Archive for 2010

The Geminids are one of the best meteor showers of the year with numerous (ZHR~120) and bright (r~2) meteors! The parent body is an asteroid named 3200 Phaethon, which is believed to be a candidate for an extinct cometary nucleus, a mystery by itself. Moreover, during the last perihelion passage of the asteroid its magnitude increased unexpectedly (almost doubled), which is thought to be connected to some ejected dust originated from break-down of surface rocks. But this dust can account only for the 0.01% of the total material which is needed to supply the stream in order to see this activity each year this show.

How this object has manage to give out so much material? Geminids are not ready yet to reveal their mysteries…

The source and paper ( by journal or author) / Jewitt D. & Li J., Activity in Geminid parent (3200) Phaethon, AJ, 140, 1519, 2010.

Changing file ownership

Posted November 29, 2010 By grigoris

These are two commands to help us change the ownership of files, but we must be in the root or su mode first.

> chown <username> <file/folder> : used to change the owner of a file or folder

> chgrp <group> <file/folder> : used to change the group of a file or folder

> chown <username>.<group> <file/folder> : used to change the owner and the group in one step

> chown -R <username>.<group> <folder> : used to change the owner and the group of ALL files and directories under the parent <folder> (a very useful command !!)

(thanks to this post!)

Extracting rpm and deb packages

Posted November 4, 2010 By grigoris

[ Information from G-Loaded journal – many thanks! ]

The packages rpm and deb are used mainly by the package managers in order to easilly and successfully install any additional stuff. At the same time rpm and deb packages are also archives (cpio and ar archives respectively) that can be axtracted.

One way is of course to right click on the package and select extract as any nomal archived file (double-click will start the package manager and the installation process, something that we don’t want now!) .

A second way is through the command line:

For rpm (Fedora, RedHat, etc):
rpm2cpio mypackage.rpm | cpio -vid
and for deb (Ubuntu, Debian, etc), which contains three files (debian-binary, control.tar.gz, data.tar.gz – in which we are actually interested in!) :
ar vx mypackage.deb
tar -xzvf data.tar.gz

The -v option is optional, so if used then you get verbose output.

Then you can use the output (found on usr/ folder) as you want – my initial motivation was to to find a library needed for a 32bit program installed on a 64bit machine!.

Installing WCSTools

Posted October 4, 2010 By grigoris

WCSTools is a package of programs and a library of utility subroutines for setting and using the world coordinate systems (WCS) in the headers of the most common astronomical image formats, FITS and IRAF .imh, to relate image pixels to sky coordinates. This software is all written in very portable C, so it should compile and run on any computer with a C compiler. ”

Apart from the main purpose that WCSTools has, there are some useful utilities for FITS header (like edhead, gethead, imhead). That’s why I decided to install it after all…(installation process based on this ubuntu thread)

First download the latest verion (currently 3.8.1) from the anonymous FTP:

From the directory that tarball was downloaded, go to a tcsh (or any c-shell), if you are not, and untar:
tar -xvf wcstools-3.8.1.tar.gz

Go to the created directory and set the environment for the c compiler:
cd wcstools-3.8.1
setenv CC gcc
setenv CFLAGS "-O2 -pipe -fomit-frame-pointer"


Create and move the binaries created to the desired path
mkdir -p /desiredpath/wcstools/
mv bin /desiredpath/wcstools

Edit you .tcshrc (or .cshrc) file (back to the home directory, if different) and add the path of the binaries created:

# wcstools path
set path=($path /home/user/desiredpath/wcstools/bin)

Then source the .tcshrc file:
source .tcshrc
or restart the terminal to activate the new commands!

~ ~ ~

UPDATE (28/01/2015): For Debian the installation is even simpler [1] … just:
sudo apt-get install wcstools

[1]: “How to install wcstools package in Debian Wheezy”, accessed on 28/01/2015,

Exif meta editing

Posted September 30, 2010 By grigoris

If you want to mess with the exif headers of your pictures there are a couple (not only of course!) of useful tools:

>> jhead (for jpeg images)

>> exiftool (supporting many different file formats).

Using wine

Posted September 27, 2010 By grigoris

The command to start a program through wine from terminal or through a shortcut is:

env WINEPREFIX="/home/user/.wine" wine "C:/somefolder/name.exe"

The wine is a open source simulator to run windows software under linux (and others).

Welcome (again) …

Posted September 1, 2010 By grigoris

to a new and more serious attempt* to build a site about my personal work on Astronomy, a long-time hobby that became a demanding job since June 2010!

Mainly, the blog will work as a personal notebook where you may (or may not!) find something useful. You will be able to find from small tips to tutorials, from software hints to hardware solutions, from theories to observations, from small articles to papers and anything that has to do with Astronomy (ok… perhaps some more general stuff also!).

The other pages (will) include information about my research projects (PhD thesis and more) along with extra information about me…

I hope you enjoy and find something useful. If not, what the heck … nobody is perfect!

*I have been using blogger since January 2010 (I even tried the free wordpress), but the limitations of the free services “forced” me to go for personal solution, so as to be totally independent and free to build and maintain a robust site from the beginning the way I prefer.

Hypervelocity star – HE 0437-5439

Posted August 3, 2010 By grigoris

An interesting story on hypervelocity stars. Around 16 know since 2005, one of them being the HE 0437-5439 which travells at 2.5 million kilometers / hour. The puzzle about this is that it is too young to have travelled so far from the Wilky Way (200 000 light-years over the disk plane).

The story (?):
“A hundred million years ago, a triple-star system was traveling through the bustling center of our Milky Way galaxy when it made a life-changing misstep. The trio wandered too close to the galaxy’s giant black hole, which captured one of the stars and hurled the other two out of the Milky Way. Adding to the stellar game of musical chairs, the two outbound stars merged to form a super-hot, blue star.”

Hubble NewsCenter release & the ApJ Lett paper / Warren R. B. et al, A galactic origin for HE 0437–5439, the hypervelocity star near the Large Magellanic Cloud, ApJ, 719, L23, 2010.

The 4th Panhellenic Meeting of Amateur Astronomers took place in a magnificent area, at the mountain refugee of the Mountaineering Club of Sparta at Mt. Parnonas. The place is located at ~1400m with a huge field working as the best place to park cars and set up all the necessary equipment. Moreover, the area around is full of trees and a fantastic place for camping. More or less 415 people gathered, more than 100 telescopes, 3 nigths of clear unobstructed dark skies, 6 observational workshops (participating in 2 of them: variable star observations and optical observation methodology of meteors) and some talks, and other activities (great for MTB!!) were enough to satisfy even the most demanding person. The organizing commitee did a great jod and managed to fulfill all the needs (both astrononomical and personal).

More available only in greek but no need of language to see photos.

First observations from Skinakas

Posted July 26, 2010 By grigoris

From 30/6 up to 5/7 I found myself observing from Skinakas Observatory for the first time (doing photometry tests on a number of exoplanet candidates) ! That was really a great experience and I enjoyed much both the procedure of observations and the stay there at the mountaintop. Only the weather could have been a little better the last nights as the humidity was getting very high, halting the observations. Anyway, we cannot predict yet the weather that good!

skinakas2010aSkinakas‘ dome on the left and Capella‘s dome on the right, during the sunset.

skinakas2010bSharing the mountaintop.