# All Questions

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### Does liquid water on Mars means life?

We need to figure if liquid water is present throughout a Mars year, and how long the planet has been at its current distance from Sun. That will give us the length of time that liquid water has been ...
300 views

### What would happen if we stepped on the Sun?

I mean in intrinsic detail. What would happen to our bodies besides "burst into flames"?
53 views

### Is liquid water on Mars such a big leap compared with ice?

I thought we have found bacteria or other kinds of life on Mars. Now it is liquid water. Is there such a big difference between liquid water and iced water?
295 views

### Could there be dark matter black holes?

Could dark matter compress and form black holes? Since dark matter is even more abundant than normal matter, a dark matter black hole should not be rare...right?
145 views

### Are planets moving away from the sun?

I saw on the tv show Through the Wormhole (hosted by Morgan Freeman) that the planets in our solar system have been continuously moving away from the sun for millions of years. however, when I try to ...
91 views

### What is the brightest star (relative magnitude) in M31?

I am wondering what the brightest individual star is in M31, the Andromeda Galaxy. Specifically, brightest as seen from Earth (so relative magnitude).
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### Estimation of average rock and asteroid mass associated with different stars

There is a lot of information on different star types and compositions. Can we make estimates of the total mass of rock, ice, and non stellar matter that orbits stars based on star evolution models? ...
71 views

### What are the most valuable meteorites and asteroids in terms of precious metals?

There were some suggestions that asteroids could one day be mined for precious metals. I have found an outdated study that says that some siderites contain as much as 0.001% of gold: ...
171 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: ...
65 views

### Can all areas on Earth experience a total solar eclipse?

A solar eclipse only puts part of Earth at a time in shadow, so I'm not talking about a solar eclipse that casts a shadow over all of Earth. What I mean is: are there any areas on Earth where, no ...
95 views

### What light source can cause a shadow of a cloud onto the next cloud above?

Scenario- -Time & Environment-11:00pm Super Moon small town population 40,000 in Central Ca. -Nearest body of water is 80 miles away 4 small lakes of about 1 mile in diameter. -Pacific Ocean is ...
132 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 ...
117 views

### Is our Universe a hologram? [closed]

I watched a documentary where I heard some very strange theories that are difficult for me to comprehend. It is even difficult for me to explain what I heard. "Objects that fall into a black hole ...
46 views

### Gaia: What is the difference between CCDs used for astrometry, photometry, and spectroscopy?

My knowledge of CCDs is that these are sensors which collect photoelectrons. That's about it. What is a difference between CCDs used for astrometry, spectroscopy, and photometry? As an example, each ...
129 views

### Can we draw a min(distance) and max(mass) relation based on current observation data of nearby astronomical objects within several parcsecs?

The data precision now can exclude a >>$1M_{\odot}$ black hole, which has a , say 10000 year orbital period with our sun? We can draw a two dimensional diagram(Mass VS. distance) to show the region ...
70 views

### September 26 twelve hours sunrise to sunset?

I noticed in today's newspaper (Boston Globe, September 26) that sunrise and sunset were both at 6:25. That's the twelve hour day I'd have expected at the equinox. (Please retag if there's a better ...
177 views

### Less stars in the night, compared to 15-20 years back

I am not sure if my question is true or not. But this is what I observe regularly. When I was young and when I look at the sky, there were too many many stars were there. But now, from few months I'm ...
158 views

### Should a station in orbit around the Sun travel in the same or the opposite direction to the planets?

If we put a station in orbit around the Sun, and wanted to send transports as regularly as possible without the travel costs being prohibiting; should we have it rotate around the Sun clockwise, or ...
113 views

### Was there ever a Jupiter transit or Saturn transit?

I've watched the Venus transit 2004 with a small telescope, a relatively rare event, considering most people can only observe two in their life time. If E.T. were sitting in a sunny place on a moon ...
63 views

### Spheres in space [duplicate]

I know that gravity will turn a mass into a sphere, which is why planets and stars are that shape. But then we have asteroids and small moons which are not spherical. Such as a couple of Pluto's ...
32 views

### What visual artifacts are expected from the JWST?

What visual artifacts should we expect from the images that will be released from the James Webb Space Telescope? Specifically, do we expect 3-pronged diffraction spikes (any preview how they would ...
79 views

### Understanding Earth Tilt, Sun's Position and Lattitude Calculation

I've been trying to figure out how to calculate the latitude of my location with just the shadow of a stick cast by the sun. I am doing this under the assumption that I am stranded in some place with ...
78 views

### How does light so travel so fast?. [duplicate]

I've read that photon's have zero mass, hence no force is needed to accelerate them. But then the second question. How can gravity affect something which has 0 mass?. Yes, gravity(black hole) can bend ...
113 views

### Could an impact have resurfaced Venus 300 million years ago?

Venus surface isn't older than about 300 million years. The only explanation I've come across is that some kind of global volcanism resurfaced the planet. But couldn't it have been an impact event? A ...
27 views

### Stratospheric Balloon with an Xray camera

Some colleagues and I were planning to launch a stratospheric balloon in December. A thought occurred to me: what if we were to put some sort of xray camera in the payload? We are expecting a maximum ...
97 views

