The Night Sky Live for Scientists

The first question many people ask when presented with the Night Sky Live Project is how these seemingly mundane images can be used for real scientific research.

There are in fact many different ways, most of them stemming from the advantage of watching the entire sky at once. What each CONCAM lacks in depth or detail as compared to a large astronomical telescope, it makes up for in seeing the entire sky at once, not missing a thing. Combine this with long-term, low or no-cost observation capability, and multiple locations around the world, and you have a unique platform for spotting surprise phenomena that you couldn't catch with a telescope. Combined with reliable photometry data, this presents an powerful platform for either target spotting with larger telescopes or research using data straight from the CONCAMs themselves.

Types of Data Collected

WOLF was developed specifically for the Night Sky Live by Lior Shamir, to analyze CONCAM images and output several useful sets of data, which are detailed below.

• FITS
  The raw exposures from the CCDs inside the CONCAMs are saved as the scientific image format, FITS. Unlike normal graphics formats, a FITS file stores each pixel as a count, from 0 to 65536 (2^16). This count reflects the number of hits on each individual pixel of the CCD itself. Thus, photometry calculations can be made either by using a FITS-compatible viewer (such as fv (link)) or by using WOLF.
• Background
  WOLF can generate an image of the background of the sky with stars removed. This is very useful for the observatories that have a CONCAM as it gives them a good idea of how much light pollution is in the sky around them. Example.
• Opacity Maps
  WOLF is able to automatically detect the opacity of the sky, which gives us a very good idea of the atmospheric conditions above the CONCAM, which may not be readily apparent to the naked eye.
• Photometry
  The photometry data collected by WOLF is listed in tables on HTML files. There are two sorts of photometry files: one for each individual image, and a second set for each individual star over the course of a night (although only the brightest stars are currently automatically collected).
• Annotated Images
  WOLF generates JPEG files automatically labeled with star names, constellation names, planets, and it can even detect transients. In addition, any object can be manually added to the catalog, such as comets or galaxies, for quick identification. Any object added to the catalog will also have photometry data taken for it. Unannotated images are also available.

Opacity Maps

Opacity maps can be used to determine whether the data is being affected by atmospheric conditions. For example, while a certain night may look clear, the photometry of a star may exhibit strange jumps up and down. However, it can be easily explained if the opacity maps for the night show atmospheric disturbances, such as clouds or turbulence.

The darker blue on the frame with the opacity map indicates where WOLF has detected atmospheric opacity. You can see some of the areas in the unmarked frame as obvious clouds, but other areas aren't quite as obvious.

Using the Photometry Data

Each individual frame taken from the CONCAMs has it's own page filled with photometry. We'll use a page from the Canary Islands as an example.

The data at the top includes the date, universal time, julian date (JD), exposure length (all usable images should be 180 seconds), and the filename of the FITS file.

Each star is kept track of with an HD number as written in the catalog, along with the name. At the top of this page is HD8890, Alpha Ursa Minoris, also known as Polaris.

• C5 is the average of the 5 brightest pixels around the center of the star.
• B is the brightness of the background around the star, and the average of the 1600 pixels around the star (20 pixels in each direction, 40x40 grid)
• x & y are the coordinates of the center pixel of the star (also known as C1) on the FITS file.
• az & alt are the azimuth and altitude.
• Type is the spectral type of the star. Note that the CCDs in the CONCAMs are more sensitive to the red portion of the spectrum.
• V-mag is the visual magnitude of the star.
• C-mag is the magnitude as estimated by WOLF.
C5c-Bc checks the frame against an accepted value of the star, to help identify usable frames.

Many of the brighter stars also have their own photometry pages, one for each night. The pages are named, in the example of Polaris, HD8890.html, as with the link on the above page to http://nightskylive.net/ci/ci040519/HD8890.html.

• C1-B is the brightest pixel of the star minus the background
• C5-B through C25-B are the average of the x brightest pixels of the star minus the background

Page written by Dan Cordell, Vic Muzzin, and Matt Merlo