# Tag Info

12

Just to put you at ease first, this is not an infantile question. 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 ...

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 ...

6

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 ...

4

I don't see any logical connection to accelerating expansion. If shrinking of galaxies could explain away the acceleration of the expansion, then it could also explain away the expansion itself. Regardless of whether we're talking about expansion or acceleration of expansion, the effect isn't measured by watching the apparent sizes of galaxies get smaller ...

4

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 ...

4

The effect that you're describing is extremely small. Have a look at the following figure: Here you see the position of the Sun from a location $L$ on Earth. Let's call $R_\oplus$ the radius of the Earth, $\Delta$ the distance between the Earth and the Sun, and $\varepsilon$ the obliquity of the Earth. The angle $\delta$ is the declination of the Sun at a ...

3

It seems to me that you have calculated the distance to the horizon rather than the altitude. The altitude would be $\frac{r}{\sin(60^\circ)} - r = r \times 0.1547 = 986\text{ km}$. Update: From within spacecraft the windows would restrict field of view, but in 1966 on gemini-11 mission Richard Gordon did a spacewalk at altitude of 1369km where the ...

3

There would be no effect on the image of Orion due to the obliquity of Earth. Keep in mind that the obliquity you've mentioned here is the angle of Earth's axial tilt with respect to the ecliptic. The angle of the ecliptic is relatively unchanging. While it may be true that certain locations on Earth we may see Orion shifted above or below our equatorial ...

3

How far away from earth's surface do we need to go to see its full hemispherical area? The strict mathematical answer is: no matter how far you go away from earth, you will never see its full hemisphere. So a better question is the one that generalizes your remark "I am interested to know how much of the earth you can see from the International Space ...

3

During daylight, you can only see the moon when the sun is fairly low in the sky and in the correct phase. For example, about 1 week after full moon you should be able to see it in the morning when the sun is not very high in the eastern sky. At that time, the 1/2 moon should be quite visible between vertically and into the western sky. Similarly, about 1 ...

2

No, the right ascension of the mean Sun is NOT zero at the vernal equinox. It is in fact nearly identical to the ecliptic longitude of the mean Sun (the difference is due to UT vs ephemeris time), and this is defined such that it coincides with the ecliptic longitude of the apparent Sun when the Earth is at perihelion. So that should be the starting time to ...

2

Someone outside a sphere, looking at the sphere, will always see a "full disk"! That's one of the properties of a sphere; it looks like a circle from every direction and distance . The two questions seem to be: 1) How large will that disk appear in the view of the person outside that sphere? Right now, I just looked straight down and noted that the ...

2

Astronomers know about this trouble, and stick with what they can measure. For distant galaxies, quasars, cosmic background radiation, etc. they use only the redshift, the "z" value. This is defined by the measured wavelength and the known laboratory value - assuming any spectral emission and absorption lines are correctly identified. To say anything about ...

1

First of all, galaxies don't shrink. If our own galaxy were shrinking, then we would be moving towards our galactic centre, and we would observe a blueshift in that direction. Second, the accelerated expansion can be determined from the relation between redshift and brightness of distant supernovae. Neither redshift nor brightness would be affected by ...

1

The difficulties are in some ways worse than you imagined and in other ways not as bad. The difficulties are worse in the sense that when we're dealing with distant galaxies, we need general relativity, not just special relativity. General relativity does not even have a well-defined notion of a global frame of reference, so it doesn't offer a uniquely ...

1

Aside from having Earth visible in the night sky instead of Mars, you would expect the same planets to be visible. Venus will appear as a bright star close to the sun - smaller than we see it, but still very bright. Jupiter and Saturn will be easier to see in the night sky, and it should be possible to pick out Jupiter's four major moons with the naked ...

1

For the layman interested in coordinates, go here and then click on the map link for any given day: http://curiosityrover.com/tracking/drivelog.html Then you're in the "Google Mars" view, with the rover's path displayed. Of course, you could figure out something to get a list of coordinates in a standard map format. But if you're looking for something ...

1

From Twitter: SPICE kernels for my location are available here http://naif.jpl.nasa.gov/naif/. For less technical locations, see https://foursquare.com/marscuriosity NASA is very open. For example, you can get more than 50,000 raw images from the Curiosity mission at the MSL website, and it's updated as they come in.

1

According to Thorne (Black Holes and Time Warps) all matter that approaches the black hole singularity is reduced to a common degenerate form - matter and anti-matter alike. The way I interpret it, matter ceases to retain any resemblance to what existed outside the black hole. The attributes that distinguish matter and anti-matter are stripped away. ...

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