CoS 108
Published on Jun 26, 2009 at 11:20 am.
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Filed under blogging.
I’ve been busy with summer school and other faculty duties, so I’ve gotten behind in blogging. I am doing a star party tomorrow ( June 27) at Dinosaur Valley State Park. It’s going to be a hot one (temperature wise, with highs over 100 predicted). If you want to read blog entries, though, for the past week, then go over to Starts With a Bang blog, where the 108th edition of the Carnival of Space.
-Astroprof
KAGUYA’s last images
Published on Jun 20, 2009 at 3:36 pm.
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Filed under moon, space exploration.
Japan’s KAGUYA (formerly SELENE) probe crashed into the surface of the Moon as planned this past week. Like many space probes to the Moon, the last action commanded from Earth was to crash into the Moon. This is in part a safety move to make sure that the dead spacecraft does not pose a hazard to any later lunar missions. However, it is also an opportunity to scrape one last bit of scientific data from the spacecraft. The spacecraft crashed into the Moon very near the Moon’s south pole. This is a very important and very poorly studied region of the Moon. The dynamics of orbits means that it is easiest to send a spacecraft from Earth to orbit the Moon nearer the Moon’s equator. Polar orbits are tougher. So, the Moon’s polar regions have been the least studied. Yet, there is reason to suspect that comet impacts on the Moon may have temporarily enshrouded the Moon in water vapor over the history of that body. The floors of deep craters in the Moon’s polar regions might never see sunlight. Thus, those crater floors would be cold — very cold. Any water vapor drifting into those craters would freeze to the surfaces there. In the lab, I’ve used devices called cold traps in vacuum systems. These traps are simply metal plates that are in thermal contact with a reservoir of liquid nitrogen (or some other cryogenic substance). Though the pressure in the vacuum system is near zero, there is always a little gas left. As the gas molecules in the system (water vapor, grease outgasing, residual atmosphere, etc) contact the metal plates, they tend to stick. The pressure in the system drops as more gas is removed by the cold traps. A very similar thing may happen in the craters in the Moon’s polar regions. At least, that is the theory.
I remember being at a conference when the radar data from the Clementine mission suggested that perhaps some of that water ice had been found in the lunar polar craters. Then, over a year later, it hit the public airwaves, with news reporters suddenly jumping on the news. There was a special Nightline segment on the discovery of lunar polar ice. My students were sort of dumbfounded, asking me what all the news was about. After all, didn’t I just tell them the same thing earlier in the semester? Hmm. But, the news media went a bit overboard, in my estimation. They made the ice deposits out to be giant lakes of ice. Sadly, some astronomers jumped on the same bandwagon. Then, there was talk of the giant lakes of ice being reservoirs of water that would support moonbases and colonies.
Now, I can’t say for certain that there are not giant lakes of ice in those craters. However, that is not how I envision any ice there. For one thing, more rocky meteors that icy comets likely hit the Moon. Even the comets are not composed 100% of ice! The Moon itself is a rocky body, and anything big hitting the lunar surface fast enough will pulverize the ground and send rocky debris everywhere. There will be a lot more dust and dirt tossed around than just water vapor. So, I’d imagine that the water vapor drifting into the craters might result in some sort of deposit like a thin frost at best. Now, if all that happened was that the frost was added to over the years, then you might wind up with a lake of ice. But, what about all of the other dust and rocky debris? That gets tossed into the craters, too. And smaller meteorites slam into the craters and churn up the surface, volatilizing some ice and burying nearby ice with dust. So, I always thought of the ice in those craters to be a mixture of ice and dust, more like permafrost than like a frozen lake. Granted, this is not my field of expertise, so I could be wrong on this.
Since the Clementine data, several spacecraft have slammed into the Moon. None have kicked up measurable levels of water. KAGUYA is the latest to run into the lunar surface, and we’ll have to wait to see the data collected by astronomers studying the ejecta of the impact. So far, though, the results are consistent with what I would expect. It would be exciting to find pools of frozen water on the Moon, but I really don’t expect that to happen.
