# Tag Info

105

You are correct that the axis of the Earth's rotation is tilted with respect to the plane of its orbit by 23 degrees. But it is incorrect that the direction that the axis points changes by a large amount (it should be 2*23 degrees) over a 6 month time span. Your assumption: If axis it pointed at Polaris at (1), then it should be pointed at a different star ...

37

It depends on what object it's acting on. There are many objects, including stars, that have magnetic fields where Lorentz forces on charged particles like electrons and protons are stronger than the gravitational force on them. Also remember that the strength of the Lorentz force depends on the speed of the particle moving through it, so a fast enough ...

23

I feel sure this is a repeat, but couldn't immediately find it. The only things in the night sky we can see (with the naked eye) that are not part of our own Galaxy are (on a good night) the Andromeda galaxy and the Large and small Magellanic clouds. Every individual star brighter than $V=6$ and visible to the naked eye is in the Milky Way. So it would ...

18

It wouldn't be too apparent, but there are a few objects that you can see in good viewing conditions with the naked eye that would disappear. Here they are in order of brightness. I marked the objects in a reddish color. The Large Magellanic Cloud, apparent magnitude 0.9, located in the constellation Dorado. Only visible from the southern hemisphere. The ...

17

Let's look at the proper magnetic force (as opposed to the Lorentz force on a moving, charged object described in @KenG's answer) on a specimen $S$ of magnetized material with mass $M_S$ as a way to try to compare. Let's arbitrarily assume it has a fixed, permanent magnetic moment $m_S$. We can't use iron because it will saturate too easily. Then let's ...

16

Number of stars in the observable universe There are about 100 to 200 billion galaxies in the observable universe. Galaxies range in size from a few billion to hundreds of trillions stars. Using 100 billion galaxies and 1 trillion stars in a galaxy yields 1023 stars in the observable universe as a rough order of magnitude estimate. (After getting this result,...

14

Globular clusters occupy an interesting place in the spectrum of composite stellar systems. As you point out, they are highly concentrated populations of stars, and seem to lack any dark matter component, unlike more massive dwarf galaxies. Binary interactions become very important in simulating globular clusters, and interestingly enough (maybe ...

13

There is evidence from Silurian coral fossils that, 430 My ago, there were 420 daily rotations in each annual season, compared to 365 days per year now. If we assume that the year (fixed by mean Earth-Sun distance and Kepler's Laws) hasn't changed much in that interval, but that instead the day has gotten longer due to the Earth-Moon tidal interaction, that ...

12

Here is what I did: Based on their masses, it is safest to initially consider Jupiter and Saturn as well as Uranus. It might also be fruitful to include the Earth in the analysis, to get relative positions, observation angles, etc. So, I will be considering: Sun Earth Jupiter Saturn Uranus Neptune Get the standard gravitational parameters (μ) for all ...

11

File formats tend to be industry/field-specific, with the format, tools, and expectations of the field coevolving to become more dependent on each other over time. JPEG co-evolved with amateur digital photography, PNG co-evolved with the web. Likewise, FITS co-evolved with astronomical data processing, and so is naturally more suited for that purpose than ...

11

No liquid can be completely stable in a vacuum, since all liquids have some non-zero vapour pressure, and so will evaporate at some rate. However some liquids have an exceptionally low vapour pressure, and so can be used in a vacuum. The vapour pressure of silcone fluid DC705, which is used in diffusion pumps is 2.6e-8, and it is designed to function in a ...

9

Solar and lunar eclipses occur about equally often - between two and four times per year. However, when you do not intentionally travel around the world chasing solar eclipses, you are more likely to observe more lunar eclipses. The reason is that solar eclipses can only be observed from a comparatively small area while lunar eclipses can be observed from ...

9

Amateurs do useful scientific work by being many-handed and widely spread. Many Supernovae are discovered by amateurs. You need a set-up that can image one galaxy after another and look for any "new stars" that appear in them. As you are looking for the appearance of a Mag-14 star you need a big mirror; 90mm might not be enough. However look to Backyard ...

9

It isn't impossible, but the short answer is "no". A gravitational field will accelerate all matter and energy equally while a magnetic field will only accelerate moving electric charges (other magnets). The force due to gravity is proportional to the inverse square of the distance, and the force due to magnetism asymptotically approaches the inverse cube ...

