All Questions

131 views

How many actual stars are Polaris?

I am getting conflicting accounts everywhere. I heard astronomers saying Polaris is a 3-star system. Some say they are binary but are optical-doubled with a 3rd. ...
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Are a white hole's forces completely opposite of a black hole? [duplicate]

Would not all the forces of a black hole be opposite if the light is escaping from it? For example, rather than it attracting everything to it, would it repel everything?
69 views

How was Earth's “quasi-satellite” 2016 HO3 “first spotted” and it's orbit determined?

Under a question I asked a few days ago Have there been any documented mini-moons since 2006 RH120? @Hobbes mentioned the recent news about 2016 HO3 - a near-Earth asteroid that stays near Earth ...
38 views

How can I convolve a template spectrum with a photometric filter response spectrum?

Suppose I have a template stellar population spectrum (say, from Bruzual & Charlot 2003) which runs from like 1000 Angstroms to 160,000 Angstroms and which has x-axis wavelength units of Angstroms ...
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I am a beginner Does planets exhibit retrograde motion (eg Mercury and Venus) only because of earth rotation? Or is there any other reason? Please clarify
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What starting circumstances have to be for “grand tack” hypothesis to work, and why they are lacking in other planet systems(as far as we know)?

I recently read a bit about "grand tack" hypothesis. It was extremely interesting and it seems to reasonably well explain many features of our solar system. At the same time it supposedly is ...
81 views

How to find which part of the sky a photo contains?

I was taking some photo stacks yesterday, and I also took a plenty of random ones (pointed not at a specific object) too at 200mm. However, I've ended with a shot but I have no idea where I pointed ...
119 views

Could the word “multiple stars” include binary stars?

We are translating some illustrated book for kids about astronomy, and then have a question as in the title. Referring to Wikipedia etc., It appears that "binary stars" represents the star systems of ...
46 views

Survival on a rogue planet [closed]

Are there any planets not orbiting a celestial body which can support life despite the temperature? Also what is the absolute minimum temperature that life can survive in?
24 views

Negative Spectral Flux Density

I am working on a project and using some satellite images. In some of the images the Spectral Flux Density is negative. What does it indicate?
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Can a rogue planet neither orbit around a star nor a galaxy?

As we know, rogue planets don't orbit around a star, how about galaxy? Can a rouge planet not orbit around a galaxy?
27 views

How do I apply a velocity shift to a wavelength array with uniform logarithmic spacing?

Suppose I have a wavelength array for a spectrum in units of Angstroms. Suppose further that the wavelength has "uniform logarithmic spacing" such that if I just take the difference in Angstroms ...
5 views

How do I reduce planetary photometry to standard viewing geometry using phase angle?

I'm trying to make light curves for Pluto using old data. Most papers give magnitudes "reduced to standard viewing geometry" of r = 39.5 AU, Δ = 38.5 AU, and α = 1 degree, where r is ...
34 views

“Extinct Species” of meteorite - how quantitative is the statistical analysis?

This recent paper in Nature A new type of solar-system material recovered from Ordovician marine limestone is available to read on line, and Figure 3 is already widely publicized. Comparison of ...
135 views

why was the probability of one in 10 billion per planet considered highly pessimistic by a recent study on aliens? [closed]

A recent article about the existence of extraterrestrial life claimed that "unless the probability for evolving a civilization on a habitable-zone planet is less than one in 10 billion trillion, then ...
120 views

Techniques for locating origin of gravitational waves

The gravity wave detections (GW150914 and GW151226) have both been ambiguous in their exact position, the LIGO papers (GW150914 and GW151226) give no precise information about the location of the ...
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Which astronomical objects do we have images of, taken at ground level? [closed]

I am looking for images of astronomical objects taken at the ground level of the actual object, by something on the actual object, i.e. the Mars Rover. Is this the complete list and accurate?. ...
163 views

Is it possible for a moon to continuously have a side facing its star whilst orbiting a planet?

For example; is there any possibility for the moon to always have a side facing the Sun whilst orbiting Earth? And if so then what would the day cycle be like?
109 views

If the planets only attract, then how can they stay in their orbit?

Gravity is related to mass, and gravity is an attracting force on every body. Then what happens when bodies only attract each other..without repulsion they may strike the sun. I think there must be a ...
141 views

Is Earth slowing down in order to stay on its orbital track?

The Sun is losing some of its mass during explosions. The Gravitational force between Sun and Earth will change (probably decrease). If Earth maintains its speed, it will change its orbit. Hence, ...
41 views

Data Analysis: Image Sharpening through Posterisation

I had this image, a picture of Jupiter: I wanted to measure the pixel diameter of Jupiter. As evident, the image is quite blurry, and thus, many value of equally justified pixel diameters can be ...
30 views

What (actually) is a radio “homology telescope” and will the 500m dish in China be one?

This question is about design aspects of large radio telescope dishes which allow them to flex under the influence of gravity as they change elevation angle, and still maintain good optical ...
52 views

Have any co-orbital exoplanet pairs been discovered (and not subsequently retracted)?

For this question, I think a good working definition of co-orbital configuration would be two bodies orbiting around a third much larger body in a 1:1 resonance and where neither mass is negligible. ...
30 views

How did single dish (or single receiver) radio telescopes originally generate images?

