Tag Info

Hot answers tagged

13

@dmckee guessed correctly. From An excerpt from an address delivered before Section A of the American Association for the Advancement of Science, on August 23, 1882, by Prof. Win. Harkness, Chairman of the Section, and Vice President of the Association: (ref) He was destitute of what would now be regarded as the commonest instruments. The invention of ...


12

What you're seeing is the galactic plane of the Milky Way. There are several processes emitting at a variety of wavelengths, and because the emission is so nearby it comes out quite bright on the all sky map. Planck observes at about $\mathrm{mm}$ wavelengths, so the most prominent emission within the galaxy is thermal emission from dust clouds. Often maps ...


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

Here is a nice answer, taken from http://www.enchantedlearning.com/subjects/astronomy/stars/twinkle.shtml The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation). Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's ...


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

In most cases you are right, stars are pointlike. They are spread over multiple pixels not because of charge overflow (this can be overcome with shorter exposures and/or better equipment; there really should never be overflow in the image) but because the point spread function (PSF) of the telescope is larger than a single pixel (which is a good thing; you ...


10

The most compelling evidence of GR in presence of matter is, in my opinion, in neutron stars. These objects have a surface gravity $SG$ that is (geometric units): $SG_{NS}=GM/c^2 R \simeq 0.1 $ This value is telling us that we can't use Newtonian gravity because we are in the strong field limit. For comparison, the sun has $SG_{SUN}=GM/c^2 R \simeq 10^{-5} ...


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 transits of 1761 and 1769 were used to determine the size of the solar system through parallax and Kepler's third law. By the 17th century, astronomers could calculate planets' relative distance to the Sun through the Earth's distance (AU), but they had no accurate measure of the absolute distance. Precise times of transit of Venus across the solar disk ...


8

Maybe. The Galilean moons are (barely) bright enough to be seen with the naked eye, but they're so close to the much brighter Jupiter that seeing them is at best very difficult (but easy with even low-powered binoculars). Jupiter is not currently at opposition (the closest it gets to Earth), so that's not ideal. I've never seen them without binoculars or ...


8

The curvature of the universe can be derived from the temperature fluctuations in the Cosmic Microwave Background. For a given amount of radiation, baryons, dark matter and dark energy in the universe, these temperature fluctuations can be calculated theoretically, and compared with observations, and so one searches for the values that yield the ...


7

One point doesn't tell you much of anything, other than that there is probably something in that direction. Pluto was discovered the same way many asteroids are, by comparing pictures of the same star field at different times, seeing if anything changes. Below is the discovery image from Wikipedia. The dot moved across the image, while all the stars ...


7

Tapering makes no difference in Snell's law. If you have a refractive index profile n(z) [approximately independent of x and y], and you know the angle of the light at z1, then you can figure out the angle at another point z2 using Snell's law -- and the angle only depends on n(z1) and n(z2), not n(z) for any other z. It doesn't matter how smooth or sharp ...


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

The vertical arch runs from due North to due South, thus dividing the sky into Eastern and Western hemispheres. The imaginary line in the sky it traces is called the Local Meridian. This can be used as a crude sort of timepiece- the time that the Sun crosses it is your local solar noon. The particular time that other objects cross that arch is called the ...


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. ...


6

The sun would be similar in size as to many other fuzzy point-like stars in the sky. Its luminosity is pretty low at such a distance (about 122 Earth-sun distance). As Martin says, it is indeed a moon-light view. This image is more or less similar to the 122 AU view. Thanks to Celestia (an amazing environment where I wonder about space) for this wonderful ...


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

In general, more glass means the image gets worse. However, if the barlow is good, the losses and aberrations are below the annoyance threshold or, rarely, below even the perceptual threshold. It's all in the eye of the beholder anyway. Also, especially with cheaper eyepieces, it is sometimes the case that the more powerful eyepieces have less eye relief, ...


6

The Milky Way has prominent dust lanes that can obscure a significant portion of it. As seen in the various pictures in this article, there are parts where the dust lanes are so thick that it might actually appear to be two bands. I used to teach an astronomy lab where plastic celestial spheres (like world globes, but for the sky) were used. They had the ...


6

You were likely seeing what's called "The Great Rift" in the Milky Way, which is not a void in the Milky Way, but rather a cloud of dust that's "only" about 300 light-years away, and thus obscures vast numbers of stars. Last night, from Australia, it would have been very prominent in the NE in the evening sky. It's also possible that you saw the Magellanic ...


6

There was significant luck involved with this detection to be sure, but it doesn't involve either the figure of 3.8 billion years, or with happening to have our instruments pointed in the right direction. We were lucky that Earth happened to be sitting directly in the path of a very narrow beam of radiation emitted by this event. The third image on the page ...


6

Well, First off, you can see the Andromeda galaxy with your naked eye from a dark place on a clear night. You should try it if you can. It looks like a smudge of appreciable size, not like a point. So half way between the Milky way and Andromeda, both would look like smudges twice as wide as Andromeda does from earth. I think a standard point and shoot ...


6

One big discovery since the 2004 transit is all the transiting exoplanets seen with Kepler, including some the size of Venus. The great thing about transits is the potential for measuring the chemical abundances of the planet's atmosphere with spectroscopy. Of course, the sun give us a way of testing this in the extreme limit of nearly infinite ...



Only top voted, non community-wiki answers of a minimum length are eligible