eccentricity of the orbit of the Sun around center of the Milky Way? Can it be measured?
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2answers
142 views

starlight flux on earth

I want to calculate if it is possible to photograph a subject lit only by starlight. I found one website claiming that a starlit scene is lv = -15 (daylight is lv 15, or 2^31 times brighter), but he ...
6
votes
1answer
103 views

Astronomical-wavelength radio (AWR) transmissions between cosmic plasmas?

My son asked me if electromagnetic waves longer than radio exist. I told him that even though physics permits such waves, there are no antennas long enough to radiate or detect them. However, on ...
7
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1answer
574 views

Distribution of star colours in a galaxy

I'm trying to randomly generate a representation of a galaxy. I have some Idea on the spatial distribution of stars within a galaxy, and I can find plenty of material on the colour of stars, but ...
4
votes
2answers
532 views

Recent Planck probe results: how unexpected?

The data from the Planck probe's observations are in, and according to the European Space Agency they show a "hemispheric asymmetry in the cosmic microwave background (CMB)". Quote: an asymmetry ...
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45 views

Estimating the present state of stars [duplicate]

Many time while reading through astronomy articles on the stars most of then thousand of light years away from earth. I have wondered how do astronomer know about the present state of star if we are ...
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1answer
100 views

What would happen if the moon was in perpetual opposition of the sun [closed]

What would happen if an artificial force made the moon to stay at a perpetual opposition from the sun? Assume that the artificial force necessary is possible, and capable of making the moon stay at ...
-1
votes
1answer
381 views

How do you calculate the Milky Way’s galactic year? [closed]

The Solar system moves at a speed of 220 km / s around the galaxy. It’s about 27,000 light years from the Galactic Centre. How long does it take for the solar system to orbit around the Milky Way? ...
1
vote
1answer
141 views

How far to the 'edge' of the galaxy?

Wikipedia lists the average thickness of the milky-way to be about 1,000 LY - but where (roughly) within that is the sun currently? In asking this, I'm fully aware that there's no well-defined edge - ...
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2answers
306 views

Planet in which satellite(moon) and star(sun) appear together once a year

With a hypothetical system, where the moon would be always on the opposite side of the planet than the sun, in a way that the moon would only be visible at night on the planet. I don't know if this ...
9
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1answer
2k views

Do all known planets and moons have magnetic field?

In this Wikipedia article it is stated, that magnetic field of Earth is caused by currents in her core. The same origin is for Jupiter magnetic field. For Moon (article) there is a magnetic field, ...
8
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3answers
299 views

Parallax, obliquity, precession, and Orion?

Today, the obliquity of the earth is about 23.4°. 6500 years ago, it was about 24.1° Imagine the blue square is the constellation of Orion, and the yellow star is the sun. Viewpoint B is you, on ...
2
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3answers
842 views

Distance away from earth to see it as a full disk [duplicate]

This question is more space-related than physics-related, but here goes... How far away the earth would I have to be in order to see the earth as a full disk? What I'm looking for is a distance in ...
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0answers
26 views

What's an equation for two astronomical entities both of 4000 tonnes in weight, colliding? [duplicate]

I have next to no knowledge of any physics, but would be happy if you could answer my question... I want to know an equation for two astronomical entities such as the star Sirius (2.02 solar mass) ...
1
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2answers
551 views

Aligning images of starfields

I have two images taken within 30 minutes of each other in the same part of the sky. They are very similar but are slightly offset due to the Earth's rotation and other factors. I know: the X, Y ...
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2answers
140 views

Is it possible that universe might not be speeding up expansion?

I'm not sure but I was thinking of galaxies shrinking with time while still moving apart from each other at almost a constant speed or less (i.e: uniform/slightly decelerating expansion). This may ...
5
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1answer
409 views

What planets are visible to the naked eye from Mars?

Here on Earth we are blessed with being able to see some other planets, Mars & Venus etc, with the naked eye on a fairly regular basis thanks to the distance between the planets. What about from ...
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2answers
398 views

Curiosity Rover (MSL): current coordinates

I'm looking for information on the current coordinates of Mars Science Laboratory's Curiosity Rover. I've only found the landing site coordinates 4.5895°S ...
18
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3answers
199 views

What happens to the electron companions of cosmic ray protons?

If primary cosmic rays are made mostly of protons, where are the electrons lost, and does this mean that the Earth is positively charged? Does the sun eject protons and electrons in equal number?
8
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3answers
156 views

How do we measure the range of distant objects despite relativistic effects?

When we observe astronomical objects like distant galaxies there are several complicating factors for estimating the distance: Relativistic speed result in length contraction Relativistic speed ...
19
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2answers
649 views

Optimal telescope size?

Consider a diffraction-limited telescope with unobstructed aperture $D$. Such a scope is capable of yielding an angular resolution $\alpha$ that scales as $\lambda/D$, with $\lambda$ denoting the ...