That actually sums up my question nicely: How did single dish (or single receiver) radio telescopes originally generate images? - or at least 2D intensity maps or contour plots. Early radio ...
22 views

What is the highest granularity focal-plane array on a dish radio telescope?

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 ...
67 views

A quick (elementary) check on arsecond conversion to sky distance in parsecs

I just wanted to double check I had something correct. If an object, say a nebula, is measured to roughly have a diameter or extent of, say, 250 arcseconds, would its diameter in parsec simply ...
89 views

Is time taken into account by astronomers when creating and using maps of the universe?

There's really two questions I'm asking. Firstly, when maps are produced of stars and galaxies, are they just produced as we see them now from our viewpoint? Or are they based on the motion of those ...
44 views

What is the cut-off point of $\frac{dF}{dr}$ beyond which no tidal locking will occur?

I am a beginner, please pardon my non-use of proper astronomical terms. I would appreciate proper edits to my questions. I have learned that when the $\frac{dF}{dr}$ is a very big negative number, ...
12 views

how the diameter of a galaxy is measured [duplicate]

we are simply measuring the wavelength.How the diameter of a galaxy is measured using this?Does some other methods are there to measure this diameter?
79 views

Can a gas giant be hollow?

Let's think of Saturn, because of its density. Can there be a place near the center of the planet where the gravity upwards is more than towards the center, and with an atmosphere that is more ...
107 views

What is the speed of time?

From the theory of relativity, if any object is moving with the speed of light or more than the speed of light, then the time stops or seemed to be stopped for that object. That means, that the speed ...
177 views

What is the Age Difference Between Earth & Jupiter?

What is the age difference between Jupiter & Earth. Which planet was formed first, or were they formed at the same time.
33 views

Does Triton trigger the active atmosphere of Neptune?

As we know the atmosphere of Neptune looks more active than Uranus', is this due to the tidal forces caused by the retrograde orbit of Triton around the planet?
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How to show that the Jeans Criterion for Mass, Radius and Density are equivalent?

The gravitational collapse of a gas cloud can be described by the Jeans Criterion for mass, radius and density of the gas cloud, which is (c stands for cloud): M_J = (\frac{5kT}{G \mu m_H})^{3/2} (...
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Luminosity L(t) for a homologously contracting star

I'm dealing with a homologously contracting star with Mass M, Radius R and a gravitational binding energy of $E = -a GM^2 / R$ (a is a constant). I was looking for a way to find an expression ...
24 views

Deep space craft antenna aiming [migrated]

In order to aim antenna at Earth, how do unmanned space crafts find it own orientation (xyz position in space, what direction is it flying and which direction the antenna is pointing)? Are they are ...
205 views

Is there a limit to how hot an object an get?

Temperature is a measure of the average kinetic energy of particles in a given place (correct me if I am wrong) so there must be a definite limit to heating like there is an absolute zero to cooling. ...
43 views

Is our universe expanding? [duplicate]

Is our universe is expanding or contracting. And if it is doing so then what is the basic principle behind it. Is it related to the net energy of the universe or something else.
132 views

Is our central black hole actually at the CG of the galaxy?

It seems fairly certain there is a large black hole, about 25,000 ly from Earth roughly in the center of our galaxy, in the direction of the Sag. A radio source. • In fact, is it thought to be ...
151 views

Conventional matter to dark matter ratio, outside of galaxies (Bounty!)

I'm pleased to offer a bounty to attract more attention to the fantastic Astronomy site. Consider say this outstanding diagram from another question, To begin with galaxies have a typical ...
73 views

Oscillation in tilt of the solar system

I know that the solar system is tilted 62.6° to the plane of the galaxy. I'm curious whether this angle changes over time, and what are the extents and time frame of any such oscillations if they ...
84 views

Higgs Bosons in the centre of Black holes or extremely large stars [closed]

With the discovery of the Higgs Boson as the mass carrier, what is the possibility at the centre of a black hole being so dense and gravity so infinite that the structure of a proton or neutron are ...
33 views

Are there currently observed systems of close (narrow) binary brown dwarfs?

All over the Universe, there are (gravitationally bound) binary star systems. Considering the huge number of brown dwarfs, are there currently known double systems of gravitationally bound binary ...
235 views

Milky Way mass fraction breakdown review

I'd like to know a breakdown of the mass of the Milky Way, by the major categories. So, something like ...
525 views

Definition of stellar core?

This is a basic question, but I may as well ask it. I had always thought that the core of a main-sequence star is defined as the part hot enough for nuclear fusion. Some dictionaries seem to agree ...
45 views

What kinds of stars would it be possible to observe in M31 with a small amateur telescope?

I was wondering what kinds of stars would be visible in M31 and other nearby galaxies using a moderate (~8") telescope and a CCD camera. This would be a limiting magnitude of around 17. I have heard ...
21 views

What is the magnitude of variation of Earth's orbital inclination?

Please excuse if this has been asked and I just didn't find it. I have found several references that indicate that the inclination of Earth's orbit varies over a period of ~70,000 years, but I can't ...
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Would the (orbitting) speed of the earth change if suddenly the sun disappear and the earth is thrown into space?

Usually an orbit is considered as an acceleration. So fe the earth has a speed of about 100.000km/h around the sun. Now I think there is some relativity involved, so from which point of view shall we ...