6 October 2006

I have been reading the book RadioScience Observing by Joseph J. Carr, ISBN 0-7906-1127-9 and made some notes/quotes from the chapter on Detecting Meteors by Radio:

Meteors

Meteors have been called the “driftwood of space” because they are formed from the debris of space. Now that we have a lot of man-made space junk up there, I suppose that not all meteors are natural material. Meteors consist of pieces as small as a grain of dust, or big enough to do some really serious damage on Earth. Some scientists believe that the extinction of the dinosaurs occurred because of a massive meteor hit, probably in the Gulf of Mexico or Yucatan area of Mexico. In Arizona, there is a meteor crater that is a mile wide and 600 feet deep. That’s serious! Incoming meteors have velocities ranging from 11 kilometers per second (km/s) to 72 km/s.

When a meteor hits the atmosphere, it packs a large amount of energy. The energy is given up in the form of friction and ionization of the atmosphere. The friction is great enough to heat the meteor to incandescence, which is seen by us as shooting stars. Oddly, for all the great visual display, only ten percent of the energy is accounted for my friction. The rest is by ionization; unless, of course, the meteor is large enough to hit the earth’s surface, in which case some of the energy is expended, making the ground shudder.

Ionization by incoming meteors occurs as low as 50 kilometers (km) and as high as 150 km, with most being in the range of 80 km to 110 km.

Observing Opportunities

Meteor hits to our atmosphere occur all the time. One source claims that more than 100 million dust-sized particles hit Earth’s atmosphere every day, and many of them are visible. Look into the sky on most nights and you will occasionally see a shooting star. These are meteors. Although meteors impinge Earth all the time, there are several instances every year when the incidence goes up, when a “meteor shower” occurs. Table 13-1 shows the major showers with the peak dates, observation times for 40 degrees north latitude and 55 degrees north latitude [not copied here], and the antenna offset direction for maximum yield [also not copied here].

Table 13-1. Meteor shower data

Shower	Peak	Velocity (km/s)	Rate/Hr	Path	Time (Local)
Quadrantids	Jan 1-4	42	50	NW-SE	0200-0740
				E-W	0740-0900
				NE-SW	0900-1430
Eta Aquarids	May 1-6	64	15	NE-SW	0400-0630
				E-W	0630-0830
				NW-SE	0830-1050
Arietids	June 1-15	39	60	N-S	0600-0745
				NE-SW	0745-0830
				E-W	0830-1015
				NW-SE	1015-1155
				N-S	1155-1425
Perseids	Aug 12-13	61	50	NW-SE	2330-0430
				E-W	0430-0730
				NE-SW	0730-1230
Orionids	Oct 21-22	67	20	N-S	0015-0145
				NE-SW	0145-0350
				E-W	0350-0500
				NW-SE	0500-0700
				N-S	0700-0830
Leonids	Nov 14-18	72	10	N-S	0200-0430
				NE-SW	0430-0600
				E-W	0600-0700
				NW-SE	0700-0840
				N-S	0840-1100
Geminids	Dec 10-14	35	60	N-S	2115-0100
				NE-SW	0100-0200
				E-E	0200-0230
				NW-SE	0230-0330
				N-S	0330-0700