C-WAYS Resolution Worksheet

Introduction

The spatial resolution of various instruments and missions is and will be a very important thing for us to consider in the course of assessing the literature studies of our regions, as well as doing our project with WISE and Spitzer data.

For a general introduction, please start with the main text already on the wiki for Resolution. Please look at the examples lower on that page, but you don't need to actually do the one that suggests that you go download data, etc. The skills you might have gained from that will be stuff that we will either do as part of this worksheet, or as part of our Summer visit.

We will be using Goddard's Skyview for this worksheet.

Each of you should be assigned as a primary person for a BRC target (since there are 5 core educators, and 3 BRCs, we have room for one more 'primary' -- mark legassie??). If you finish doing this for 'your' target, or want to continue exploration of one of the others, or another target entirely, please go ahead and do so!

Skyview basics and other things to note

We will be using Goddard's Skyview. There is documentation linked from that front page. We will use the full Query form, not the Non-Astronomer's page.

If, in the future, you need to find this, you will probably need to google "Goddard Skyview" as there is at least one other software package called Skyview (including one at IPAC that is mentioned more than once here in this wiki) that does something else entirely.

I WILL MAKE A YOUTUBE SCREENCAPTURE MOVIE TO GO HERE

Skyview pulls together some huge number of surveys in one place and makes them accessible to you in an easy, fast interface. It will resample and regrid and remosaic all sorts of surveys for you, from gamma rays to the radio. I don't know exactly if it conserves flux (e.g., if one can still do photometry off of the mosaics it provides); I would err on the side of caution and NOT use this for anything other than morphology, e.g., do science by eye with the mosaics, and you can use them for distance measurements, but don't do photometry on these mosaics.

Skyview will always spawn the same second window for the results. The first time you call it, it will spawn a second browser tab or window (depending on your local configuration), and then, if you don't close that second tab or window explicitly, the next search results will go into that same window, even if it's hidden below where you are currently working.

Skyview will give you a JPG right away, and allow you to download both the JPG and the FITS file. (Slightly more information on FITS format is elsewhere on the wiki.) JPGs (and for that matter GIFs or PNGs) are "lossy compressed" files, which means that it actually LOSES INFORMATION, certainly compared to the FITS file. JPGs are just fine for images you take of your kids with digital cameras - you rarely ever see evidence of the loss of information. (As an aside - you might see evidence of it if you take a picture of something with sharp contrast, or a sharp edge somewhere in the image. If you look at the jpeg up close, you will see 'ringing' of the sharp edge, which looks kind of like blurring. The wiki page on lossy compression above has an example of loss of information with pngs.)

So, what this means is: any time you are doing science, whether that is using your eye to see small details in the image, or measuring distances, or doing photometry, you always want to be using the FITS file, never a JPG, PNG, or GIF.

Therefore, you will need software capable of reading FITS files. There is some information on using a variety of platforms [| here], but you might as well start to get comfortable with using ds9, since that's what we will be using later on in the project. There are at least 2 tutorials on using ds9 developed by NITARP students on the wiki for doing some specific things - search on ds9.