# Tag Info

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An arc spectrum is one produced by a discharge lamp where the discharge is through ionised gas, in the case of He-Ar a mixture of Helium and Argon, which produces a predictable line emission spectrum. They are often used to provide a calibration spectrum for spectrometers.

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I think your question covers a lot of ground cause you're asking it from 2 different perspectives. How were the orbits of planets first mapped out? and How do we know what position in space a planet will be at certain time so that spacecraft trips to planets could be planned etc. These should probably be separate questions, as they're quite ...

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The Astronomy Picture of the day for the 23rd November 2015 has all the neblosity around Orion, in fantatic detail. The result of 212 hour exposure.

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I wrote some JavaScript to help answer my question. It's in terrible shape right now, but it plots the hourly position of Aldebaran in azimuth & elevation when viewed from Dayton, Ohio, USA, every fortnight for a year: http://fasiha.github.io/starpath/ The source code is at https://github.com/fasiha/starpath but everything in it is hardcoded. However, ...

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You could use your image to estimate the angular size of Jupiter that night. To find the actual diameter of Jupiter you would also need to know the distance that Jupiter is from Earth, and since Jupiter and Earth are both orbiting the sun, this distance changes. You can find the distance with software (Eg Stellarium) or using Nasa's Horizons web interface ...

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In the Fall (early morning) and the Winter (early-late evening), Orion is a large an easily identifiable constellation. In the Spring (early morning) and the Summer (early-late evening), Cygnus and Pegasus are two large and easily identifiable constellations. Check out an application called Stellarium. It's free and available for every current platform ...

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I think what you want it for is all important? I use World Wide Telescope (http://www.worldwidetelescope.org) as a demonstration tool. You can use it to look at any part of the sky using a variety of catalogues and imagery. The default "background" imagery is from the digitised sky survey. The way it works is that if you zoom into an area it downloads ...

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Install either Stellarium or Cartes du Ciel, drag the sky chart around, zoom in or out, frame the constellation any way you like, then take a screenshot. http://www.stellarium.org/ http://www.ap-i.net/skychart/en/start

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It varies throughout the year. A book or a website with maps will help. In Spring, Leo and Boötes dominate the southern skies, with Coma Berencies between them In Summer, the summer triangle of Deneb, Altair and Vega is seen, with Cygnus flying along the Milky Way, and the rich star fields of Saggitarius closer to the horizon. In Autumn there is the ...

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The video is hilariously wrong. However, the principle of laser ranging is more or less right, and it does require the reflectors left behind by the astronauts on the Moon. It's just that the physics and technology involved are far beyond just pointing a toy laser at the Moon. Project APOLLO (Apache Point Observatory Lunar Laser-ranging Operation) is ...

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Neither of these seem correct to me. You are correct. The Apollo lunar lander was 4 meters across, or about 2 milliarcseconds at a distance of 385000 kilometers. The Hubble has a resolution of 50 milliarcseconds. Even the Hubble can't see the tracks and artifacts that the Apollo astronauts left on the Moon, let alone a backyard astronomer. Regarding a ...

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You can point a laser at the moon, but you won't be able to perceive any photons reflecting back. The beam spreads out due to diffraction. The rest of the illuminated side of the moon would far overwhelm your eyes, even at a slim crescent, to perceive any reflected photons from your laser. xkcd's What If? #13 shows what would happen if you got more people ...

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The first question anyone asks about a telescope is "what is the magnification?" It is almost always not the most important thing. Any telescope can magnify a million times, given a short enough eyepiece - the problem is, how good the image is. For observing planets, the main thing is resolving power - the ability of the telescope to discern tiny details. ...

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There are a few rules of thumb you will need: Maximum useful magnification $M_{max}\approx D\times 50$ where $D$ is the diameter of the objective is in inches, and magnification $M=l_{obj}/l_{eye}$, where $l_{obj}$ and $l_{eye}$ are the focal lengths of the objective and eye piece respectively.

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There are about 5 sporadic meteors visible per hour most nights, and since thousands of people were taking photographs of the moon that night, it is not impossible that someone captured a meteor in the same shot as the moon. A couple of things it was not It was not an unused satellite. When they re-enter you see a fireball as it breaks up, not a single ...

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