### What is the format of the data from the JPL's HORIZONS system?

I'm looking for accurate positions and velocities of the planets in the solar system over several decades. I want to simulate their trajectories using Newtonian laws of motion, and compare the ...
38 views

### LIfe without an ocean floor on an ocean planet?

Theoretically, wouldn't life need some sort of an ocean floor with irregularities where organic "soups" could "condense"? What about "membranes"? Don't theories suggest that if life came to be near ...
20 views

### Biosignatures for anaerobic or other early microbiology?

What are some possible atmospheric bio-signatures for a planet with anaerobic life? or even microorganisms before oxygen builds up in the atmosphere? Would there be a way of telling if methane, etc. ...
144 views

### When will Sirius be closest to the solar system?

Sirius is currently approaching the solar system, at a rate of 5.5 km/s, consequently in the future it will be closer and therefore brighter. When will Sirius pass closest to the solar system? How far ...
75 views

### Can we know where (South, East, West…) the moon will be at a specific time?

Apparently, a few nights from now (more specifically on the night between the 27th and 28th of September this year, nights being Belgian nights), we will have a lunar eclipse. That's great, and I ...
746 views

### What causes the antipodal bulge?

The Wikipedia article on tides shows a diagram with a tidal bulge both towards the Moon and on the antipodal point (the Sun isn't included in the diagram). Surely that's wrong - what would cause the ...
203 views

### Does any iron fuse in stars before they go supernova?

I understand that iron and all heavier elements consume more energy to produce than they make, and that is what eventually leads to a supernova. I also understand that a lot of the heavier elements ...
87 views

### How to scale down solar system data to simulatable values

Okay, I am seriously ashamed for asking this especialy when I geniualy study on physics but there is something that bugs me with the simulation I am working on. I am re-creating the solar system in ...
50 views

### Universal point for sky observation

Is there a place on Earth, where polar axis lies on the horizont and heaven equator is in zenit? If it exists, can I, in theory, see all the constelations available worldwide this night?
52 views

### Identification of Lunar mare (maria) from a taken picture

I'm in Brisbane right now. I took this picture 15 minutes ago from my balcony. Could you help me with identification of marked Lunar maria? I cannot compare any of these to this map. I think 1 is ...
247 views

### How Do we know about redshift?

Okay so scientists use the red shift to know that galaxies are moving away from us faster than light. How do we know that its not just red light from red stars. i mean most stars are in the infrared ...
230 views

### Where exactly does the Moon flip, given that it appears the other way up in the other hemisphere?

I've read in multiple sources that the Moon appears the other way up in Northern Hemisphere vs Southern Hemisphere. Here is one that explains why: Does the Moon look different in the northern and ...
31 views

### If we pumped an large EMP into High Earth orbit and it detinated would it act as a shield against solar radiation?

Could this pulse potentially shield spacecraft from harmful solar radiation. I was assuming an EMP would have little effect as a radiation shield because the pulse would not be rapid enough to ...
67 views

### Ocean floors on ocean planets?

I know that models of ocean planets typically have deep liquid water that transitions into exotic forms of ice. What I am wondering is if it makes sense to have an "ocean floor" composed of debris ...
61 views

### When is the belt of Orion slanted from right to left, going up? (Egypt)

I am trying to match up a detail of the Senemut ceiling to the time of the year it might involve. In the detail (shown below), the belt of Orion is slanted upwards from right to left: Notice that ...
686 views

### two black holes orbiting each other within their event horizon

Is there any argument against this situation: two black holes, one within the event horizon of the other, and the system is stable. It is interesting to me because that if this works, we could have ...
112 views

### What is the angle between the equator of the sun, and the plane of the Earth's orbit

I want to know the angle between the plane that passes through the centre of sun and is perpendicular to its spin axis, and the plane that contains the orbit of earth around sun? Is this a fixed ...
150 views

### How many satellites orbit the Earth? At what rate do they orbit the earth? [closed]

I was looking at a full moon the other night with my telescope and noticed a black dot move across the moon quite rapidly. This happened a few times and others who were with me were able to confirm. ...
2k views

### How can we avoid needing a leap year/second?

Given the Earth's current speed around the sun and current rate & axis of rotation, what is the best way to keep time to avoid a leap year? How many hours should we have in the day and days in a ...
100 views

### Why you use log to measure metallicity in galaxies?

For example, I saw the next expression for matallicity in a paper: $\log(O/H) + 12$. I understand O/H is the O(Oxygen) to H(Hydrogen) ratio but why is there the number 12? And why the logarithm?
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### The battle over Gliese 581 and Gliese 667C?

In 2014, Robertson et.al. made a case that stellar activity is masquerading as planets (here and here) for these well known systems. In both cases, they claim that the only real planets discovered so ...
138 views

### If an Asteroid was to strike the Earth, would it affect the Earth's rotation?

If an Asteroid was to strike the Earth, would it affect noticeably the Earth's rotation, and if so, how large would this Asteroid have to be?
121 views

### Is any consensus forming on the solution to the “Lithium Problem”?

The "Lithium Problem" relates to the fact very-low-metallicity stars appear to have a Li/H ratio approximately one third of what would be expected. The ratio should be the same as the prediction from ...