0
votes
0answers
30 views

Does any satellite communicate only through laser? [migrated]

I have read (here) + heared (on astronomy podcast) that radio waves decay or are undistinguishable the more distance they travel. Do any of man made satellites communicate with Earth solely by ...
1
vote
1answer
43 views

What is “emission measure”?

Many papers mention emission measure, and some of them give the expression of EM, BUT there is no clear definition of EM. My question is what EM is on earth? Its unit is supposed to be cm-3. How to ...
7
votes
1answer
110 views

Why don't storms on gas giants move to the poles, like hurricanes on Earth do?

On Earth, hurricanes usually move from the equator to the poles. But if you look at a picture of Jupiter, you'd see that the Great Red Spot isn't anywhere near the poles. So the question is: why don't ...
4
votes
1answer
63 views

At what size to objects burn up in the atmosphere when falling from orbit?

As the title suggests, I am wondering the maximum size an object can be so that it will completely burn up when entering and falling through earths atmosphere. I'm focusing on man made objects, not ...
5
votes
1answer
40 views

What are the prerequisites for a meteorite to reach the ground?

I'm sure it's a function of atmospheric entry angle, meteorite mass (and possibly composition/density), and its velocity, but what function is it? Above all, how does it depend on velocity? Will the ...
1
vote
1answer
42 views

What effect does a natural satellite have on a planet's rotation and revolution?

how is the rotation and revolution of a planet that does not have a natural satellite different from a planet that has say 1 natural satellite (ex. earth and moon system).
7
votes
4answers
191 views

Why does it make sense to say the universe has no centre?

If we suppose we and everything in the universe is perfectly flat. That is, we have width and depth, but no height. And we are situated on the surface of a balloon blowing up with air and expanding ...
-6
votes
0answers
85 views

How old was “student-Earth” when life first formed? [closed]

this section is meant to explore the relative timings of various important events in Earth's history by re-imagining Earth as a 20-year student. You will need to scale geologic time from the age of ...
-2
votes
0answers
28 views
3
votes
1answer
34 views

Where's the Prime Meridian of celestial coordinates

...or what's the 'direction of vernal equinox'? For both Ecliptic and Equatorial coordinate system, the Wikipedia article gives "Primary direction (0° longitude)" - "Vernal Equinox", linking to ...
1
vote
1answer
51 views

Why do PMS stars on the Hayashi track remain at a constant temperature while they contract?

Why do pre-main-sequence stars on the Hayashi track remain at a constant temperature while they contract? I've read the Wikipedia article, so no need to repeat the derivation. What I took away from ...
4
votes
2answers
49 views

Which planets have abundant amounts of photoluminiscent matter?

Which planets have abundant amounts of photoluminiscent matter? Photoluminiscent or chemoluminiscent whatever the glow-in-the-dark stuff it may be. Planets or bodies which have good enough the ...
3
votes
1answer
130 views

How to calculate the heliocentric velocity of an object?

My task is to calculate the heliocentric velocity of an object to correct for wavelength in a spectrum. I have the RA, Dec and observation date, and I know that the NED velocity correction ...
29
votes
5answers
5k views

Why hasn't the “9th Planet” been detected already?

In the comments to this question, there was considerable doubt placed as to the subject of if the so called "9th planet" really exists. That wasn't really the intent of the previous question, so I ask ...
5
votes
1answer
91 views

How can you determine the initial volume of a planet's atmosphere?

Since the surface pressure of a planet is determined by the mass of the column of gasses above it one would surmise that to determine the pressure you must know the volume and mass of the atmosphere. ...
1
vote
2answers
33 views

Terminology: Is there a name for the points on the surfaces of tidally locked parent/satellite bodies that always face each other?

This is purely a question about terminology, one that has eluded my googling efforts. When a satellite and its parent body are tidally locked to each other, there is (in an ideal case) a single ...
1
vote
2answers
24 views

Are there any bright non-stellar objects which make up asterisms?

Hopefully the title is very self-explanatory. I was wondering if there were any non-stellar objects, such as bright galaxies, which when looking with the naked eye were mistaken for stars in the time ...
4
votes
3answers
160 views

What types of signals is SETI (and other such efforts) looking for?