But, as KAGUYA plunged to its end, it was busy sending back images of the lunar surface. I’ve reproduced a few of them here for you (one at the top of the post, and the rest below). These are very high resolution images — some of the best showing the lunar surface from a spacecraft. They show a rugged and foreboding terrain. The impact site was in the shadow, so the last few images are mostly black, with just the tips of crater ridges and mountains lit by the Sun. This is typical of the terrain that I have seen from this part of the Moon. Even if there are giant pools of frozen water in these craters, it would be very difficult to reach the ice. Landing a manned craft on the Moon is tough enough under the best of circumstances. Landing in this terrain would be very difficult. There are very few flat and level places to land. Even a lunar surface vehicle would have a tough time making it across this terrain. So, I am not so sure that a moonbase or lunar colony would really be able to get to any ice deposits here (at least not with our current level of technology).
Though these were the last images sent back by KAGUYA, they are very important. This part of the Moon seriously needs more research, so planetary geologists will be pouring over these images looking for clues to the nature of the Moon’s surface in this area. I am looking forward to hearing their findings.
-Astroprof
Images courtesy JAXA/NHK
CoS 107
Published on Jun 14, 2009 at 1:53 pm.
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The 107th edition of the Carnival of Space is now live over at Innumerarble Worlds blog. Go over there and check out the collected entries from the space blogosphere. My very busy academic year continues with heavy summer teaching load.
-Astroprof
KAGUYA plunges into the Moon
Published on Jun 10, 2009 at 10:05 am.
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Filed under moon, space exploration.
The KAGUYA (formerly SELENE) spacecraft is at the end of its mission. As with several other recent missions to the Moon, KAGUYA’s final action will be a deliberate plunge into the lunar surface. The orbit has already been altered, and at this late time, there is not much that could stop it from slamming into the Moon. JAXA, the Japanese space agency, has released a map showing the anticipated impact site (reproduced here).
The impact will be near the far southwestern limb of the Moon (as seen from Earth). The impact time will be 18:25 UT (that is 1:25 pm Central Daylight Time here in the US). When the probe hits the Moon, it may create a flash or small plume. JAXA and astronomers are interested in any observations of anything that anybody sees. At the time of impact, though, the Moon will not be visible from here. In fact, it will be on the opposite side of the world. Observers in Asia, Europe, Africa, and Australia will have the best view. In fact, I’d imagine that India and Australia would be in prime position, with the Moon high in the sky at the time. I don’t expect any flash or plume to be visible in binocular, and certainly not with the naked eye. Most likely, you’d need at least what would be a medium or large amateur astronomer sized telescope to see anything.
This is not the first time that spacecraft have slammed into the lunar surface. In fact, the first spacecraft to reach the lunar surface, the Soviet Luna 2 spacecraft, did just that on September 13, 1959. Since it is easier to just run into the Moon than to try to land on it, the first American spacecraft to the lunar surface (the Ranger program) also was designed to crash into the lunar surface, a maneuver refered to as a hard landing. Ranger 4 was the first to actually accomplish this, on April 26, 1962. Ranger 4 ran into the far side of the Moon, making it impossible for data to be returned to Earth. Actually, the spacecraft had failed and was sending little data back, so it really would not have mattered. The first Ranger to actually run into the Moon with the cameras running and sending information back to Earth was Ranger 7, which impacted on July 31, 1964.
The first attempts to reach the lunar surface were hard landers because that is easier than trying to land intact. Eventually soft landings occurred, too, of course. But, you can learn a lot from studying a body from orbit. So, many missions to the Moon were placed into orbit around it. In the 1960s, both American and Soviet unmanned spacecraft were placed into lunar orbit. At the end of their missions, the American spacecraft were generally given a command to plunge into the Moon. Many of the Soviet spacecraft continued to orbit until the spacecraft was no longer functioning. This was a point of contention between the two respective nations and their space programs. After all, NASA was in the midst of a very public race to land men on the Moon by the end of the decade. The Soviets were also trying to send men to the Moon, but their manned lunar program was not progressing as well as the American one, and ultimately failed. There was some concern expressed that all of the orbital debris around the Moon from leftover spacecraft could pose a hazard to the Apollo missions. The concern was further compounded by the fact that there was no way to reliably track spacecraft in lunar orbit once they had ceased to transmit. It was hard enough to track Earth orbiting space debris. But, the Moon was simply too far away to be able to track of all of the debris orbiting it. The Soviets, of course, pointed out that the likelihood of one of the handful of old spacecraft orbiting the Moon hitting anything else was extremely small. Still, this was a point of contention between the two nations (one of many in those days).
