# Tag Info

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 ...

18

The reason being closer to a heat source makes you warmer is the inverse square law. Think of it this way: If you have a $1~\mathrm{m}^2$ piece of material facing the Sun and located at Mercury's orbit, it will be quite hot. What does the shadow of this square look like at Earth's orbit (about $2.5$ times further away than Mercury)? Well, it will be $2.5$ ...

13

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 ...

11

Several points that need addressing: The seasons are due to the tilt of the Earth, but not because of the atmosphere. When the sunlight is grazing the ground at a low angle the same amount of heating is spread over a larger area than when the sun is directly overhead, so the temperature drops. The atmosphere has a negligible effect on absorbing radiation ...

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

The observable universe contains about 100 billion galaxies, each containing on average close to a trillion stars. That is a total of about $10^{23}$ stars. A typical star is like our sun. Sun has a mass of about $2×10^{30}$ kg, which equates to $10^{57}$ atoms of hydrogen per star. A total of $10^{23}$ stars containing $10^{57}$ atoms each gives us a total ...

10

Oh, but the edge of the atmopheres of Jupiter and Saturn (and the others) are fuzzy! Look at these Cassini images from a few years ago, at the CICLOPS website: "Adrift at Saturn" (PIA 07667), "Beyond the Limb" (PIA 10426), "Off Saturn's Shoulder" (PIA 09791) There is so much gas, such strong gravity, that it gets thicker and thicker quite rapidly as you ...

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 ...

9

which particular observation, made us think that it could be the other way around Retrograde motion must be a prime candidate. As seen from Earth against star background, Mars occasionally slows down and goes backwards. Our moon doesn't. It probably became clear to people constructing orreries that heliocentric models were enormously simpler and more ...

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

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 ...

8

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 ...

8

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 ...

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

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 ...

7

There's some excellent software called Celestia which lets you visualize constellations "from the outside" (among other things). You can easily tell, as you "move" farther away from the Earth, how the shape of the constellations changes. It's truly mind-expanding. They start to change "noticeably" if you go several light years from the solar system. ...

7

It is believed that the planets formed when a cloud of gas underwent gravitational collapse. Any small angular momentum that the cloud started out with has to be conserved, and since the cloud's moment of inertia becomes smaller, it spins faster. Also, the centrifugal force "throws out" the edges of the cloud and makes it more disc-like. As vartec said, ...

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 ...

6

You can get this from Newton's law of gravitation: the acceleration due to gravity is then $$g=\frac Fm =G\frac{mM_\odot }{mr^2}=\frac{GM_\odot}{r^2},$$ which comes out to about 5 mm/s$^2$. This is of course the orbital acceleration of Earth.

6

It would seem so, but there are a couple of subtleties involved. Firstly, if you time the rise and set of the sun everyday, and the rise and set of your favourite stellar constellation, you'll find that the constellation rises four minutes earlier and earlier everyday. This is easily explained if the Earth is revolving around the sun, but not so if the ...

6

The rings of Saturn should be visible in even the smallest telescope at 25x. A good 3-inch scope at 50x can show them as a separate structure detached on all sides from the ball of the planet. Source The best time to see the planet Saturn in 2013 will be in late April and May. Source

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 ...

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