This seemed to be the closest group for this question. Every few months there are a few articles asking "Are we alone in the universe" which focus on the Fermi Paradox, the Drake Equation, and end by ...
2
votes
1answer
61 views

Name for 1-e and 1+e terms?

In several equations of orbital elements (such as the determination of true anomaly from mean anomaly), the terms 1-e and 1+e appear. These are the ratios of the orbital periapsis and apoapsis to the ...
3
votes
1answer
72 views

Would I actually be able to see Ceres without shining a really bright torch onto it?

NASA's put out a semi-CGI video of a Ceres flyby using material from the Dawn mission. Now I realise that visibility is relative, even on Earth: I can walk into my basement and not be able to see ...
1
vote
2answers
40 views

Is Higgs Boson mass equal to the missing mass of dark matter?

Sorry if this is a very lay question. I am just an armchair physicist. The Higgs Boson was just recently discovered, and it has a mass which is considerably larger than a proton. If this Higgs Boson ...
7
votes
1answer
113 views

Why does the planet Saturn have numerous (62) moons compared to the rest of the planets in the Solar System?

Saturn is a gas giant like Jupiter. It has everything from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with ...
3
votes
1answer
51 views

Is it possible to get the distance to a star in the IPHAS DR2 catalog?

I'm looking at the IPHAS DR2 catalog. It has the Right Ascension and Declination but I'm not seeing any distance information (lightyears or parsecs). I'm wondering, given the columns in the dataset, ...
3
votes
1answer
192 views

What uncertainty does an error bar signify in astronomy?

When an astronomer talks about her/his topic and shows an X/Y-plot with error bars. What should one assume that those error bars represent? 1 standard deviation? Or 2? Or some specific significance ...
3
votes
1answer
48 views

Stability of orbital resonance

Recently I've become more interested in the topic of the stability of planetary systems. I have been reading about it and it seems that orbital resonances play an important role in the stability of ...
1
vote
1answer
367 views

What would happen if a wormhole gets swallowed by a black hole?

Assume wormholes exist. One hole allows matter to pop out of another hole somewhere else in the universe. If one end of the wormhole is swallowed by a black hole, then no information can get from ...
2
votes
0answers
54 views

Would the existence of Planet Nine rule out the possibility of a sixth giant planet?

I'm aware that there have been attempts to simulate the evolution of the Solar System with six giant planets1, as opposed to the traditional four or five. The recent proposed Planet Nine would ...
4
votes
3answers
266 views

Could the KIC 8462852 (Alien megastructure star) be explained by orbiting gas clouds?

I was wondering about the light dimming of the 'alien megastructure' star. From what I understand, for it to be a planetary body, it would have to be some 20 times the size of Jupiter. Is it possible ...
8
votes
1answer
405 views

Why does the moon sometimes appear giant and a orange red color near the horizon?

I've read various ideas about why the moon looks larger on the horizon. The most reasonable one in my opinion is that it is due to how our brain calculates (perceives) distance, with objects high ...
6
votes
2answers
1k views

What are the differences between matter, dark matter and antimatter?

I thought dark and anti matter were kinda the same, but after saw a video, they mention that dark matter is not antimatter but their explanation is a little fast so I got doubts. What are the ...
2
votes
1answer
127 views

Are stars really “burning balls of gas”?

Even the NASA website refers to stars as "big ball of gas". It's a common statement that's popularized by movies and popular culture. However, stars are technically not in a gaseous state - they're in ...
2
votes
4answers
126 views

Inclination in Kepler's laws

So, you can determine the location of an object in an orbit at any given time via Kepler's laws, but how do you determine the orbital inclination at any given point in time?
5
votes
2answers
297 views

Can I look at the sky and find the day of the week?

Suppose I wake up from a coma on a desert island in the 19th century (i.e. we already use the Gregorian calendar but have no satellites yet). I have a clear view of the sky and a couple of days to ...
5
votes
1answer
57 views

Why is Rosetta's Comet so “warm”?

