# All Questions

49 views

### How many stars can be seen naked eye from outside the atmosphere? Ho dense is the “sky” from there?

When I was 20, I went to Naxos (Greece) with friends. I was driving my car during the night on the mount Zeus (1003 meters - 3,291 ft) listening Pink Floyd. Up there we stopped the car to take a ...
255 views

### Distance between Earth and where The Big Bang's happened? [duplicate]

The universe is around 13.8 billion years old. We know how fast the light is. We also know how fast our galaxy moving around inside observable universe. Is it possible to calculating distance ...
131 views

### Could the Philae comet lander be recharged by laser?

Could the Philae comet lander be recharged with a laser (or possibly many lasers) from earth? My thought would be to aim one or more powerful lasers from earth at the Philae lander to recharge it ...
78 views

### Are our 'observations' of or near a black hole affected by gravity induced time dilation?

This answer made me wonder if matter/energy/events near a black hole are viewed (by us) in a very different time frame, how might that affect our measurements? ...
182 views

### Can the theory of multiuniverse explain dark matter?

If there are many universes they must have an gravity effect on each other. Since dark matter is measured through gravity but we dont know the mass behind it, isnt it possible that it comes from ...
89 views

### What it would look like to observe people with a different time flows?

As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks. So Imagine two different ...
5k views

### How does the Earth move in the sky as seen from the Moon?

I just want to be sure I am visualizing this correctly, because it seems odd. The Moon is tidally locked to the Earth but there are wobbles to its motion due to libration. So from a point on the ...
223 views

### Why does the distance between Sun and Earth stay the same?

Well, we all know Sun gravity , makes the Space time curvature and space pushes the earth towards the Sun. But my question is "why the distance between the Sun and Earth is Same? Earth should have ...
93 views

### How can astronomers determine the difference between “hydrostatic equilibruim” and “just happens to be spherical”?

This is relevant for the definition of a dwarf planet. I presume the answer will be, well, if we can tell the mass of the body and guess the material. I don't find this very satisfactory because ...
132 views

### What is the long term fate of the gas giants?

If I'm not mistaken, it is believed that the reason for such turbulent weather on the 4 outer gas giant planets is that the internal pressure is so great that it is generating heat, which is causing ...
143 views

### What are the nearest galaxies I can observe?

What are the nearest galaxies I can observe using my Telescope? Does it require to be out of the city lights?
71 views

### Free neutrons and stellar nucleosynthesis

Both the R-process and the S-process of stellar nucleosynthesis rely on absorbing 1 (S) or more (R) neutrons. Where do they come from? I thought there are no free neutrons in stars. (Also the ...
95 views

### Have we detected galaxies which have red-shifted beyond the visible light range?

According to this answer it is possible for galaxies' light to move beyond the visible frequencies due to redshift: ...
154 views

### Without using absolute magnitudes or isochrones, how might we tell a star's age and evolutionary status?

Usual methods of estimating stellar ages involve isochrone approximations. It can also help to estimate a star's radius by correlating its absolute magnitude with effective temperature and apparent ...
87 views

### What is the reason for high lithium concentrations in Sun-like stars?

In reading the European Space Organisation paper Lithium depletion in solar-like stars: no planet connection (Baumann et al. 2010), several conclusions based on their observations include: Lithium ...
842 views

### Why can I see the whole moon during various non-full-moon phases?

Here's an image that describes the phenomenon I'm asking about. The very thin sliver to the left is of course the surface of the moon as lighted by the sun. But the rest of the moon is also faintly ...
60 views

### Red shifting galaxies

I am an amateur astronomer please correct if any of my understandings are wrong. We all know that from the Hubble's ultra deep field image the most distant galaxies which were created shortly after ...
53 views

### How do I find the RA of sunset and sunrise in a specific location?

I want to make some observations with a telescope in Hawaii on Mauna Kea but I am living somewhere else (not Hawaii) and I want to plan a night's viewing on the Hawaiian telescope. How do I find the ...
130 views

### Maximum Amplitude of a Lissajous Orbiting Object in a L4 or L5 Position

I stumbled on The Lagrangian points during some wikipedia reading. After looking at the gravity contours, I naturally come to the conclusion that the L4 & L5 should have a wave pattern and then ...
141 views

I'd like to one day take the Astronomy Olympiad, however I'm at a loss to know where to begin. As it currently stands I have no experience whatsoever with Astronomy. If there are people here with some ...
17 views

### Where can I find historic rates of meteor impact events?

I have a friend that watches a lot of TV news and they have the impression that impact events are becoming more common than in recent memory. Does the evidence support or refute this? Thinking it ...
215 views

### time on earth compared to completely stationary in space

I recently started trying to understand the theory of relativity and I have the following question. Because earth is orbiting the sun at approx 67,000 mph (and its my understanding time slows down ...
23 views

### In the chromoscope, what is the X-ray source between Ophiuchus, Libra and Scorpius?

http://www.chromoscope.net/ is a nice toy. Pressing 'L' shows the constellations as guide. There's a bright X-ray source between Ophiuchus, Libra and Scorpius. In Hydrogen-Alpha there are two ...
101 views

### Why isn't the moon dark in a solar eclipse?

In the following partial solar eclipse, the moon is "invisible" rather than being dark. By contrast, if someone stands between my view and the sun, they will appear as a dark figure instead of ...
106 views

### What is “Median Stellar Mass”?

Could someone explain what is "median stellar mass" and how is it calculated? I have seen it written as: $$\log(M)$$ or as: $$\log\left(\frac{M_*}{M_{\text{Sun}}}\right)$$ but I do not ...
120 views

