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Home > News > Mark Your Calendars - LCROSS Lunar Impactor Plume to be Visible from Earth
Based on the latest analysis of available lunar data, NASA selected the Cabeus (proper) crater as the LCROSS impact site (labeled SP-C on the map). The decision was based on continued evaluation of all available data and consultation between members of the LCROSS Science Team and the scientific community, using the latest observations from the Lunar Reconnaissance Orbiter (LRO), Lunar Prospector (LP), India's Chandrayaan-1, and JAXA's Kaguya spacecraft. This decision was based on the team's best understanding of hydrogen concentrations in the Cabeus region. While the ejecta does have to fly to higher elevations to be observed from Earth, a shadow cast by a large hill along the Cabeus ridge, will provide an excellent, high-contrast, back drop for ejecta and vapor measurements. During the last days of the mission, the LCROSS team will continue to refine the exact point of impact within the Cabeus crater to avoid rough spots and to maximize solar illumination of the debris plume for better Earth observations. (Image Credit: Ames Research Center, NASA)
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The LCROSS mission is a search for water on the Moon. This will be done by sending a rocket crashing into the the Cabeus crater near the south lunar pole, causing a big impact and throwing tons of debris and potentially water ice and vapor above the lunar surface. The impact will release materials from the lunar surface that will be analyzed for the presence of hydrated minerals, which would tell researchers if water is there or not.
The two main components of the LCROSS mission are the Shepherding Spacecraft (S-S/C) and the Centaur upper stage rocket. The Shepherding Spacecraft will guide the rocket to the Cabeus crater, which has been selected because it has a high probability of containing water.
The Shepherding Spacecraft and Centaur rocket were launched together with another spacecraft called the Lunar Reconnaissance Orbiter (LRO). All three were connected to each other for launch, but then the LRO separated one hour after launch. The Shepherding Spacecraft has guided the Centaur rocket through multiple Earth orbits, each taking about 38 days. On Friday, October 9th, the rocket will separate from the Shepherding Spacecraft and impact the Moon at more than twice the speed of a bullet, causing an impact that will result in the big plume of lunar debris. While this is happening, the Shepherding Spacecraft, which has scientific instruments on-board including cameras, will be taking pictures of the rocket’s descent and impact into the Moon. Four minutes later, the Shepherding Spacecraft will follow almost the exact same path as the rocket, descending down through the big plume and analyzing it with special instruments. The analysis will specifically be looking for water (ice and vapor), hydrocarbons, and hydrated materials. The Shepherding Spacecraft will be collecting data continuously and transmitting it back to Earth before it too crashes.
We should be able to view the resulting plume of ejected material with a good amateur telescope. Unfortunately, the Daybreak will prevent viewing of the debris plume from the Eastern US time zone. For the Central time zone, the best viewing will be west of the Mississippi River. Mountain and Pacific time zones will have excellent lighting conditions, as will Alaska and Hawaii.
NASA has posted a very comprehensive FAQ section for the LCROSS mission (see below for the FAQ link). Here is a summary:
OBSERVATION:
Q: What will I be able to see?
A: All of the following is based on an assumed earth visible ejecta cloud rising to 10 Km above the lunar surface and crater wall. Impact design location is to maximize the amount of this in sunlight, but variables here will determine how much of it is actually illuminated. At 385k Km away from earth the 10Km impact event will be approximately 0.001488 deg. (5.36 arc sec) or about one quarter of one percent of the moon's dia. (for reference, pretty small, but if you slice the moons diameter up into 100 strips, you can get the idea).
The brightness or magnitude of the event is of course dependant of what part you are talking about, but we estimate magnitude 6-9 for the best visible part and time. Depending on where we actually hit, there should be an approximate sun mask of 2 km., meaning the impact plume needs to rise up that far before the sunlight hits and illuminates it. Note, brightness falls off very quickly above that altitude, and the event will be V shaped.
So, if you have an eyepiece that comes close to being filled up with a full moon, no matter what size telescope you have, this event will be a very small portion of the field you will be looking at. Other than higher magnification, the main advantage of a larger telescope is the greater light gathering capability. So while small, the event has a better chance of being observed in a larger telescope because the larger telescope has a better ability to see low brightness objects.
