NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Not exactly Navigation, but close...
From: Frank Reed
Date: 2008 Apr 18, 03:28 -0400
From: Frank Reed
Date: 2008 Apr 18, 03:28 -0400
Robert, you wrote: "Regardless, a 38,000 km pass by something that poses such destructive potential still seems too close for comfort." Oh, it's definitely a close pass, and it will be quite fun to observe. I've seen two asteroids passing at the Moon's distance, and at a magnification of about 50x through a medium-sized telescope, their motion was apparent in real time. In the case of asteroid Apophis, you won't need a telescope! The article itself had a couple of internal hints suggesting trouble. First, the story of this asteroid has been around for quite a while. It's been well-analyzed by many different people skilled in celestial mechanics calculations (the idea that "some kid" is beating "NASA" is a hint there's something wrong --the science of astronomy is not equal to NASA). The flyby orbit was worked out in some detail and it's well above the plane of the equator, so there are very few satellites that it might potentially impact. In addition, though there are lots of satellites in geosynchronour orbit, to paraphrase the Hitchhiker's Guide to the Galaxy, "Space is big, REALLY big". It's just damn tough to run into something out there without trying. Additionally, if you do hit a satellite, so what? Their masses are puny compared to a solid mass a thousand feet across. The article said that the object would "become" a ball of iron a thousand feet across on impact. No, it IS a ball of iron (and/or rock). The article also mentioned that the asteroid would impact the Atlantic Ocean. Now if they are only estimating odds of impacts, and even those supposedly revised odds were 450-to-1, then the best you could do is say that it would impact one hemisphere of the Earth, along some band. It would not be possible until much closer to impact to narrow it down to the Atlantic (except in one special case). Finally, in the article that Peter referenced, I see that one of the celestial mechanics specialists identified as verifying NASA's calculations was Aldo Vitagliano. That brings us nicely full-circle back to NavList. His software, Solex, has come up on the list before, and I used it as a tool to generate some ephemeris data for my online lunar distance calculating tools. I recommend it for any of you interested in very high accuracy almanac calculations. Get it here: http://chemistry.unina.it/~alvitagl/solex/ He also frequently collaborates on astronomical calculation projects with Jean Meeus, which is a familiar name to many folks on the list (try googling "Vitagliano" and "Meeus"). -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---