Soon after the end of the Apollo missions, the Soviets quit sending Luna spacecraft to the Moon, too. For nearly two decades the Moon received very little attention. Things changed, though, with the Navy’s Clementine spacecraft. A testbed for technology, the Clementine mission used instruments that revealed a great deal of detail on the Moon, and renewed scientists interests in that nearby world. A startling finding, though, was that radar reflected from some of the craters in the southern polar region of the Moon that seemed to indicate the possibility of ice on the Moon. The discovery is significant, because the Moon rocks brought back by the Apollo astronauts show that the Moon is amazingly deficient in water. The ice in the polar regions would presumably be the result of trapped water vapor resulting from the impact of comets on the lunar surface. Ice on the Moon may have been somewhat unexpected, but it wasn’t totally surprising. A few years earlier, the Arecibo radio telescope had found similar deposits in the polar craters of Mercury. Still, the finding was something significant.
So, when NASA sent another spacecraft to the Moon in 1998, the Lunar Prospector, one of its goals was to look for evidence of ice in the polar craters. Lunar Prospector failed to find the ice that the Clementine data suggested. At the end of the mission, the Lunar Prospector was deliberately crashed into the lunar surface into one of the craters that was suspected of having ice in it. The hope was that a cloud of material spit out by the impact would show the spectral signature of water. However, water was not found. Later missions have continued to look for ice in the southern lunar craters, without finding the large amount that had been hoped for. Further radar studies of the Moon suggest that the radar data from the Clementine mission may have been misinterpreted, and that large deposits of ice may not exist on the Moon after all. But, the hunt for possible ice still goes on.
More recently, the European SMART-1 spacecraft also plunged into the Moon on September 3, 2006. Rather than slamming into a polar region, though, SMART-1 crashed into the face of the Moon in a spot visible from Earth. Large telescopes on Earth were able to observe the flash of the impact, and the impact site itself has been subsequently studied. The impact site is an artificially created crater, exposing fresh material onto the surface of the Moon. Much of the surface material has been slightly altered by eons of exposure to the Sun and cosmic rays, so this gives an opportunity to see lunar material that is fresh.
Like these recent missions, the impact of KAGUYA is seen as not only getting rid of space debris, but an opportunity to study the Moon by observing what gets thrown out by the impact itself. This is a very clever way of disposing of an old space probe, using the kinetic energy of the body of the fast moving spacecraft to excavate material.
-Astroprof
Image courtesy JAXA
June and July Star Parties
Published on Jun 9, 2009 at 8:28 pm.
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Filed under observing.
For many people, summer is a time to get out and do things. Many amateur astronomers like to observe in the winter because the skies are often clearer, darker, and the nights are longer (permitting more observing and observing starting earlier). Serious amateur astronomers know how to dress for cold weather. However, for most other people, the summer months are when they think about doing such things. So, this summer, I am helping the Texas Department of Parks and Wildlife host two star parties at Dinosaur Valley State Park. For those of you who are not familiar with the term, a “star party” is a night of observing the sky. I typically start the event with a public lecture once it gets dark enough to see the projector. Often I have friends who are amateur astronomers come with their telescopes. I bring either a couple of my telescopes or some of the college’s telescopes. By the time I finish talking, it is dark enough to see things in the sky, so we observe for a while. The event is free (other than the standard park admission) and open to everyone.
The dates for the star parties this summer are June 27, 2009, and July 18, 2009. Sunset occurs about 8:42pm on June 27 and 8:37pm on July 18. So, I’ll be starting talking soon thereafter. It won’t be dark enough to do much viewing until after 9pm both nights. Usually my pre-observing talks say a bit about what we will be observing, and a bit about some other topic. The July 18 star party will be right before the 40th anniversary of the Apollo 11 landing on the Moon, so naturally that will be focus of that talk. So, if you are in this part of Texas on those nights, think about dropping by.