Q: Where do I look?
A: South pole. For most small to medium telescopes, this is where you need to point. If you can magnify sufficiently to zero in on the general crater area, then go to this site now for a good description of where to look and note again.
Q: I live in Texas. Will I be able to see this event?
A: Yes, but it will be just starting to get a bit light out. Impact time for your time zone is 6:30 a.m., and Sunrise is at about 07:30 a.m. This will still be reaasonably dark/early dawn which complicates viewing of low light events a bit but it still should be possible if you can keep your eyes dark adapted as best you can. East of the Mississippi will be more of a problem due to the rising sun making it very light out. Viewing through the telescope however, you should still see reasonably dark background behind the moon, so it still may be OK. East coast viewing is even more difficult because the sun will be up. When it's this light out, 'dark adapting' your eyes is very difficult when trying to see something of this low brightness.
Remember:
1) This event only lasts a couple minutes. Timing is key. Be ready. Know where to look and give your eyes some time to 'dark adapt' prior to impact time.
2) If you are watching through a telescope, you've only got one eyepiece. If there are a number of friends and neighbors out viewing using just the one telescope, it will be tough to share 2 minutes between 5 to 10 people. Suggest also having the website up or going to an event that can project the impact event for many people to view. Star parties are great because of the large number of scopes out, and you'll easily hear when the folks with the bigger scopes see the event, but the same people-to-eyepiece ratio can exist (and may be even worse).
3) This event is short (20-120 sec. for best part) and dim (magnitude 6-11 for brightest part).
4) This event will be relatively dim and hard to see, particularly in relation to the very bright moon that you will be looking at and whose bright terminator is so very close. Do your general moon crater viewing in advance and then move your eyepiece view to mostly darkness on the south pole and let your eyes adapt for a couple of minutes prior to impact. Keep the very bright sunlit surface of the moon out of the field of view as much as possible -- you will get a much better experience of this low brightness event.
TELESCOPES/OPTICS:
Q: What kind of telescope should I use to see this?
A: This will be a 2-5 minute event. For a 10 inch to 12 inch diameter scope, you'll want eyepieces in the 4-8mm range for this event.
Q: Can I observe this event using binoculars?
A: No. In general you'll need at least 200x magnification, and maybe only possible with 300x and above. More importantly, you will need the greater light collecting capability of a large aperture optic. Even some of the larger binoculars (25x by 125mm) still won't do the job. Zoom binoculars (such as 10x-40x by 80mm for example) at maximum zoom (2mm exit pupil in this example) are great for very bright terrestrial viewing of birds and hangliders during bright daylight viewing, but are not useful at that magnification for low light viewing which is required here.
Q: I have an old 6-inch Newtonian with a reasonably good mirror. What are my chances?
A: Not great.
Q: I have an 80mm refractor. What are my chances?
A: Refractors of that size are great for clear and sharp viewing of wide stellar fields, but this size does not have much magnification capability which is needed for viewing such a small event as this.
IMPACT:
Q: How fast will the LCROSS impactor be going when it hits?
A: Approximately 2.5 km/sec or 5592 miles/hr.
Q: Viewing through a good size telescope (20"), will I be able to see the impact itself, or the 'flash' created by it?
A: Most probably, No, but with a caveat. The impact is designed to occur on a permanently shadowed crater wall (facing away from the sun and generally us as well), and is not expected to create enough of a 'flash' as to be seen on opposite crater walls (which may or may not be sun illuminated at the time). Seeing the flash from earth however is more likely than seeing the impact itself (possibly viewed only by the LCROSS shepherding spacecraft). Targeting accuracy however may not be sufficient for a guarantee of this type of a hit, so the possibility (we'll say low probability) does exist for a viewable impact or flash if the centaur hits at a spot that is directly viewable from the earth.
Q: How high will the impact plume actually go?
A: Depends a bit on what we consider the 'plume' to be. For us, we're interested in visible light spectrum. Best visible brightness for small scopes on earth is estimated somewhere in the lower altitudes at the 30 to 90 second event time. We're guessing 8-15 Km altitude for the brightest part of the event which is what amateur observers might expect to be able to see. The 'plume' will be bright at first as soon as it rises into sunlight (estimating magnitude 7 to 9), but will fade in brightness quickly as it grows in altitude.
