Imaging 7.4 magnitude star near limb of moon

[Arnold Ashcraft]

Folks:
I have uploaded two images to the files section. The first is from
a video taken at 9:47 pm EST last night of the star TYC-1401-1601-1
and shows the star, barely visible, about 6 minitues before being
occulted by the dark limb of the nearly full moon. As you can see,
the field of view is flooded with moonlight, in spite of the
excellent baffling of my Scupmann medial, and the moon is grossly
overexposed. This image was taken at an exposure of 1/4 second to
reveal the star, the moon would properly have taken only 1/50th of a
second or less exposure. The second image is a composite of clips
from a video taken at 9:51 and another at 9:53, just before
occultation of the star. The upper pair of images were taken
directly from the frames of the video with no processing other than
the application of the labels, but the lower pair were enhanced by
unsharp masking to reveal the star better.

This experiment shows that you can image a 7.4 mag star near the
limb of the moon, considerably brighter than the northern or southern
limb would be around 1st quarter, but only by overexposing the moon
itself.

File Name CAshcraft_20090209_0247346_ST64
Name of observer: Clif Ashcraft
Email address of observer: wa2...@optonline.net
Aperture of telescope: 184 mm
Focal length of telescope: 2578 mm
Type of camera used: The Imaging Source DMK31
Camera detector dimensions: 1024x768 pixels (uncropped)
Exposure information: 1/4 sec
Time and date of exposure: 2009-02-09 UT 0247
Location from which exposure was taken: Perrineville, NJ

File Name CAshcraft_20090209_mosaic
Name of observer: Clif Ashcraft
Email address of observer: wa2...@optonline.net
Aperture of telescope: 184 mm
Focal length of telescope: 2578 mm
Type of camera used: The Imaging Source DMK31
Camera detector dimensions: 1024x768 pixels (uncropped)
Exposure information: 1/5 sec
Time and date of exposure: 2009-02-09 UT 0251 and 0253
Location from which exposure was taken: Perrineville, NJ

Clif Ashcraft

[wa2...@optonline.net]

Folks:

        I just realized that I have neglected to state my routine use of a #25 red filter and NIR blocking filter in all my lunar imaging.  I do this to minimize image problems caused by atmospheric turbulence, and there is normally plenty of light from the moon.  There is little or no loss of resolution from the longer wavelength used for my images because seeing from my location is rarely (never?) good enough for my images to be diffraction limited in green light, let alone blue.  During the LCROSS impact observation, I may remove those filters to give me more sensitivity to help me image the plume.  At this point I am not sure whether this will be an advantage, particularly if there is any haze in the atmosphere, since blue light is more strongly scattered than red and any gain in sensitivity might be counteracted by greater influence of scattered moonlight.  If anyone has an opinion or facts to help me decide whether I should use or not use the filters during the impact event, please advise me.  I will make another try to image a 7th magnitude star near the bright lunar limb tonight without the filters to see if it changes my results one way or another.

                            Clif

> --~--~---------~--~----~------------~-------~--~----~
> You received this message because you are subscribed to the
> Google Groups "LCROSS_Observation" group.
> To post to this group, send email to
> lcross_ob...@googlegroups.comTo unsubscribe from this
> group, send email to lcross_observat...@googlegroups.com
> For more options, visit this group at
> http://groups.google.com/group/lcross_observation?hl=en-~--------
> --~----~----~----~------~----~------~--~---
>
>

[Derek C Breit]

If anyone has an opinion or facts to help me decide whether I should use or not use the filters during the impact event, please advise me.

 

 

I can only respond from a video point of view..

 

It depends on the spectral response of the detector..

 

Our video cameras, of a SuperCircuits PC164 type or similar, are very responsive in the IR and I know of no one that uses an IR filter for lunar occultations. Doesn't mean they don't, just means I don't know about.. Some use color filters depending on the target and the goal.. Red is the most common mentioned. I do not own either an NIR or any color filters and have no personal experience on them..

 

The Simple answer is to try it and see what it does to your SNR to stars near the lunar limb..

 

A variable polarizer, especially one you can adjust on the fly as conditions change, would be handy..

 

But come crunch time, I will be videotaping without filters so I can get all the signal I can..

 

And while a scope may be well baffled, what about the camera??

 

See the following link, and note the difference to the silver ring with and without black flocking.. That makes a huge difference to eliminate reflections, in my case off of the backside of the focal reducer (or barlow)..

 

http://www.poyntsource.com/BREIT_IDEAS/images1.htm

 

Derek

 PS.. KURT.. Thanks for the "Illuminated Fractions".. !!!

I can wait for early March.