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21

First, the speed of other galaxies isn't too helpful. For example, the radial velocity of the Andromeda galaxy relatively to us is 300 km/s, i.e. 0.1% of the speed of light only. Moreover, internally, everything in that galaxy moves by pretty much the same speed and is confined to the vicinity of that galaxy which makes us pretty sure that no piece will ...


20

Why don't we observe any relativistic asteroids? The answer to this question would not be complete without mentioning the virial theorem. Considering our galaxy as a system of $N$ gravitating objects, according to the virial theorem, twice the average total kinetic energy of all objects, plus the average total potential energy of these objects, adds up ...


14

No, there is not a solar eclipse whenever we see a new moon. The reason we do not have a solar eclipse at every new moon is mostly due to the angle of Earth's axis (and by extension, the Moon's orbital plane) to the Earth-Sun line. See the picture below for a visual explanation. In the picture, the Sun is to the left. The upper image shows the orbit of the ...


13

Great question. The electric field creates such a strong force that it would be very hard to move large amounts of just one type of charge. So astrophysical systems do generally eject equal numbers of protons and electrons. In particular, the solar wind is electrically neutral. So these cosmic rays are created in very nearly equal numbers, but by the ...


11

Short answer, no. The Sun's orbit is non-Keplarian; there are many perturbations and a general unevenness in the motion of the Sun around the Galactic centre. This is a result of non-uniform mass distributions, the galaxy not being a point mass, and the impact the relative motions of neighbour stars has on measuring. Thus, giving a particular eccentricity ...


11

Did you read the Wikipedia article? It explains the signal rather well, I think. At any rate, it is called the Wow! signal because, as the picture shows someone wrote Wow! in the margin. As for the code and why they were excited, I quote the Wikipedia article, The circled alphanumeric code 6EQUJ5 describes the intensity variation of the signal. A ...


10

First let's quantify what kind of resolution we have of Earth from the moon? This can be calculated. The distance (range) from the Earth to the moon is is $R_\text{EM} \approx384,400,000$ meters. The angular resolution of the human eye is $\theta_\text{eye}\approx.07^o \approx .0012 \text{ radians}$. The spatial resolution of the earth viewed by the ...


10

The angular resolution of a telescope is approximated by the formula: $$\sin \theta \approx\theta\approx1.220\frac{\lambda}{D}$$ So, if we know the angle, we can calculate the diameter $D$. The rest really depends on how big the flag is and where on moon it has been planted. Assuming 50$\text {cm}$ as the diameter of the flag, and assuming the flag is ...


10

Increasing the diameter and distance of the Moon by a factor 2 would lead to a number of very subtle differences. I will list the ones I came up with: Apparent size If $R_m$ is the radius of the Moon and $D_m$ its geocentric distance (that is, the distance between the centre of the Moon and the centre of the Earth), then its geocentric angular diameter is ...


9

Our two closest planetary neighbors -- Venus and Mars -- have no significant magnetic fields. In fact, the most recent numbers I know of for an Earth-like (dipole) field on Mars say that its strength as no more than 1/10000th the strength of Earth's. On the other hand, Jupiter's magnetic field is about 20000 times stronger than ours. There is no reason ...


9

The color of a star depends on its mass and temperature. The distribution of these also depends on the age of the galaxy. When the galaxy is very young, there are large amounts of gas still available for star formation, and many young, heavy, hot stars mean that the galaxy is very bright and shines in bluer light. This can be seen as an analogy of the quick ...


9

The number of stars that are visible depends heavily on local conditions. Under perfect conditions (e.g. a mountain area with minimal atmospheric turbulence) and with perfect eyesight, one would be able see stars as faint as magnitude 6.5. Of course, conditions are usually not ideal. According to this site, there are 1500 stars brighter than mag 5.0 4800 ...


9

You mean like Arthur C. Clarke's 2010 when Jupiter turns into a star? We often turn to Jupiter's mass ($M_j$) when thinking about this problem. It turns out there's a whole class of stars that fuse so faintly that we can only see them well in infrared. Brown dwarfs (which are still called "stars") turned out to be so cool that only new infrared ...


