SETI [ASTRO] Radio Meteor Alert


Larry Klaes (lklaes@bbn.com)
Tue, 29 Jun 1999 09:22:27 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Mon, 28 Jun 1999 20:08:45 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] Radio Meteor Alert >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > > >http://science.nasa.gov/newhome/headlines/ast28jun99_1.htm > >Radio Meteor Alert >Marshall Space Flight Center > >Earth may be headed into two meteoroid swarms near the end of June. Ham >radio operators can monitor the action, which may be invisible to the naked >eye. > >June 28, 1999: In June, 1998, meteor watchers observed an outburst of >shooting stars from the constellation Bo÷tes. The "June Bo÷tids" are a >well-known annual meteor shower that usually produce just a few visible >meteors per hour, but in 1998 the hourly rate soared to over 100! Although >no one knows what caused the outburst last year, meteor organizations are >alerting their members to watch out for a repeat performance around June >27-28, 1999. > >As if one meteoroid swarm weren't enough, the earth might be headed into >two. The International Meteor Organization has issued an alert that a >"resonant swarm" of meteoroids predicted by Dr. David Asher in 1993 could >produce an outburst of Beta Taurid meteors in late June and early July 1999. > >Above, right: Meteor enthusiast, Stan Nelson of Roswell, NM, captured from a >meteor on June 27, 1999. He used an ICOM R8500 communications receiver to >monitor 217 MHz transmissions from the Navy Space Surveillance Radar located >in Lake Kickapoo, TX. > >Both showers will be difficult to see visually. The full moon will outshine >most June Bo÷tid meteors, and the Beta Taurids are most active when the sun >is above the horizon. Ham radio operators have the best chance of >successfully monitoring these showers. > >Data reported yesterday to >Data reported yesterday to Science@NASA by an experienced radio meteor >observer, Stan Nelson in New Mexico, suggests that enhanced meteor activity >may be ongoing as of June 27, 1999. > >"My neighbor and fellow astronomy enthusiast, Russ Lockett, and I monitored >217 MHz radar returns for meteors this morning [June 27, 1999]", said >Nelson. "We started at 5:15 am. MDT and noted 46 'blips' by 6:15 am. It was >very active session and ... most of the returns appeared to be typical >meteor signatures." > >It's impossible to say whether the echoes observed by Nelson were meteoroids >from the Beta Taurid stream or from the June Bo÷tid stream. They could be a >mixture of both. > >Beta Taurids >The Beta Taurids are an annual meteor shower belonging to a class of >"daytime showers" that peak after sunrise. (The International Meteor >Organization lists a about dozen daylight meteor showers that are monitored >almost exclusively by radio observations.) The Beta Taurids are usually >active between June 5 to July 18. They emanate from an average radiant of >RA=5h18m, DECL=+21.2 deg and exhibit maximum activity around June 29 (Solar >Longitude=98.3 deg). This year the radiant is just 10 degrees west of the >Sun on June 28, so it is unlikely that visual observers will be able to see >many of these shooting stars. The maximum hourly rate typically reaches >about 25 to the eyes of radar. > >"To identify what happens with the Beta Taurids this year, whether a swarm >event or not, I would suggest radio observers should be especially alert >between June 18-19 through to July 2-3 at least," says Alastair McBeath, the >vice President of the International Meteor Organization. "Still later in >July might be better, as some earlier results suggested a Beta Taurid >maximum around July 2 or 3; this has not been found in data from the 1990s >so far, however." > >The Beta Taurid radiant is above the horizon between roughly 03-04h local >time to about 18-19h, for northern hemisphere sites between approximately >35-55 degrees north near June 28. > >The June Bo÷tids are typically active from June 27 to July 5 with a maximum >that falls on the 28th. Normally it is a very weak shower. The greatest >activity levels reach 1 to 2 per hour only, but the June Bo÷tids are >remembered for strong displays in 1916, 1921, 1927, and most recently in >1998. The radiant, which is near the constellation Bo÷tes at RA=14h52m and >DECL=+58 deg, is above the horizon from about noon until 6 a.m. for >mid-latitude sites in the northern hemisphere. Normally the best way to >observe the June Bo÷tids would be visually, by simply going out and looking >up. However, this year the bright full moon will make visual observations >very difficult, so the June Bo÷tids like the Beta Taurids are best observed >by radio methods. > >Nelson's observation of 46 radio pings per hour was recorded when both the >Beta Taurid and June Bo÷tid radiants were low on the horizon from his >observing site. Either or both of the two showers could have been active >during Nelson's observing session. Ham radio operators can make an important >contribution to scientific understanding of the Beta Taurid and the June >Bo÷tid meteoroid streams by observing these showers as often as possible >through early July. For hams unfamiliar with radio meteor observing >techniques a brief tutorial is given below. Results may be transmitted to >Dr. Tony Phillips and they will be forwarded to the appropriate scientists >and meteor observing organizations. > >How it's Done >If you're interested in detecting radio meteors, the procedures are >relatively simple. You'll need a good commercial radio receiver and an >aerial. Although meteor trains can reflect radio waves at almost any >frequency, the best frequencies to try are usually between 50 and 120 MHz. >Many observers use a common FM radio tunable between 88 and 108 MHz and a >Yagi FM/TV antenna. During a meteor shower tune your receiver to a distant >transmitter between 200 and 1000 miles away. Commercial radio stations, TV >stations, and radar transmitters are all suitable if located at the correct >distance. Under normal circumstances the transmitter should be difficult or >impossible to detect, but when a meteor intervenes the signal hops over the >horizon and a brief fragment of the transmission can be heard. Depending on >the type of the transmitter it might sound like a tone, a bit of music or >voice, or simply noise. Contact lasts for as long as the meteor train >persists, usually from 100 milliseconds to a few seconds. > >Stan Nelson's echo, above, was obtained at 217 MHz which is usually >considered to be a poor frequency for meteor observations. However, the >tremendous power of the Naval Space Surveillance radar (NAVSPASUR) more than >compensates for its less-than-optimum transmission frequency. NAVSPASUR is >an excellent transmitter for meteor observers across the southern United >States. For more information about meteor observing with NAVSPASUR, please >see the Dec. 1998 >see the Dec. 1998 Science@NASA article The Ghosts of Fireballs Past. To >learn more about radio meteor observing in general, see the North American >Meteor Network radio meteor tutorial: >http://web.infoave.net/~meteorobs/guidechap5.html >



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