Hot answers tagged observational-astronomy
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@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 ...
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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 ...
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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 ...
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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 ...
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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.
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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 ...
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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 ...
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What Water and Peter have mentioned is correct -- and the Balmer-alpha line (aka H-alpha) is the main spectral line that ground-based solar observatories observe, if they're not using a broad filter.
... but you're not going to see a lot of prominences, as they're more commonly associated with the transition region ... and for that, you're going to need ...
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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 ...
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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 ...
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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, ...
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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 ...
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The first step to observing a lunar eclipse is to make sure that it's visible from your location. This is most easily done with NASA's lunar eclipse page. Look for the calendar date that you're interested in for the eclipse, and then you can get a broad idea of what regions of the world it will be visible in. You can click the link of the calendar date to ...
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Yes, with a relatively inexpensive solar filter in front of the telescope almost any telescope can be used. The solar filter can be based on BoPET (trade name "Mylar").
To view flares and prominences a much more expensive (on the order of USD 1000 for a 8" reflector) hydrogen-alpha filter is needed.
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If you want to project the image of the sun onto a screen, you don't even need (or want) a solar filter. To do this you place a screen a good ways behind the eyepiece and focus the image onto the screen. This works best if the image is not directly behind the telescope as it will be washed out by the direct sunlight.
The exact distance depends on the ...
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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 ...
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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 ...
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Absolutely not. Even though a laser beam is very narrow, it does spread out, and by the time it reaches the moon it will be a couple of hundred meters wide. The moon is not very reflective (with an albedo it only reflects 1/8th of the light falling on it). Thet reflected light is spread out further by the roughness of the lunar surface so that, by the time ...
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You may use mylar filters in front of the telescope, as other said. Another common way is to add a green glass filter at the entrance of the eyepiece (normally screwed in). This solution is normally shipped with the telescope, but I highly recommend against it. The reason is that the glass may crack due to the heat, which may compromise your retina if you ...
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An HBTI works in a very similar manner to a Fizeau / Michelson stellar interferometer. But in an HBTI, a correlation is made between fluctuations of amplitude (intensity) at points across a surface, unlike a Fizeau/Michelson which correlates fluctuations in phase. The timing of these fluctuations is much longer and this leads to a much larger tolerance in ...
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The Earth is 1AU from the sun (by definition!) so the sun is only 1/122 of the diameter in Voyagers sky. That means it would appear as large as stars appear to us on Earth by eye.
The light from the sun though spreads out with the area of the sphere, so the square of the distance. This means that at voyager it is only 1/(122*122) = 0.007% as bright.
Thats ...
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We do have space telescopes (COBE, WMAP, Planck) that operate in the microwave region, and indeed they do see much, much deeper into the universe than HST. The Hubble Extreme Deep Field renders images of a universe that is a few hundred millions of years old. In contrast, COBE, WMAP and Planck provide us with a view on a 0.37 million years old universe.
...
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It depends on the constellation or the galaxy considered:
The closest visible star is Proxima Centauri at around 4 l.y.
source
The furthest visible star is possibly Rho Cassiopeiae at around 8,100 l.y.
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The closest visible galaxy is the Andromeda Galaxy (M33), at 2,540,000 l.y.
source
The furthest visible galaxy is maybe Bode's Galaxy (M81), ...
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