On 9-15-2009, Raf wrote: > hoping in your prediction Raf - here it is. - Kurt ----------------------------------- The following is an amateur note. Comments and criticisms on the same are welcomed. At url - http://members.csolutions.net/fisherka/astronote/observed/LCROSS/20090915LCR... http://tinyurl.com/mqylqf - I have posted another in a series of ongoing discussions between myself and Jim Mosher regarding the expected visibilty of the impact plume. My response to Jim is overlength and goes into some technical matters that may not be of interest to general group readers. Therefore, I have posted by link to a separate text file. My amateur analysis of the plume ends with my conclusions regarding whether the plume can be observed visually and imaged. The extended discussion also concludes with a description of what the plume will look like for amateurs using scopes of 5 inches or larger and with recommended strategies for imaging the plume. The support and reasoning for my conclusions are contained in the linked extended discussion file. Those conclusions and recommendations may be of interest to general readers and I replicate that "conclusions" portion of the extended response below. Clear skies - Kurt ----------------------------- - Conclusions On Sept. 11, Rick Baldridge noted that: "NASA will provide professional and amateur observing groups more detail regarding plume size and visibility in the coming weeks. The plume will not extend above the lunar limb, and will not be situated against a dark background such as a shadowed region between craters. However, that does not mean the plume will not be visible. Video and photographic observations must now focus on bringing out the brightening caused by the eject plume in front of a lit lunar surface." September 11, 2009 LCROSS Science Team Announced Target Crater Posted by rickbaldridge on September 11th, 2009. NASA LCROSS Citizen Science Page Blog http://apps.nasa.gov/lcross/ Implications from the foregoing discussion [in the linked extended discussion file] for imaging the LCROSS impact are as follows. If the ejecta plume follows its predicted apparent brightness _and_ if the mpsas of the shadowed portion of crater Cabeus A1 is at least one magnitude lower than 4 mpsas, the impact can be easily imaged and observed using 5 inches of aperture or more. Earth based amateur observers will see essentially a surface contrast effect. As the brightest part of the 10km plume expands within and above the bowl of 17km Cabeus A1 and reaches a brightness of about 4.0 mpsas, the plume will obscure the shadowed portion of Cabeus A1 from Earth observers. The plane of the rim and/or just above the rim will take on a surface brightness equal the surface brightness of the surrounding surface terrain. That surface typically will have an mpsas between 4.0 and 6.0. Normally, Caebus A1 has a bowl shaped appearance caused by crater shadowing when viewed from Earth visually at 300x and/or when imaged, as illustrated in this high resolution amateur image taken in September by Stefan Lammel: http://tinyurl.com/qjex6e (I visually observed the same view a few hours after Stefan took his image using a Meade ETX 125 with a TMB 4mm planetary eyepiece at 300x. The level of detail that I was to observe visually easily exceed what Stefan was able to capture photographically. Stefan when posting his image accompanied the comment that the Moon was at a low altitude and that it was not his best work.) During the first 30 secs, the brightest part of the ejecta plume will create a contrast effect as the surface brightness of the brightest part of the ejecta plume removes the contrast between the crater shadow and surrounding terrain. For visual observers, the crater may see a blurry mesa effect. Caebus A1 will look like a terresterial mesa or will have a slight "raised muffin" appearance. Where the brightest part of the ejecta cloud crosses the sunlit portion of the lunar surface, it will not be visible due to lack of contrast between the cloud and the lunar surface. For low resolution imagers like myself, the crater will simply "disappear" due to this contrast effect beginning near the 30 second mark for a duration of about 30 seconds and then mysteriously reappear on AVI frames. See my 9-10-2009 image for an example of low-resolution image: http://tinyurl.com/qw32fy Although no images have been gathered that match the libration and illuminated fraction of the impact, the reduction in libration in latitude to -6.0 to -3.0 between now and the impact on October 9 will only increase this contrast effect. The Cabeus A1 crater shadow will be relatively thinner (in arscsecs) on the day of impact as compared to that shown in Stefan's image. Imaging of the LCROSS impact will be a fairly straight forward process for amateurs. High focal length imaging is preferred in order to minimize the percent of the sunlit lunar disk captured in a frame. High focal lengths dictate that large pixel DSLR cameras and CCD cameras are disfavored relative to small pixel sized fast moderate and high-end lunar imaging cameras. See Sinnott's Effective Focal Length to Pixel Size nomogram, url - http://media.skyandtelescope.com/images/Linked.gif - and the more detailed discussion in another message in the LCROSS Observation newsgroup - Post by K. Fisher 9-8-2009 LCROSS Observation Group Efls for imaging the LCROSS impact http://groups.google.com/group/lcross_observation/msg/764ceeede969207a http://tinyurl.com/owkdf7 Pre-impact image calibration is an easy three-step process. The goal of this process is to set the pixel value of the brightest edge of the rim of Cabeus A1 to 75% of your camera's well capacity in ADUs. This should assure that the full range of pixel values that can be captured on a line profile across the major axis of crater Cabeus A1 are recorded on images stored to your disk. First, focus your imaging gear on the target crater without concern for the exposure setting. Second, slew to 2.6 stellar magnitude theta Auriga. On the morning of the impact, the Moon will be between the horn stars of Taurus and just next to 1.7 mag bet Taurus (Alnath). 