Rosetta Comet AKA 67P/Churyumov–Gerasimenko has the surface temperature range of -43 to -93 degree Celsius. Now, if we compare that with the Mercury (I chose Mercury cause it's closest to the Sun ...
3
votes
1answer
75 views

How is the mass of solar system objects calculated?

When I go to the wikipedia page for any planet in our solar system, the exact mass and volume are reported. How is it possible to do this with them being so far away? I suppose after hundreds of years ...
0
votes
1answer
51 views

Observing a point 13.82b ly away, 1b years ago

I understand that we can observe far away galaxies to get an idea how the universe looked like in the past. Assuming the universe is 13.82b years old, would it be correct to say that if we looked at ...
-1
votes
0answers
33 views

How gravity bends light? [duplicate]

As light has no mass,how gravity effect it,even at such high velocity?
6
votes
1answer
44 views

When do Mercury/Venus reach greatest elevation at sunset/twilight for a given location?

On what day does Mercury reach its greatest elevation (in degrees from the horizon) at sunset a given location? The obvious answer is the day of Mercury's greatest elongation from the Sun, but, ...
0
votes
1answer
50 views

Identify this 2 axis motorized tripod

I am NOT an astronomy person, so this may be a dumb question, however I have recently found a tripod that appears to be for star tracking as far as I can guess. I would like to know the type of tripod ...
1
vote
0answers
44 views

Planetary reference systems and time

I am researching into how coordinate systems of solar systems objects are created by reading some of the reports written by the Working Group on Cartographic Coordinates and Rotational Elements (e.g. ...
1
vote
1answer
40 views

Seconds of Arc and the Unaided Eye

I've been presented with this problem: Say that Jupiter, with its diameter of 142,000 km, was located where Mars now orbits. What would be the angular size of (the newly-relocated) Jupiter ...
2
votes
3answers
130 views

Closest point on Earth to a planet?

I'd like to be able to find the latitude and longitude on Earth (assuming a sphere is fine) which is closest to Pluto at the current time (or where Pluto is directly overhead). Is this possible with ...
0
votes
1answer
88 views

Identify this object [closed]

I observed this when I was playing around with an amateur (crappy) telescope. The picture was taken using a dslr attached to the telescope. It was taken in San Francisco on 2015-01-20. I don't ...
1
vote
2answers
60 views

Delta-v from Mercury surface to Venus surface

What it says on the tin: using the most efficient launch opportunity afforded by orbital mechanics, what delta-v would you have to impart to a payload to send it from the surface of Mercury to crash ...
5
votes
1answer
170 views

How can one explain the apparent motion of the Sun from a heliocentric point of view?

From a horizontal frame of reference, the path of the Sun looks like a part of a circle in a tilted plane, as shown in this picture: ...
4
votes
1answer
83 views

How did Batygin estimate when Planet Nine was ejected?

Konstantin Batygin has estimated that if Planet Nine was ejected, it would have been ejected 3-10 million years after the formation of the Solar System. I'm curious as to how he arrived at this ...
1
vote
2answers
152 views

Will a Ball placed close to Sun fall into it?

Like a ball falls on the earth due to gravity, if suppose we are able to place a ball close enough to the sun. Will the ball fall into the sun due to its gravity or will it be pushed away due to its ...
4
votes
0answers
45 views

Oldest Reference to Astronomical Seeing

I'm writing a paper on astronomical seeing. Sir Isaac Newton identified both the phenomenon and origin of astronomical seeing in his Opticks. He writes: ...
1
vote
0answers
22 views

Public Data Set on Atmospheric Absorbtion / Extinction

Is there a publicly available data set for mean atmospheric absorption / extinction? I would like to be able to process and plot a graph similar to this image from NASA on wiki commons. The HITRAN ...
7
votes
1answer
88 views

Could the trajectories of non-periodic comets be used to infer properties of the 'ninth planet'?

Non-periodic comets are comets which have very long orbital periods (>200 years or more), spending most of their time in the outer solar system. Planet X, recently revived by researchers at Caltech, ...

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