| The Virtual Observatory for Amateur
Updated 1st January 2021
Exercises using the Virtual Observatory
Following the lecture I have delivered to a number of societies about the The Virtual Observatory for Amateur Astronomers. The questions asked and subsequent discussions indicated that there is so much in the Virtual Observatory that people don't know where to start. As a result I have written a number of exercises that are designed to 'break the ice' and to aid you getting familiar with the various facilities of the virtual observatory. The exercises start with a very gentle introduction and then build on this. Most exercises assume familiarity with the material covered in the previous exercises so it is best to attempt them in order.
The following exercises are designed to introduce you to some of the facilities available to Amateur Astronomers in the Virtual Observatory. The first exercises are designed to introduce you to the AVO. The initial exercises will concentrate on one of the graphical front ends to the VO called Aladin as this has a powerful graphical interface that allows you to explore large sections of the VO as well as using the facilities for your own projects. Where possible hyperlinks to the various programmes and websites have been included as clickable links.
For some exercises you will require additional images or software. These will be shown at the start of each exercise.
Earlier versions of Aladin were limited in the area of the Sky which they would show to the size of the images in held in the server - often a fraction of a degree. This also created problems if the area you were interested on was in the border of several images. Attempting to download catalogues for large areas ran into problems due to the large amount of data. In version Aladin Version 7 a new mode was introduced - the progressive mode that allows you to download large areas of the sky and also makes this the default option if you just enter an object in the 'Location' box. Indeed if you do not enter an object you will get an image of the whole sky. A number of quick load buttons have been provided for the 'progressive' mode just above the image area. There are three images All Sky Optical (coloured), All Sky Infrared & Digital Sky Survey (monochrome). In addition buttons provide access to the Simbad, NED, PPMX & 2 Mass catalogues in progressive mode. Further images and catalogues are available under the new 'File' - 'All Sky' option.
The original mode is still available by loading the images and catalogues using the functions on the file menu. In this mode a lot more images and catalogues are available but the images are limited by the size of individual images held on the server - there is no automatic tiling mode. .Also a lot of images taken by surveys only cover part of the sky so donít be surprised if your favourite images or survey are not available for the area you are looking at.
There have been a number of other changes that have effected the exercises below - I have put some notes against these until I can re-write them
In addition to the exercise number the list below shows the programme that you will learn about and brief summary of what the exercise is designed to teach you
To run Aladin you need a computer that has Java installed (most have). There are no special hardware requirements though a large monitor running at high resolution is helpful to see some of the fine detail. The exercises should run under Windows, Mac and Linux Operating Systems though the methods of installing Aladin are different. You will also need a high speed Internet connection as some of the images and catalogues are quite large. You will also need a reasonable amount of spare space on your hard disc as the uncompressed FITS format images tend to be quite large.
VO Software Changes:
The exercises were designed around version 6 of the software. Due to the rate of change of the VO the software may have been upgraded and additional functionality added by the time you try these exercises. Aladin V8 was issued in February 2014. The exercises should work under this version but there may be some differences in the user interface.
Exercises 1 to 5 plus 10 & 12 are available. There is a link to a file that covers Exercise 7 as well. Exercise 12 is numerically out of order but is in the logical place - it's not so much an exercise as some notes to help you.
The other exercises will be added as I write them and verify them. The exercises in magenta Italics have yet to be written and may be changed.
Note: 8/5/2011 - Exercise 10 has been added - the exercise to plot all the Globular Clusters is now an additional activity at the end of exercise 10 so exercise 9 which was out of order is no longer required.
Update 22/6/2015 Virtual Observatory Examples on EuroVO:
A large number of examples on how to use the Virtual Observatory can be found on the EuroVO for Education (revised link) page . I have removed the links as the list of examples is extensive and growing. Some of these are more general astronomy exercises rather than dedicated to using the VO and may be useful for astronomy education.
Update 29/1/2016 Virtual IObservatory examples for 'scientists'
The list of examples on the EuroVO page for scientists and students has been expanded in December 2015 with several new examples that are worth trying to understand the facilities available in the VO as well as learning a bit of astronomy.
Practice Using Aladin to download & analyse images & data
The Aladin Website has a number of exercises available to help you develop your skills using Aladin and to show some of the features of the programme. The exercises are colour coded to show you the easier and more difficult ones. Some of the instructions are a bit terse but try them and see how you get on. In due course I hope to expand this section to give you some tips on the exercises and some information on other things to try.
One thing to note with Aladin is that you should be very careful with the delete (X) function. There is no 'are you sure ?' warnings and it is very easy to accidentally delete several image & data planes - I know I have done it !
The exercises require at least Aladin V7 so if you have an older version delete this before you start. In addition you may need to run the Standalone version (see exercise 12) to allow you to download your own image in exercise 3.
When you have tried an exercise experiment by changing some of the parameters or varying the conditions in the filters. Only by trying things yourself will you learn what it is all about and become an Aladin Wizard !
22/6/2015 Use of TopCat for exploration of data sets and producing target lists
TopCat ( Tool for Operations on Catalogues) began as a Starlink tool several years ago but has been expanded and developed to meet the requirements of the VO. If you have not used it before but are aware of spreadsheets the loaded catalogue can be thought of as a large table in a spreadsheet with column headings and lots of rows. The significant difference is that you cannot carry out mathematical operations on individual rows as you can on a spreadsheet. Instead you create a new column which is some mathematical combination of other columns. If you want to use the data from individual rows you do this by creating a sub-set that labels just those rows you have selected. There are some neat tools as well for instance if you plot some data using the extensive plotting facilities and you want to select a sub-set of interesting data - for instance think of the white dwarfs in the HR diagram, you just draw round the relevant data points and create a sub-set from them.
Rather than write my own set of exercises for TopCat have a number of examples have been created by the author of TopCat here. These were created for professional astronomers as part of a workshop on Brown Dwarf stars. One thing to note that in the exercise to locate the co-moving group of stars in the Pleiades as shown in the image of the TopCat window on the right., there is an optional exercise to send the selected co-moving group or indeed the stars that are not a member of this group using SAMP. Two ideas to experiment with are to send it to Cartes du Ciel where you can see the sub-set against the stars of the Pleiades (it helps if you have a calibrated image of the Pleiades in CdC first) or else send it to Aladin where you can load a background image of M45.
Another idea is to plot a 'Colour -Magnitude' diagram for both sub-sets to see what that reveals about the two populations of stars.
This exercise covers the principals of my VO exercise 13 and part of 14 as listed above.
One other interesting tool is buried in the example above. In Exercise 1 step 4 as an alternative to downloading the Pleiades Tycho2 catalogue from VizeR you can load the data into TopCat using the Click Box via SAMP. This uses another piece of VO technology that allows web pages to be broadcast to a SAMP hub and then on to other applications. More details are on the WebSAMPConnector page.
© John Murrell 2021
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