David's Astronomy Pages Notes - Session 108 (2006-01-01) Notes (S107)   Notes (Main)   Home Page   Notes (S109)

Goto Images from 2006-01-01

Sky Conditions

Sky Condition Summary (Session S108)

Notice  1)

• Airmass of image. Purple Line
  1 is zenith, with higher number indicating positions progressively towards the horizon
  

• Sky Brightness.  Red circles/line.  
  Sky Magnitude in mag per sq. arc sec. Higher numbers (towards top of chart) indicate darkest skies.
  

• Elongation.  Red circles/line.  
  Elongation (long axis length/short axis length). 1 = circular star image.
  

• Mag Zero Point. Green circles/line.   
  For each Clear Filter image this is the average difference between the catalog magnitude of stars and their instrumental raw magnitude normalized to a 1 sec exposure.  Only sharp star-like objects are used in this calculation.  Larger numbers (towards top of chart) indicate more transparent skies .   Lower numbers indicate either a less transparent sky or the formation of condensation/dew on the front lens of the telescope.
  

• ZP. Small green circles
  These are magnitude zero points for individual stars in Clear Filter images. The range is due to a number of factors including catalog magnitude error, star colour, impact of star brightness on S/N
  

• FWHM (clear). Blue diamonds
  There are the Full-Width Half Maximum measurements of individual stars in Clear Filter images.  Only sharpest star-like objects above a S/N threshold are shown. Lower number (towards top of chart) indicate best seeing (most stable atmosphere) and best focusing.  Note that seeing & focusing may drift over an observing session.  
  

• FWHM (RGB). Orange diamonds
  There are the Full-Width Half Maximum measurements of individual stars in Colour Filtered (RGB) images.  Only sharpest star-like objects above a S/N threshold are shown. Lower number (towards top of chart)
  

• FWHM (RGB). Small white circles
  These are objects that fail to meet sharpness & S/N thresholds.  They might include galaxies or low S/N stars 
  

Sky Conditions Chart (S108)

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Impact of Light Dew/Condensation on Faint Galaxy

The impact of just a light dew / condensation on ability to image a faint galaxy is shown by the following frames of irregular galaxy NGC 1156.

NGC 1156  -  Light dew on front lens of scope		NGC 1156  -  Front lens cleared of dew
CCD Image  120s, clear filter 2006-01-02 00:42h UT (#108109)		CCD Image  120s, clear filter 2006-01-02 00:49h UT (#108112)

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Use of Log brightness scaling / False Colour by highlighting detail in faint galaxies

Logarithmic scaling and false colour was used to highlight detail in images of several galaxies recorded during the S00108 session. The following example shows the spiral galaxy M109.

M109  -  Normal Image		M109 - Log brightness scaling & False Colour
CCD Image  6 x 2 min (average combine), clear filter 2006-01-02 01:12h UT (#108113-18)		CCD image as left  with log brightness scaling & false colour (inverse spectrum)

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