## Differential Equations -A

Posted March 25, 2010 By grigoris

Solutions of a second order differential linear and homogeneous equation with constant coefficients: a y” + b y’ + c y = 0 (a ≠ 0) Solve the characteristic equation: a r2 + b r + c = 0 with general solutions r1,2=[(-b±√b2-4ac )/2a]. 1> if Δ=b2-4ac > 0 then the solutions r1=r1 are real […]

## Manipulating postscript/pdf files

Posted March 24, 2010 By grigoris

Postscript files (.ps) are usual and in many cases some manipulation is needed. [for more see also here] Convert from a ps to pdf file: \$ ps2pdf input_file.ps output_file.ps Merge 2 or more files: \$ psmerge -ooutput_file.ps input_file_1.ps input_file_2.ps [more_files] note: that -o and output_file’s name are not separated by any space Put more pages […]

## Sexagesimal and radian to degree conversion

Posted March 23, 2010 By grigoris

A. If you want to convert sexagesimal numbers (RA=hh:mm:ss.s Dec=±dd:mm:ss) to degrees then use these relations: RA>deg: 15 x (hh + mm/60 + ss.s/3600) Dec>deg: ±dd ± (mm/60 + ss/3600) These relations are pretty easy to remember since > 1 hour the sky rotates 15 degrees (360degrees in 24 hours) > 1 minute = 60 […]

## WhereIsM13 and .jar files

Posted March 18, 2010 By grigoris

WhereIsM13 is a great 3d visualization application of deep sky objects! You can see where these objects lie in our Galaxy along with their physical properties. There are different download options according to the operating system. For linux users download the .zip version which includes a .jar file that can be run by double clicking […]

## William Parsons – first direct observation of spirals

Posted March 18, 2010 By grigoris

William Parsons, was the first to notice spirals in a galaxy. His first scetch was the M51 (Whirlpool Galaxy) in 1845. More on William Parsons: > Wikipedia > A list of photos & discoveries > Drawings

## DSLR processing and photometry for epsilon Aurigae with IRIS

Posted March 17, 2010 By grigoris

Prepared for the CitizenSky.org ‘s DSLR tutorials (with the help of bikeman and Roger_Pieri). CitizenSky.org is dedicated to the eclipsing binary epsilon Aurigae, but the procedure is more general and can be applied to any star. ~ ~ ~ For easiest use download the last version of IRIS 5.58 (especially for any Linux user because […]

## Interesting Hertzsprung–Russell diagrams

Posted March 8, 2010 By grigoris

Two very interesting images about the H-R diagram! The Hertzsprung–Russell diagram is a scatter graph of stars showing the relationship between the stars’ absolute magnitudes or luminosity versus their spectral types or classifications and effective temperatures. This diagram below is a plot of 22000 stars from the Hipparcos Catalogue together with 1000 low-luminosity stars (red […]

## Software for variable stars

Posted March 6, 2010 By grigoris

A not exhaustive list of software suitable for variable stars (e.g. reduction of images, photometry, period search, etc.). 1. IRIS 2. Period04 3. IRAF 4. AIP4WIN 5. Mira 6. MPO Canopus 7. MaxIm DL 8. Peranso 9. C-MuniPack Project 10. VStar on CitizenSky.org, AAVSO, or Sourceforge 11. AVE [added on 10/3/2011] 12. AstroImageJ [added on […]