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	zhr
		is an estimate of the number of shower meteors that would be seen by a single observer, watching an unobstructed area of the sky for a period of one hour, with the shower's radiant at the zenith and a limiting magnitude of 6.5.
		Typically, the ZHR is expressed with error margins, the error being given as +/- ZHR/sqrt(N).
		Our goal is to look at the Geminid rates a Northern Oregon or Southern Washington observer might expect when the radiant is at its highest elevation (~77 degrees) on the morning of December 14 at around 2am PST (10:00 UT).
	skytour.homestead.com /zhr.html (687 words)

	Hourly Rates (Site not responding. Last check: 2007-09-05)
		ZHRs for known meteor showers range from 1 or 2 for the weakest showers that are detectable, to over 100 in the case of the Perseids, Quadrantids and Geminids.
		In 1966, a ZHR of 150,000 was estimated during the 20 minute peak of the Leonid shower.
		When the MPAA film rating system was instituted in 1968 in the U.S., the X-rating was given to a film by the MPAA if submitted to them or, due to its non-trademarked status, it could be self-applied to a film by a distributor who knew beforehand that their film contained content unsuitable for minors.
	www.wwwtln.com /finance/95/hourly-rates.html (1009 words)

	"This November's Meteor Shower" -- skw9811h (Site not responding. Last check: 2007-09-05)
		The zenithal hourly rate (the "ZHR" -- an extrapolation of the average hourly rate of meteors observed to very dark, clear skies with the radiant of the shower at the zenith) is generally only 5 - 20, but this year is different enough to demand more attention.
		The comet responsible for the debris that provides the meteors for the shower, Comet Temple-Tuttle, passed closest to Sun in its 33.17-yr orbit on Feb. 28.
		In 1966, the last time Temple-Tuttle visited the inner solar system, observers in the American southwest saw meteors at a rate of 150,000 per hour with short intervals when the rate was estimated to reach 140 per second.
	www.as.wvu.edu /~jel/skywatch/skw9811h.html (675 words)

	Glossary (Site not responding. Last check: 2007-09-05)
		For scientific comparison purposes, an observed rate is converted to a Zenith Hourly Rate by factoring out local variables such as sky conditions (limiting magnitude), cloud cover and altitude of the radiant.
		Zenith hourly rate (ZHR): An estimated number of shower meteors a single observer would see under virtually perfect conditions: zero clouds, a limiting magnitude of 6.5, and the radiant at the zenith.
		As the last of these never occurs in practice, and would be instantaneous in any event, the ZHR is always higher than the observed rate of meteors, typically by a factor of two or more depending on other restrictions such as moonlight, clouds and/or haze, and light pollution.
	members.shaw.ca /weskyscan/glossary.htm (3268 words)

	Observing Prospects For The Leonids
		Observed meteor rates on November 13-14, 1866 were in the order of 2000 to 5000 per hour, perhaps not as spectacular as in 1833.
		Observers noted a maximum hourly rate of 40 on November 14, but nothing that compared to what astronomers, and indeed the public, were expecting.
		The Hawaiian observers saw the hourly rates for the Leonids increase from 20 to around 120 within the space of 2 hours on 16th November and as Australia turned towards the radiant, 38 Leonids were reported with an average brightness of magnitude -3!
	gchbryant.tripod.com /Articles/Leonid1198.htm (3912 words)

	Zenith number - Encyclopedia Glossary Meaning Explanation Zenith number (Site not responding. Last check: 2007-09-05)
		A Zenith number was a special type of telephone number in the United States which a subscriber could obtain, which was introduced prior to the development of toll-free service, which allowed a calling party to dial the number's owner at no charge by dialing Operator and requesting the specified Zenith number.
		Some organizations continue to keep their Zenith numbers (The California Highway Patrol continues to use the same single number it has for decades, Zenith 1-2000), but with the low cost of incoming WATS service, the use of Zenith numbers has been deprecated to historical status.
		The reason the name Zenith was used is that the letter Z did not, at that time, appar on the telephone keypad, thus the only way one could dial a 'Zenith' number was to dial Operator.
	www.encyclopedia-glossary.com /en/Zenith-number.html (216 words)

	Chapter 8 (Site not responding. Last check: 2007-09-05)
		The zenithal hourly rate is a means by which different observers can convey their results to each other.
		Variables to consider include clouds, limiting magnitudes, observing periods, the radiant's zenith distance, geographical latitude of the observer, and the observer's own perception.
		HR = observed hourly rate; r = population index; LM = your average limiting magnitude; and A = altitude of the shower's radiant above the horizon in degrees
	www.astro.lt /ldangus/astro/leonidai/zhr.htm (204 words)

	Implementation (Site not responding. Last check: 2007-09-05)
		As explained before in 3.1 (Meteoroid Stream Parameter), the Zenithal Hourly Rate (ZHR) is a main parameter for meteoroid stream flux calculations.
		It is a summation of the contributions from the 50 given meteoroid streams with a background reference value of 10, which is the same in all ZHR plots.
		Figure 12: Zenithal Hourly Rate summation for the 50 given meteoroid streams with normal activities for a whole year and a background reference value of 10
	space-env.esa.int /External/reports/torsten/diplomarbeit/Implementation.html (435 words)

