# Tagged Questions

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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### What is the meaning of a negative Galactic longitude?

What is the meaning of negative longitude in Galactic coordinate system? Does the longitude $-65^\circ$ equal $295^\circ$?
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### Can astronomers observe neutron stars optically?

Are there any neutron stars near enough for astronomers to observe them optically? If not, then how close are we to having the technology to do so?
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### How are coherent astronomical objects imaged?

I am studying astronomical imaging, and am curious about how to image astronomical objects which are coherent. Stellar interferometry measures the mutual coherence function of a star, and then uses ...
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### Relationship between Mars and Earth rotation

Is it by pure random chance that Mars and the Earth have nearly the same day duration (Mars day is barely 40 minutes longer, which is just 3% difference), or there is some causal relationship between ...
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### Books for someone interested in physics/space [duplicate]

As an avid reader of more realistic SF and someone who has always been interested in physics and astrophysics, I was wondering if someone could suggest both some introductory books on the subject, and ...
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### Determining Mass of Spectroscopic Binaries

I know that the mass of a binary star system is given by Kepler's Law: $$\mathrm{m_1 + m_2 = \frac{4 \pi^2 r^3}{GT^2}}$$ Further we know that: $$\frac{r_2}{r_1} = \frac{v_2}{v_1} = \frac{m_1}{m_2}$$ ...
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### Any good statistics books under the context of astronomy? [on hold]

I just started a position as a research aide with the cosmology group at Argonne National Lab, and am working on creating and finding correlations within velocity dispersions of galaxy clusters. After ...
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### Negative Parallax

I am constructing a Hertzsprung-Russel diagram for stars within a radius around Pleiades and have repeatedly come across stars that have negative parallaxes. For example, http://vizier.u-strasbg.fr/...
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### How does Torque from tidal forces scale with distance

I read in a paper a while back that the torque on a body caused by differential rotation and tidal forces scaled with distance to the power of 6. That struck me as odd since the tidal force scales ...
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### What do the colors in false color images represent?

Every kid who first looks into a telescope is shocked to see that everything's black and white. The pretty colors, like those in this picture of the Sleeping Beauty Galaxy (M64), are missing: The ...
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### Why don't solstices coincide with temperature extremes? [duplicate]

In northern hemisphere, the highest temperatures are usually in July — in the middle of calendar summer. See e.g. the climate chart on this wikipedia page. But the solstices are on 20-21 of June, ...
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### Short gamma ray burst redshift

I would like to know what kind of methods are being used to infer the redshift distance of GRBs. Some background: I recently went on two sites; grbweb by IceCube and Fermi GRB database. On grbweb ...
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### What is exactly the “progenitor bias”?

I am taking a course in astrophysics and my teacher mentioned different biases that are present when taking a sample of galaxies: the progenitor bias and the Malmquist bias. I understand very well the ...
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### Why does the light side of the moon appear not to line up correctly with the evening sun?

I live at roughly $(52.4^\circ,-2.1^\circ)$. On sunny evenings I've often looked at the Moon and the Sun and noticed that the light part of the Moon does not appear to line up with the Sun. For ...
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### How to read numbers reported in this LIGO paper?

I am not sure how to read the numbers in this excerpt from the abstract of GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence: Are the +/- small ...
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### 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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### “Reverse engineering” of a horoscope?

I'll start with a disclaimer -- this is not a question about astrology itself, I'm neither trying to refute nor to defend astrology. I'm interested in purely technical things, which are mostly ...
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### How do we decode the image formed by a gravitational lens?

Using our own sun as a gravitational lens, we can scrutinize planetary surfaces in distant solar systems with a good deal of accuracy. How do we translate this smeared out and curved image into a ...
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### What time scale is used by the JPL HORIZONS system?

I'm confused by the ust of the term "UT" in the description of time scales used by the JPL HORIZONS system. Their manual states that UT is Universal Time This can mean one of two non-uniform ...
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### Uncertainty in the distance between Sun and other planets

I have read about the orbit distances between Sun and the planets and have come to know for example: Earth is around 150 million km away from the Sun. However I have seen that tht value is only an ...
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### Can the “Milky Way” galaxy be seen by the naked eye in a clear sky?

Is this photo "real"? Are the stars not super-imposed in the image?
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### What is the farthest planetary body or star system object we have observed using visual light?