2.6 magnitude theta Auriga is one of the figure stars of Auriga and is about 11 degrees away. Nearby alternative stars for exposure calibration around 2.5 stellar magnitudes include: zeta Per 2.8mags B0.5V, delta Orion 2.2 mags O9.5II, gamma Gem 1.9 mags AOIV, beta Auriga 1.9 mags A2IV. Take some test images of theta Tau and adjust your exposure setting so theta Tau's brightness peaks at 50% of your well capacity. Note that the preview histogram in some image capture software _does not accurately_ represent what is stored in captured images on a disk. Open the test images stored on the disk and run a profile measurement or histogram on your image of theta Aur using your image processing software so you are sure your exposure setting captures the right amount of well ADUs. Keep this exposure setting and slew back onto the impact target Cabeus A1. Take some test frames and look at some of the raw images on your disk. Use the profile measuring line tool (e.g. one is available in AIP4WIN) and take a profile of the pixels that cross the major axis of Cabeus A1. Now adjust your exposure setting so that high pixel value of Cabeus A1 rim is at 75% of your well capacity. The minimum pixel value shown for the Cabeus A1 crater line profile should also be within the range of a histogram made of the entire test image. You can slightly adjust back from this exposure setting so the Moon is not overexposed _on images stored on your disk._ Again, _do not trust the preview image and histogram_ in your image capture software. Post-image processing will favor software packages that offer region masking like Photoshop. This way individual regions of the bright lunar surface can be supressed in brightness, but pixels that encompass the area within the Caebus A1 crater rim can be selectively stacked and gamma stretched. The impact will provide imagers interested in hobby science with an opportunity to study plume kinematics using photometry measurements from their images. The LCROSS ejecta plume will rise 5 kilometers (5000 meters) to its maximum brightness in about 30 seconds. The vertical plume speed is estimated at an average of 167 meters per second (5000/30). For the first 2 kilometers, the ejecta cloud will be masked from Earth view by Cabeus A1's crater rim. This trip above the crater rim will occur between about 18 seconds after impact through impact + 30 seconds. (30 seconds * 3000 meters / 5000 meters). For the final three kilometers, the plume will be sunlight and the total light from the cloud may have a changing photometric signature related to its vertical travel that will be recorded by amateur video imagers. Such recordings might be examined to extract a plot of the total brightness of the Earth visible ejecta curtain against time. The process for making such a recording and reducing it is generally described as follows. An LPI camera of video that records AVI files including both an audio track and a video track will be needed. For the time signal audio track, the video can be time stamped using a digital metronome as the timed audio source. An inexpensive $30 Ibanez model emits a good sharp tone at a maximum of 180 beats per minute with a different second identifier signal and is available at many local music and guitar stores. url: http://www.ibanez.com/electronics/product.aspx?m=MU40 . Alternatively, imagers can use a more expensive video time stamping rig favored by lunar occulation observers - the KIWI OSDI video-GPS timestamper. url: http://www.pfdsystems.com/ . The NIST WWW shortwave time broadcast is another option for a timing audio signal, but since there is no need to coordinate observations between observers and clear reception of the NIST shortwave signal is usually problematic, the Ibanez metronome may be the better inexpensive no-hassle option. Post imaging, the AVI file is reviewed using movie making software. The individual frames that contain identifable time beats and good images of Caebus A1 are separated. Then each time-stamp identified image is reviewed in image processing software. Most image processing software (such as AIP4WIN) contain a region measuring tool. These tools count the average value of pixels in an identified circular or rectangular area. Use the region measuring tool on each time-stamped image and surround all of Cabeus A1. It will be important to use the same relative pixel coordinates from the center of Cabeus A1 in each individual frame. Note the time stamp and the average pixel value for the uniform measuring region on each frame. Then plot the pixel values against time. Finally, compare your plot against the predicted increases in plume brightness that presumably will be provided by the LCROSS Team. In conclusion, the LCROSS impact can be easily imaged, assuming it reaches the brightness of 4.0 mpsas stated in LCROSS pre-impact modeling. The view may not be as dramatic as one might imagine, but it appears certainly worth trying for. The success of amateur imaging is dependent on the LCROSS Team gathering and publishing for amateur use, the apparent brightness of the surface area around Caebus A1 and the shadowed portion of Cabeus A1 in both mpsas and V stellar magnitudes. If the shadowed floor of Cabeus A1 is brighter than 4.0 mpsas, the impact cannot be observed or imaged by amateurs. By the NASA LCROSS Team calling for amateur imaging and by inducing, through press releases stating that the impact is observable, the public's attendence at private star parties, the LCROSS Team has undertaken the business ethical obligation to gather and publish such photometry data prior to September 27 and before Oct. 9. This ethical obligation is also incured by their dual role as scientists and public governmental employees. September 27 represents the last date in which the south lunar pole will be at 71% illuminated fraction and on which amateurs can make useful "dry runs" of their imaging gear. Advanced amateurs with photometric gear may wish to gather and share their hobbyist studies of the apparent brightness of the shadows of small craters on the opposite east side of the southern polar Moon on September 27. Again, this is an amateur note. Comments and criticisms on the same are welcomed. Clear Skies - Kurt