Saturday, January 16, 2010

Dora Medium Goody Bags

How do I choose a suitable device for CCD? (I) Image scaling eruption

When moving into the world of photometry, the observer can come up with a novel preconceived ideas or no idea at all of the precision that will take your measurements. The CCD camera sounds like the Annunaki p the photometric measurement but this claim is among the inaccurate and misleading.
CCD technology really do not think it will disappoint anyone, but you can not independently assess the system opt ico with which you work.


There is a very important factor in the shooting, which is the scale, ie, the angular size on the sky covered by each pixel of the detector. This is given by the ratio between the size of the image element and the focal length, from among the following:


where P is the scale (in arcseconds per pixel; "/ pixel or arcsec / pixel ) μ pixel size in microns F the focal length of telescope or objective.

There
on the web utilities to calculate the scale given a telescope and a particular camera.




doing we must optimize scale images properly selecting a camera based on the optical available, or choose a CCD and a telescope that fit, so that covers the maximum pixel resolvable angular distance on the place of observation, with the equipment available. No mention of the theoretical resolution of the telescope ( Dawes limit), but the resolution allowed by the stability of the air at the observatory, which is often referred seeing.


The stars are scattered, in theory, as can be observed from Earth. But the wave propagation of light, we observe a large spot produced by the diffraction of light. In turn, the atmosphere alter light rays that reach us by enlarging false stellar disk, so that the size the figure is equivalent to the resolution achieved in our sky conditions.


The typical seeing usually two arc second for most locations, and this proves to be an overly optimistic estimate. In the nights are not stable under the 4 "of FWHM (full width at half intensity is like measuring the apparent size of a star on picture and talk about this concept in another post), and if I can stay in 5 "I think I'm singing in the teeth. My telescope is of reasonable quality, but I'm in a very inappropriate remark wing pair that, for example, warming day of the facade makes current flow of unwanted air that degrades the image.


Even with everything we have to accept a conventional value scale to serve as a standard image, and 2 "/ pixel is a valid reference, or a range between 1 and 2" / pixel. From this threshold, with a smaller pixel or a longer focal length would be less than 1 "/ pixel, which is called upsampling (oversampling). This setting is used in applications of high precision astrometry of the stars double for planetary images, or instruments, generally large professional telescopes, which give conditions exceptional seeing (for good quality local sky and the use of adaptive optics). Under no circumstances should be avoided since each star's light is spread over by the CCD pixels.


If the scale is greater than 2 "/ pixel, if the focal length decreases (or the pixel is larger) the conditions would subsampling (subsampling), which would be critical if P> 5" / pixel. Upsampling (oversampling) is not to exploit the maximum resolution that offers the observation, and should be avoided because it allows the light from stars can be collected with maximum efficiency, which photometric and astrometric measurements can not achieve optimal quality.

Friday, January 15, 2010

Driving Simulation Game

UV Persei

On January 3, 2010 Gary Poyner, an amateur astronomer, reported to the VSNET mailing list Japanese UV Persei the outbreak of a cataclysmic variable star popular enough variability. Part of its charm is its location, close to the beautiful double cluster in Perseus.

However UV Per is expected. And it can happen between 300 and 400 days at rest, at its minimum brightness, about 17-18 in V-band magnitude (which is practically impossible to observe visually through an eyepiece, just register on CCD images). Enters suddenly burst and the magnitude is almost 11, ie, it becomes about 250 times brighter (¡!).

At the time I took the image illustrating this post, last night, the star is already declining in brightness, with a 13.33 magnitude in V filter photometry gave me.

The observation of variable stars, as reader you can imagine, has a good deal of patient waiting.

Friday, January 8, 2010

Regal Kitchen Pro Bread Maker

And this is a book? (II) Variable Stars

It's really difficult to recommend literature on variable stars by the limited number of published works covering the subject of a monograph. The student has traditionally had to fend of the references in manuals or general astronomy, tangentially, in trials of stellar evolution.

To be honest, the topic of stellar variability has been being a minority even within the field of astronomy in general and astronomy publications. Thus, if we look for books in English, published by a commercial just once. The only title is Variable Star (Ed. Team Sirius) of Jaime Rubén García to , astronomer with the subject, scientific director of the Copernicus Institute in Argentina (and currently president of the AAVSO )

Variable Star
a journey through the different types of variability, descriptively, to provide an overview. Is a right book to enter in the discipline, but very fair for an introduction to the observation of variable stars.

The Watcher of the Cosmos, Manual Observing Ripero of José Osorio , published by Sirius Computer too, is an introductory manual to the general astronomical observation, but has an extensive chapter on visual observation of variables.

The author knows of what he writes, with an experience of over 30 years of observation variabilística, contributing their observations to the AAVSO, VSNET AFOEV and other groups. Included are letters AAVSO observation reproduced with permission for the reader to make his first steps in the estimation of brightness.

As a reference manual, practical skills for observation, we have the excellent Manual visual observation of variable stars in the AAVSO . Is excellently prepared by expert observers and is free if downloaded in pdf format from the web of the organization. To be translated into several languages, including English, many non-English speaking fans can start in this world.



But, alas, for a detailed study once again, is to dip into the English literature. David H. Levy wrote the great manual Observing Variable Stars: A guide for the beginner , which taught from scratch how to learn to watch the sky by recognizing the constellations, to be observed by telescopes and binoculars estimate the brightness of variable stars. It explains the different types of variability with concrete examples of stars, very entertaining and full of anecdotes. The book is reissued with the title of David Levy's Guide to Variable Stars (Cambridge University Press).



Understanding Variable Stars in John Percy, published by Cambridge University Press. This is almost the definitive work for those who want to know all kinds of variable stars and the mechanisms of their variability. From an introduction to the structure and stellar evolution, through the fundamentals of photometry to be examining in detail characteristics of each type of variable and established models to explain them.

of the creditworthiness of the author, a professor of astronomy and astrophysics at the University of Toronto, Canada, and one of the largest global espcial variable stars (particularly of the pulse variables) speak eloquently of the test pages .

If the reader noticed it, most of the literature listed in this post and the previous one is in English. For anyone who wants to enter and advance in astronomy, and specifically in the study of variable stars, knowing the language, at least read it, is almost as important comodisponer a telescope and a CCD camera, so to learn English! .