What is the farthest object which we can get a direct Detailed visual image of using visible light which appears more than just a dot and falls into one of the following categories: Planet Satellite ...
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### GR Verification for a Charged Black Hole

For a charged ($Q$) rotating ($L$) mass ($M$), the Kerr-Newman equations give the angular deflection of light. Has there been observational verification (I would prefer to use only the angular ...
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### About the hump on galaxy rotation curves

The past days I have been studying the rotation curves of disk galaxies and I am currently trying to understand how we can extract information about the dark matter of a galaxy by looking its rotation ...
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### How can i estimate the apparent size of an object?

I would like to be able to estimate, the apparent size of some object. The motivation behind this, is to use the correct numbers, in a sci-fy novel i am writing. Só, i want to be able to calculate, ...
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### What is the farthest-away star visible to the naked eye?

My girlfriend and I were watching Cosmos, and something Carl Sagan said got us wondering what the farthest-away visible star is. Obviously "visible to the naked eye" is a fuzzy concept that might have ...
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### How do we filter out radiation from galaxies from the cosmic background radiation?

When a whole sky view is done to get a picture of the cosmic background radiation the radiation from our Galaxy is filtered out, and we are left with a picture which show radiation coming, more or ...
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### How to determine day/night based on latitude, longitude and a date/time?

Is there a simple method of determining, given a UTC date/time, whether it is day or night at a given lat/long coordinate? I am currently using a formula based on a Sunrise/Sunset Algorithm from the ...
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### How to interpret these gravitational lensing data?

The data I am trying to understand this gravitational lensing data in the link above. However, unfortunately I don't have an extensive knowledge in physics. Could someone please tell me what each of ...
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### Do satellite galaxies have the same proportion of dark matter as “ordinary” galaxies

My question is relatively straightforward: Do we know if satellite/ dwarf galaxies contain the same proportion of dark matter to ordinary matter as "regular" sized galaxies? The Milky Way, for ...
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### Determine date of birth from “astrological” signs?

Suppose someone tells me what constellation the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn were in when they were born, and the information is astronomically accurate (ie, not astrological ...
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### World's Largest Radio Telesope : How accurately does it need to be figured?

In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ...
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### Very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth

I need a very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth. Currently, thanks to the algorithm which generates the position ...
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### Error measurement barycenter of the Solar System - NASA data

What are the possible measurement error barycenter of the Solar System in NASA data? In the data JPL's HORIZONS system for NASA (http://ssd.jpl.nasa.gov/?horizons): Target Body: Solar System ...
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### Translational Velocity

Is the translation velocity equivalent to its real velocity or radial velocity? Online sites and textbook are saying different things, So Im not too sure what is going on
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### Why don't reflector telescopes place their reflectors at an angle?

To avoid placing a secondary mirror in front of the objective mirror, why not tilt the objective and design the eyepiece in such a way that comatic aberration is minimized?
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### Why is a new moon not the same as a solar eclipse?

Forgive the elementary nature of this question: Because a new moon occurs when the moon is positioned between the earth and sun, doesn't this also mean that somewhere on the Earth, a solar eclipse (...
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### What is the estimator that used to de-rotation of CMB polarization? [duplicate]

For de-rotation of CMB polarization we need to use of estimator for rotation angle. and used many estimator for this process.
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### Hubble time and age of the universe

I'm having trouble with the following derivation of the 'age of the universe': http://imgur.com/gRvLWX8 The parts I'm struggling to conceptualize is what a 'universe expanding' means, and also why ...
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### The impact of the Oort cloud to change the barycenter of the solar system

Is the Oort cloud changing the position of the barycenter of the solar system? Does it affect in a significant way? How significant?
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### Solar time correction due to longitudinal difference

I've been always calculating the correction in solar time due to difference between observer's meridian and the meridian on which the local standard time is based using the following formula "Design ...
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### Different width of spectral lines for different groups of stars

As seen in an HR-diagram, a certain stellar classification can correspond to more than one group/sequence of stars (G5 could for instance be either a giant, main sequence star or a white dwarf and so ...
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### Names, maps for Milky Way dust clouds? (Dark Cloud Constellations)

There is a nice image of the Milky Way, labeled with constellations, at 360°x45° panorama with constellations: It leads me to wonder how much we know about the Great Rift, Coalsack and other ...
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### Calculating the Diameter of Jupiter through Image [closed]

I was trying to calculate the diameter of Jupiter from a picture I took of it. Here's the information I was able to get that I needed to calculate the diameter: Focal Length of Telescope: 1.2 m ...
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### Can you see yourself in space? [closed]

Can one see them self in space if no near by star was in view? Is there enough star light to read once your eyes adjust?
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### Gamma Ray Burst data

I wanted to know if there was some database for gamma ray burst (GRB) data. I would like to get the luminosity and duration of recorded GRBs. So far, I have come across this website, but since I do ...