Comments on: The Two 16 Towers

By: Loperspest

Loperspest — Wed, 23 Jan 2008 19:39:19 +0000

1plus8, a relatively well known youtuber, claims that because of the gamma rays produced by the moons interaction with cosmic rays would make a landing fatally hazardous. I want to hear your opinion on this specific claim, if it isn’t to much trouble. I have as yet found little to rebut him on this specific issue.

By: The Bad Astronomer

The Bad Astronomer — Mon, 24 Oct 2005 22:36:23 +0000

Tracer, you’re correct. But lower energies are more like hard X-rays.

There is another instrument called the GLAST Burst Monitor (to look for GRBs) that is sensitive to lower energies, down to a few keV.

By: tracer

tracer — Mon, 24 Oct 2005 21:41:19 +0000

Holy flying bat guano, Batman! The GLAST observatory detects gamma rays via pair production?!

That means it can only detect gamma rays of at least 1 MeV, right? I mean, lower-energy gamma rays won’t have enough oomph to create a positron and an electron. Does GLAST have some other means of detecing those ho-hum garden-variety gamma rays in the mere 100-900 keV range?

By: The Bad Astronomer

The Bad Astronomer — Thu, 20 Oct 2005 16:03:44 +0000

"Interleaved" is similar (if not the same as) interweaved.

By: The Bad Astronomer

The Bad Astronomer — Thu, 20 Oct 2005 16:00:56 +0000

I corrected the resolution; it's actually 0.5 arcmin (I had read an old document yesterday when I wrote "a few arcminutes"). EGRET, the best gamma-ray observatory before GLAST, had 15 arcmin resolution! So this is 30 times better. It sounds bad compared to optical 'scopes, but focusing gamma rays is nearly impossible (which is why most detectors don't try to focus). It's possible that in 10 years we'll have better tech, but for now GLAST is the best we can do.

By: pumpkinpie

pumpkinpie — Thu, 20 Oct 2005 14:46:36 +0000

Thanks for the article! I’m interested in finding out how exactly telescopes work to focus the different kinds of energy and make pics, so now I can cross Gamma Rays off my list!

When you describe the towers, you say “a series of interleaved silicon strips, sort of like wicker.” Is interleaved a term unfamiliar term to me that I’ll have to look up, or did you mean interweaved? (wicker reference.)

By: arensb

arensb — Thu, 20 Oct 2005 14:38:58 +0000

The LAT is accurate enough to pin down the gamma ray location to a few arcminutes in the sky (for comparison, the Moon is 30 arcminutes across).

Does that mean that the LAT can “focus” to within roughly 1/30th of the diameter of the moon? I.e., that at best it can take a 30 pixel by 30 pixel photo of the moon? If so, that doesn’t sound very impressive, and nigh-useless for taking pictures of more distant objects, so I hope I’m misunderstanding something.

Or does the LAT use results from all 16 towers to improve accuracy and focus better? Or is the nature of gamma rays such that even a 30×30 image of the moon is better than astronomers have been able to do so far?