IMAGING:
Q: What's the best way to image the impact event?
A: A digital astro camera mounted to a reasonably large telescope. These are not SLRs. Folks with these setups have a good idea already on how best to image this event.
Q: Can I use my digital camera to capture the impact?
A: It may be possible, but it won't be easy -- Use focal plane or eyepiece projection through a sturdy, tracking mount. Biggest problem after setting this up may be focus and timing. Practice with your setup ahead of time if possible. This may only work with multiple pics 'stacked' together. Main problem with stacking a number of pics is you must take a series of them which (unless you have multiple optics to use) will take up all your viewing time, and you may miss the whole thing. Also, watching the event through a camera viewfinder may limit what your eyes can see, and won't be possible when the shutter is actually open. It's a choice you have to make, as you don't have much time to both image and view with your eyes.
Q: What kind of exposures should I use?
A: Again, 35mm or digital SLR pics are not likely to succeed with this dim and quick event. Generally, you'll want to use the highest ISO your camera can handle without producing too much noise. Use dark frame subtraction (post session if possible or you'll loose half your viewing time), and a number of exposures -- preferably stacked in some fashion. While a good exposure of the full moons bright surface might be F/8 at 1/250th sec at ISO 100, this will be much, much dimmer than that -- on the order of many stops. In fact, when imaging a magnitude 8 galaxy, exposures of many minutes to an hour are often used.
Main problem here is a low light, moving object and 1 minute of available exposure time -- very hard to image without specialized equipment. Experiment now if you don't already have a good idea.
Q: Can I get pics of this event using my digital camera 'piggybacked' on a telescope with tracking?
A: Generally, no. The event would be about the size of a pin head on a kitchen table. You'd need a very large (huge) focal length lens (a lens combination with 3000mm on a 35mm film camera only gets you about 60x magnification. Digital cameras with the smaller chips get you an effective boost of about 1.5 times this for a given lens, but you're still barely getting to 100x mag) to get the needed magnification. Advantage though is you can blow up a good resolution/high pixel digital photo & maybe get a good result with some software manipulation. If you do try, make sure the tracking is good and your scope is used to carrying the camera and large lens weight so the tracking stays on track. Eye-piece or direct projection would be the preferred method when using a normal digital camera. Short focal length 'reflector' lenses, while small and light, are not recommended. Better yet are the digital astro-cameras with a huge lens.
Q: I have been using a astro video camera attached to my scope to obtain many images of planets and then stacking them for a final image. Can I use this technique for imaging the LCROSS impact.
A: Possible, and with the right camera and setup, this may in fact be the best way to both capture this event as well as potentially show it to many people at once. Not sure on this one. Biggest unknown here is can the individual cam frames capture the low brightness of this impact event. Will likely require a camera that is very good at low light -- not all are -- even ones used for planet imaging. Best is to test on low light objects and set up viewing session accordingly. Also suggest (if not already familiar) making sure you use it and practice with the eyepiece you'll be using, making sure the scope tracking will not be a problem -- You've likely already made yourself familiar with these variables. If the event is bright enough, suggest capturing and stacking 10 to 40 images in sets and making a series of them to create a semi-video sequence.
Q: What about just a time lapse digital photo taken through a scope?
A: A time exposure (5 to 30 seconds for example) through a good size scope may make an interesting pic or series and will capture/integrate more of the low light event. You also won't loose any or as much time as you would between many individual shorter frames. Again, make sure the tracking is dead on, and you have virtually none of the sun-lit moon's surface in the shot (very edge only) less you blow out the image you are trying to capture. You'll likely end up with a blur if it works, but it will be something good to see, especially if surrounding terrain also comes through and is reasonably sharp.
For more information:
http://www.nasa.gov/centers/ames/news/features/2009/LCROSS_new_crater.html
http://www.astromart.com/news/news.asp?news_id=958
http://lcross.arc.nasa.gov/mission.htm
http://lcross.arc.nasa.gov/observation/amateur.htm
http://www.nasa.gov/mission_pages/LCROSS/impact/event_index.html
AstroMart News Archive:
http://www.astromart.com/news/search.asp?search=.+&search_btn=Go
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