Comet Machholz (C2004 Q2)- fourth and last night

Science at Parramatta High
Comet Machholz - (C2004 Q2)
— January 12 2005 —
...and a question of colour (see below)

Machholz says farewell to Parramatta High. This was taken at 9:30pm, just before he sunk into the trees.
This time of the year, that's also about the earliest we can take astro images (daylight savings, and all that).
Below is a detail shot of the above image.

Now - as to the colour of the gas cloud around the comet.

Earlier images ( Jan 6, Jan 7 ) show the gas cloud as distinctly green. The film images ( Jan 10 and above ) render the gas cloud as predominantly blue.

Which is "correct"?

The green image was captured with a Nikon Coolpix 5700, set at 8 secs with noise cancelling. (This feature exposes two dark frames -one before and after the image- which are automatically subtracted from the final image.) It works very well. I tried a few shots without noise cancelling, and they were rife in bright red and green "hot" pixels.

The colour of the comet (green) was identical in both cases (with or without noise cancelling).

The bluish image was taken on 35mm colour reversal film (Kodacolor 400), scanned on an HP S20 film scanner and processed with no alteration to the color balance.

A daylight reference photo is available here, here for comparison purposes. It is on the same roll of film, used the same lens and was scanned and processed identically to the comet images. The accuracy of the colours seems to suggest that any color "mask" is not due to the film (per se), the scanning or the post-production.

Film loses sensitivity and changes colour balance as exposure time increases. This is called "reciprocity failure" and is the likely cause of the blue caste over the film images.

Back to Jan 6 images.
Back to Jan 7 images.
Back to Jan 10 images.

Back to astro images index.

Break out
of this frame.