### What are the last images from the Galileo orbiter before impacting Jupiter?

NASA's Galileo orbiter at Jupiter ended its mission in 2003 by intentionally dive into the gas planet. Did it take and transmit any close up images before it ceased to function? If not, why? Are there ...
63 views

### Where can I learn these Astrophysical techniques? [Read below]

Whenever I read any Astro papers in http://arxiv.org/ they usually talk about Data fitting or modelling or sentences like 'we fitted the spectral region by analytic functions i.e. by multi-component ...
36 views

### What is the cause of the variation from high and low mean obliquity periods of Mars?

It is reasonably well known that Mars has a greater obliquity range than Earth, due to Mars lacking a stabilising influence of a large moon. However, the Martian obliquity seems to have gone through ...
30 views

### How tall are the “fractured” linear structures on Europa's surface?

What are the altitude differences in the high resolution part of this image of Europa? How high do those ridges rise over their neighboring valleys? And how large is the area shown in this image? ...
149 views

### How do you calculate the effects of precession on elliptical orbits?

Kepler's first law states that planets (and all celestial bodies orbiting another body) travel in elliptical orbits, which have well-known formulas that make it relatively easy to calculate the ...
65 views

### Is the location that published calendars use to calculate the seasons one specific location on the earth?

All the calendars in my house say the fall equinox is Tuesday the 23rd. All the astronomical programs and astronomical sources say it is it is Monday the 22nd in Ohio. Since the time given is 10:29 ...
298 views

### Hulse Taylor Binary Pulsar - How is “Cumulative Periastron Time shift” calculated?

Following on from a previous question about the interesting Hulse Taylor Binary Pulsar. BACKGROUD Weisberg & Taylor, 2004 present a graph showing the change in "Cumulative Periastron Time Shift" ...
46 views

### speed of light measurement

While searching for different methods of speed of light measurement, i came across one of the method of fizeau discussed below which i cannot fully understand. In short,in Fizeau’s apparatus, a beam ...
178 views

### Why does the face of the moon 'sync' with the earth? [duplicate]

We never see the dark side of the moon. It rotates so that the same side always faces us. I heard two (dinner party) theories on this: 1. The moon was made by smashing out a chunk of the earth, and ...
515 views

### How likely and severe is the threat of a gamma ray burst to earth?

In the National Geographic article: http://news.nationalgeographic.com/news/2009/04/090403-gamma-ray-extinction_2.html it is suggested that a gamma ray burst likely caused a mass extinction in earth's ...
267 views

### Planets and Pluto? Neptune?

If one of the rules to be a planet is that it needs to clear ALL objects from their orbit, does this also make Neptune a non-planet? Since it has thus far failed to clear Pluto (and based on an answer ...
40 views

### How is the maximum density in a circumstellar disk determined?

I'm working with some equations to model the evolution of a circumstellar disk. One of the equations is $$\rho(r)=Ce^{-\frac{(r-r_{peak})^2}{2 \sigma ^2}}$$ where $\rho$ is density, $r$ is the ...
131 views

### Effect of the absence of atmospheric refraction to sun rise and sunset times

What is the effect of absence of atmospheric refraction on sin rise and sunset time? Is it will be delayed or earlier for sunrise and sunset, and why? Thank you:)
93 views

### How does this strategy for chasing the sunset work?

In Randall Munroe's What If? blog he tackles this question: What is the longest possible sunset you can experience while driving, assuming we are obeying the speed limit and driving on paved ...
157 views

### What is a low mass Black Hole?

Is a Low Mass Black Hole also called a Stellar Mass Black Hole? Can Low Mass BH be also called Primordial BH? (If low mass BH are Stellar Mass BH-What is their size in terms of the mass of the sun?)
142 views

### Detecting Deep Impact

There have been several accounts in media articles of asteroid near misses, many describe that the asteroid was not seen before the near miss. After reading the question and answer to How can we tell ...
112 views

### How does 67P rotate?

What can be said about 67P/Churyumov-Gerasimenko axial tilt? Is it fixed (if so, at what value), only changing with precession (at what rate?) or does 67P "tumble" with axial tilt changing over time? ...
109 views

### can we see all binary stars as pairs?

As it is obvious from the question title is there any restriction or cases that we can see the binary stars as not in pairs also is there any binary stars doesn't linked together by gravity ? I ...
50 views

### Roche Limit for Earth-like body around Earth-like body

In a discussion elsewhere about binary planets, it came the question. How near can a planet like Earth (maybe Earth itself) be to another planet like Earth before both of them tearing apart due to ...
121 views

### How can there be anything “beyond” the CMB?

Two things we take, for this purpose, to be axiomatic: The CMB is the oldest thing we can observe directly The cosmological red shift tells us how "old" something we are observing is Yet we also ...
58 views

### Determining Distances in Space [closed]

I suspect the scope of this question may be to broad, but: what are some methods for determining distances between two objects in Space? Please present the methods in historical order, so as to make ...
89 views

### Why does Earth enjoy a significantly longer time as a habitable planet as compared to Mars or Venus? [closed]

On a related note, why didn't Venus remain habitable for longer than it did? Is the current hypothesis as to the time when Venus's atmosphere became hostile and what event triggered it, proven true?
119 views

### Appearance (frequency) ranking of stars?

Is there some ranking / statistics that shows how common given type of celestial objects is? A table that would allow the answers to questions like: What type of star is most common per volume of our ...