9

It is happening because of the acceleration of the Earth orbital speed around the Sun (Earth is near the perihelion). Between December 13 and December 31 the Earth is speeding up and also it is normally rotating around its axis. These 2 movements (constant rotation and increasing orbital speed) add up to create the observed apparent movement of the Sun on ...


9

Surprisingly it's quite easy to answer this because we can use the cosmic microwave background as a reference. The CMB gives us an average inertial frame for the universe so our motion relative to it is the closest we can come to defining the Solar System's motion through space. The CMB is isotropic, but because we are moving relative to it the radiation is ...


8

I feel that exactly the opposite should be the case; that is, dark matter halo should be inside the galaxy rather than outside. Your feeling is entirely correct, and actually agrees with dark matter theories. Your only mistake is in thinking that the dark matter halo of those theories is only surrounding the galaxy; it's also inside the galaxy, and is ...


8

The short answer is you can't, or at least not at all easily. Your detector has only a single detection plane, and almost all muons are minimum ionizing, so you get essentially the same energy deposition from every muon (well, there is a factor from the angle of incidence the detection plane). The usual mechanism for measuring the energy of a particle are ...


7

Believe it or not, the Moon was visible during the day in 1949. In fact, the Moon has always been visible during the day at certain parts of the lunar cycle. We know this is true not only because of models of the Earth-Moon system, but there is historical evidence of it! There are records dating back to ancient China in 2800 BCE of solar eclipses, which are ...


7

If the majority of the radiation emitted by a star is infrared, the majority of the visible light emitted will be red. We don't see the lower half of the spectrum the star emmits If the majority of the radiation emitted by a star is infrared but some is visible, the average visible light emitted will be yellow. Little blue is emmitted and any green ...


7

Stars Indeed, the most readily apparent observables for stars are (1) their apparent luminosities, and (2) their spectra (or even just colors if you can only do photometry). The age has to be inferred, and this is where modelling comes into play. The Vogt-Russell "theorem" is the assumption that the initial mass and chemical composition of a star uniquely ...


6

Gamma rays are very high energy electromagnetic radiation with very short wavelengths (on the order of picometers), which does make them remarkably well-suited to penetrate/pass through objects. Wikipedia provides a great description on all of the characteristics and applications of Gamma Rays. There are, in fact, many uses for Gamma rays in science already ...


6

A major part of the reason for this is due to the temperature of the ground. While the length of days in the Summer are effectively a mirror of those in Spring, you must take into consideration more than that. When Spring commences in temperate climates, it is (usually) immediately preceded by winter. Due to the Winter, the ground and/or surrounding bodies ...


6

While the chosen answer isn't incorrect it doesn't really answer the question -- that it isn't that rare on other planets. For a total eclipse you have to fall into the Umbra portion of the shadow. From this image you can see that the size of the moon and the distance from the sun as well all play an important role. If we look at the planets and moons ...


6

A galaxy spectrum is a quite complex and complicated topic, and many entire careers are fully devoted to understanding them, so this can only be a simplified answer. It is still quite lengthy, though, so if you're impatient, I've summarised it at the bottom. A blend of starlight of different spectral types makes up the continuum. The light is emitted by ...


6

There's actually at least one very big clue that's been accessible to skygazers since the earliest times: the first quarter moon at dusk. Every child in the northern hemisphere going back to 30,000 BCE likely would have been familiar with how 1st-quarter moons always tend to rise at noon, reach its highest point at sunset (with an azimuth directly south), ...


6

While most measurements in astronomy are better in space, precision spectroscopy can actually do quite well on the ground. One of the best spectrographs (some would say the best) is HARPS, the High-Accuracy Radial Velocity Planetary Searcher used for finding extrasolar planets. As described in its instrument paper (pdf; note that the sole purpose of this ...


6

It seems from the Nature paper that what we see is a temperature variation map with the darkest and the brightest regions representing a temperature difference of $\sim 10 \%$ of the mean temperature (remember, though, that by Wien's displacement law, temperature and brightness are connected, so in some sense it is also a brightness map). The ...


5

It's not easy to accurately determine the position of the Sun within the Galactic disk, but according to most studies, the Sun is located between 15 and 25 parsec above the Galactic midplane. You can find various estimates in the Introduction of this paper: http://arxiv.org/pdf/0704.0950v1. 1 parsec corresponds with 3.26 lightyears, so 20 parsec is about 65 ...



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