-Astroprof
CoS 106
Published on Jun 7, 2009 at 11:26 am.
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Filed under blogging.
The 106th edition of the Carnival of Space is now up at the Next Big Future blog. This week’s carnival has 28 blog entries gathered from the spacey bloggers around the blogosphere. So, go check out the links. The topics include astrophotography, meteors, new moon maps, and interstellar spacecraft engines.
-Astroprof
The Moon and Antares
Published on Jun 6, 2009 at 1:41 pm.
1 Comment.
Filed under observing, skywatching.
As the Moon goes around the Earth, it naturally passes in front of various stars now and then. The heavens are full of stars, so this is a pretty normal occurrence. When my students are doing their moon observations through the telescope, I often look to see if a star is near the limb (the astronomical term for the visible edge) of the Moon. I have the students watch to see if the Moon is getting closer or farther from the star over the course of the lab. Once in a while, we get lucky. As we are watching the Moon passes in front of the star. This is called an occultation. Most of the stars that are occulted, as I said, are pretty dim. Once in a while, though, a really bright star is occulted. That is happening tonight. The Moon will pass in front of the star Antares (the brightest star in the constellation Scorpius). Antares is a rather distinctive star. It is one of the stars that has a noticeable color. It appears orange or reddish. In fact the name Antares means Rival of Mars. The star Antares is about the color and brightness that Mars typically appears in the sky.
Antares is a quite bright star, easily visible with the naked eye. Normally, that makes an occultation very easy. However, the Moon will be very nearly full, and that will complicate the matter. I’d suggest using a pair of binoculars if you want to observe the event. If you want to observe the event, you ought to look up when it will happen for your particular location. That will vary a little from place to place. The International Occutation Timing Association has a web page dedicated to this particular occultation, and it has the needed information. One word of caution, though, about using that web site. The times given are Universal Time. That is NOT the time that your clock reads. You will need to find out how far your local time varies from Universal Time, which is the local mean time at the Prime Meridian (often called Zulu Time or Greenwich Mean Time). For here in Fort Worth, the dissapearance will occur at 01:53 UT. That is 8:53PM Central Daylight Time (what the clock reads). This will be a very difficult event to observe. You will need to be in exactly the right spot, because the Moon will be only about 7 degrees above the horizon. That is quite low, so you must find a spot where you can see the eastern horizon and catch the Moon before the event happens. It will have just risen about half an hour before it passes in front of Antares. The star, itself, will rise immediately after the Moon. In binoculars, you would see something like the following image right before the occultation.
The entire event will occur during twilight, so you might have trouble seeing Antares without binoculars. For observers farther east, this will be much easier to see. Florida and the entire east cost of the US should have a wonderful view. Unfortunately, observers in Europe are not properly placed to observe the occultation, though they will see the Moon passing very close to Antares. Observers in the western United States miss out because the Moon will not have risen at that time. Part of Canada (south of Hudson Bay) see the occultation. The rest of Canada misses the event, though. They will see the Moon pass right by Antares, in an event known as a conjunction. Central America gets to see the entire event, though, as does the northern part of South America. Most of South America sees a conjunction on the opposite side of the Moon from what Canada sees. Observers in the Carribean probably get the best view.
But, the Moon keeps moving, and it eventually moves out from in front of Antares. This will occur after the end of twilight here, as seen in the following image.
Here in the Fort Worth area, the reappearance will happen about 03:08 UT (that is about 10:08 CDT). At this time, the Moon will be 19 degrees above the horizon, much easier to observe. Still, I think that binoculars will help the observing because Antares will be appearing on the more lit side of the Moon (remember, it is just before full).
I always like observing occultation events. It is dynamic, and you actually get a chance to observe that things are moving in the sky. If you get a chance, go out and look for the event (especially if you are in Central America, northern South America, or eastern North America).
-Astroprof
Images created using Stellarium software