8

You can not check if a dimensional constant has changed because you can always reverse that change by a smart change of coordinates (system of units). Despite that, since the current Physics assumes the immutability of certain constants, you can verify this assumption by testing the change of an adimensional constant. One of the most common adimensional ...

7

I personally found Stephen Hawking's "A Breif History of Time" to be very interesting and informative. It is a little bit advanced, but is put forward in plain English. Here is a link to it on Amazon, and you can "look inside" to see part of the book and see what you think. http://www.amazon.com/gp/product/0553380168/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=...

7

In fact, some people had looked at it more seriously recently and conducted a computer simulation to visualize the night sky as seen from within a globular cluster. The article has appeared recently in Astronomy journal. This is just one example of a typical image inside a globular cluster: Some more discussion can be found here: http://io9.com/what-the-...

7

It all comes down to the brightness of objects (not their size). For all intents and purposes we can assume that the most distant galaxies and the small, but much closer, objects in the Oort clouds are unresolved point sources.The Oort cloud objects are too faint to see, with JWST, but it should be able to see bright galaxies and quasars even at 13 billion ...

7

Light that is not light That's meaningless. All light is electromagnetic radiation. A finite part of the infinitely large range of the electromagnetic spectrum is visible light. So you should talk about EM radiation and to discuss the visible spectrum just say visible spectrum. Stars emit lots of energy at frequencies that are outside the visible range. ...

7

Seems a little contrived, essentially you just have to dig deep enough to find a specific enough category that matches the letter. But here you go : K - KBO (Kuiper Belt Object) , if you still don't like that you could use K - Kreutz Sungrazer (A type of comet, https://en.wikipedia.org/wiki/Kreutz_sungrazer) T - T-Tauri Star (A type of variable star, ...

7

There is no specific answer to this -- anything from "just sits there" to flys away at high speed is possible. It all depends on the symmetry of the supernova (SN) explosion. Extensive modelling shows that the explosions can be quite asymmetrical, and if they are the gravitational waves created can give the new black hole (BH) quite a kick. If the ...

7

The hours show the lines of right ascension, where right ascension is one of two coordinates used to specify a point on the sky. (The other coordinate is declination, measured in degrees from the celestial equator.) Right ascension and declination are similar to longitude and latitude on the Earth. The month and day show the right ascension of the Sun on a ...

7

I am Tomás the guy that designed it following astrocartography traditions. The thing that makes it confusing is that the position of the little suns in the Ecliptic are plotted against the stars at 12 noon GMT each day (the ephemeris) meaning that the stars behind it are NOT visible because of the sunlight. The stars that are visible at 12 midnight (...

7

I'd say your problem is that you are imagining the light rays emanating out from the center of the star. Try it again with light emanating from each square area on the surface, and you will see that being at the same temperature means each square on the surface sends out the same number of rays, but there are just more such squares. Then you will see a lot ...

6

In a typical position in a globular cluster (maybe halfway between center and edge), there'd be many more bright stars in the sky due to the star density. These would be distributed unevenly in the sky, with more light coming from the center of the globular cluster. Depending on the globular cluster's orbit, we might be able to see the Milky Way face-on. ...

6

The synodic month is the "average period of the Moon's revolution with respect to the line joining the Sun and Earth". However, the Earth also moves in its orbit around the Sun during this month. From our vantage point, the Sun has appeared to move in the sky with respect to the background stars, in the same direction as the Moon moves in the sky with ...

6

Throughout man's history, we have been learning things about the universe we live in. Probably one of the most interesting discoveries that let us know how amazingly large the universe really is was not really very long ago, only in the 1920s when Edwin Hubble demonstrated that the Milky Way was not in fact the total sum of the universe, but just a galaxy, ...

6

"The worldwide community of professional astronomers is only about 10,000; most are located in the us (with about 1,000 in the UK and 250 in Australia)." From So You Want to Be an Astronomer by Duncan Forbes. Another source stated that the number of professional astronomers is about the size of a small town.

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I know that quoting Wikipedia is frowned upon here, but as there has been no other answer posted, this is what the Wikipedia article on Kepler has to say about the matter: He then set about calculating the entire orbit of Mars, using the geometrical rate law and assuming an egg-shaped ovoid orbit. After approximately 40 failed attempts, in early 1605 he ...

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