Recently, on May 2nd of 2006, astronomers using a 10 inch Schmidt Cassegrain telescope imaged the impact of a small meteorite on the dark side of the lunar terminator (http://science.nasa.gov/headlines/y2006/13jun_lunarsporadic.htm). The impact flash was 7th magnitude and lasted only a fraction of a second.
My goal is to attempt to obtain spectra of such an impact flash using my 9.25" F10 Schmidt Cassegrain telescope with a simple low resolution spectral grating (100 to 300 lines/mm) such as is available from Rainbow Optics in the US or the Hawksley company in the UK. This is not a simple task because the spectra of a 7th magnitude flash will be much fainter due to the spreading out of light and because the flash is or such a short duration. To maximize my chances of obtaining spectra in an event of this type, I believe that it would be advantageous to use a very light sensitive videocam. My initial choice was the Watec Wat-120N monochrome camera although I have since acquired a Su320MX short wave infrared camera which could be useful although it does produce many more hot pixels than the Watec camera. Cosmic ray flashes only are present in a single 1/60 sec frame and false flashes due to camera noise in only one or two 1/60 sec frames. The duration of a real impact flash is likely much longer in the near infrared than if imaged at a visible wavelength. One experienced imager believes that a lunar impact flash that would last only 2 frames in visible light could last as long as 45 frames when imaged in the infrared between 850 nm and 1100 nm. So, this is an interesting area for further future study using a pure NIR camera like the Su320MX or a visible camera with some extra NIR coverage like the Hitachi KP-M2RN or KP-F2A.
Camera analog output is brought into a Canopus ADVC110 framegrabber to convert selected frames from a long monitoring session into digital format. I plan to monitor the dark side of the lunar terminator before 1st quarter and after 3rd quarter and see what happens... If spectra of a flash can be obtained then they will argue strongly that the flash was in fact caused by a meteorite impact since a cosmic ray or "hot pixel" would not produce spectra. Imaging will be coordinated with major and minor meteor showers to maximize the possibility of recording an impact event. Schedules of meteor shower activity are available from the American Meteor Society.
The basic setup of the Watec camera, laptop, Canopus framegrabber, and monitor are shown below:
A video cassette recorder can be added to the setup to make long duration recordings of the dark side of the lunar terminator. These recordings can be played back later and the clips of any observed impacts can be digitized with the framegrabber by advancing to that point on the videotape and plaing the tape while the framegrabber is on and exporting to Windows Movie Maker on a laptop. Videotape may produce more artifacts than simply recording an avi file to hard disk which is likely the better option. The Watec 120N camera would usually be used at prime focus. It is a big advantage to have a KIWI OSD time encoder superimpose the exact time onto the video signal (see link below). More information on equipment setup and on the latest software tool in detecting impact flashes (the lunarscan program, a free download) is provided in the links below as is information on reporting of detected impact flashes to NASA's lunar meteorite impact program. For use in LunarScan, avi files are segmented into 1 Gb sequences using the freeware program VirtualDub (see http://virtualdub.sourceforge.net/ ). To exclude satellites or space debris as causes of a detected flash it is helpful to refer to satellite mapping programs such as Satellite Toolkit or the equivalent.
KIWI OSD Time Encoder with Garmin 18 LVC GPS Unit:
Set up for Lunar Meteorite Impact Imaging:
The setup shown uses a Hartmann mask and F/6.3 focal reducer. The 9.25 inch F 10 SCT becomes a 5 inch F 6.3 SCT. The Hartmann mask is used to slightly defocus the lunar surface so that an impact flash will be recorded as triplet flashes that are slightly defocused and adjacent to each other. Flashes caused by hot pixels and cosmic rays will not be affected by the Hartmann mask and will appear as single point sources. There are disadvantages to this method, but for a single observer it has the effect of verifying a real flash. The Watec 120N camera, Canopus framegrabber, and KIWI OSD time encoder with GPS attached are shown.
Key links for more detailed information on lunar meteorite impact monitoring:
www.glrgroup.org/lunarimpact/manual.htm
www.lpl.arizona.edu/~rhill/alpo/lunarstuff/lunimpacts.html
www.nasa.gov/centers.marshall/news/lunar/index.html
www.gvarros.com/lunarscan.zip
Kiwi GPS time encoder for video:
www.pfdsystems.com/kiwiosd.html