	NAMN Guide: Chapter 7 - Population Index
		The raw data obtained from meteor counts may be used in such studies as hourly rate profiles, meteor colors or train percentage rates.
		But almost all investigations include a determination of the ZHR (zenithal hourly rate - number of shower meteors an observer would see in one hour if the radiant were in the zenith, the limiting magnitude was +6.5, and the sky was cloudless).
		The population index is the essential quantity to permit any further analysis, so it must be used in the ZHR calculation.
	www.namnmeteors.org /guidechap7.html (505 words)

	[No title] (Site not responding. Last check: 2007-09-05)
		Input “1” for penetration stream flux, “2” for stream flux depending on a given mass or “3” for the Zenithal Hourly Rate.
		Zenithal Hourly Rate (ZHR) The ZHR is calculated as explained in Annex 1.
		Output is the ZHR versus the solar longitude in [degrees].
	space-env.esa.int /External/reports/torsten/Final_Report_149_98_BIELER.doc (2451 words)

	27 June '04 Major News about Minor Objects
		Based on a preliminary analysis of early reports to the IMO, the zenithal hourly rate (ZHR) curve suggests that rates briefly surged to a ZHR of perhaps 50 on June 23rd, only slightly less than the maximum ZHR (80) of the well known Perseids in August.
		Zenithal hourly rate is the number of meteors a “standard” observer would see if he or she was observing with the radiant at zenith (directly above the observer) and a limiting magnitude of +6.5.
		From the diagram it can be seen that rates were well over that for several hours spanning 22-23 June, therefore classified as an "outburst" at an unusual high level for this stream, which also displayed this kind of behavior in 1916 and 1998.
	www.hohmanntransfer.com /mn/0406/27.htm (1908 words)

	.:: Vallis Alpes : Comets & Meteors ::.
		To the naked eye they appear like detached portions of the The strength of a meteor shower is measured by its zenithal hourly rate (ZHR), which is the number of meteors that an individual observer would see if the radiant were directly overhead in a dark sky.
		Since the radiant is seldom, if ever, at the zenith, the number of meteors actually seen per hour will be less than the theoretical ZHR.
		The ZHR is only a guide, and can vary considerably from year to year.
	www.apsylus.com /vallis-alpes/comets.html (1257 words)

	Dublin Night Sky Observer: Observing Meteors
		The Zenithal Hourly Rate typically reaches 80, although some years have been as low as 4 and as high as 200.
		The number of meteors that are expected to be seen during a shower is measured in terms of Zenithal Hourly Rate (ZHR).
		This is the number of meteors visible with the naked eye, under ideal conditions, with the Radiant of the shower at the zenith (i.e.
	indigo.ie /~gnugent/dnso/articles/meteors.htm (887 words)

	Zenithal Hourly Rate - Wikipedia, the free encyclopedia
		In astronomy, the Zenithal Hourly Rate (ZHR) of a meteor shower is the number of meteors an observer would see in one hour under a clear, dark sky (limiting apparent magnitude of 6.5) and if the radiant of the shower were in the zenith.
		The rate which can effectively been seen is always lower and decreases as the radiant is closer to the horizon.
		This page was last modified 21:00, 4 May 2005.
	en.wikipedia.org /wiki/Zenithal_Hourly_Rate (98 words)

	Shooting stars
		A zenithal hourly rate (ZHR) of 40 meteors per hour (m/h) was tentatively assigned to the shower at this time.
		A preliminary ZHR of 200-250 was ascribed to this period.
		The ZHR at maximum was estimated to be of the order of 500.
	www.islamanswers.net /science/stars.htm (1750 words)

	Zenith Minisport - Encyclopedia Glossary Meaning Explanation Zenith Minisport (Site not responding. Last check: 2007-09-05)
		Zenith Minisport - Encyclopedia Glossary Meaning Explanation Zenith Minisport.
		The Zenith MiniSport (circa 1989) was a small laptop based on a 80C88 CMOS CPU running at 4.77MHz or 8MHz, software.
		Called FastLynx, it relied on the user typing in a DOS Mode command on the other computer, which transferred control of that computer's command line to the Zenith over the serial line.
	www.encyclopedia-glossary.com /en/Zenith-Minisport.html (252 words)

	Meteor Glossary
		The length from the horizon to the point straight up in the sky (zenith) is 90 degrees.
		Zenithal Hourly Rate (or ZHR) - The rate of meteors that an observer under very dark skies would see if the radiant were overhead.
		The ZHR is almost always greater than the actual number of meteors a sky-watcher can see.
	www.spaceweather.com /meteoroutlook/meteorglossary.html (540 words)

	Leonid Predictions for 2001 - BIG meteor shower (Site not responding. Last check: 2007-09-05)
		They said the hourly rates would not be as high as in 1999, noting there was not enough information on the first peak to hazard a guess, but that rates of 100 per hour were possible during the two peaks on the 18th.
		Interestingly, Rao determined that rates of 250-500 per hour were possible on the 17th, while the peak at 7:51 UT could have rates ranging from 20 to 2800 per hour.
		As for the maximum rates at each peak, none of the models were consistently close, with the actual zenithal hourly rates coming out to 130 at 8:07 UT on November 17, 290 at 3:24 UT on November 18, and 480 at 7:12 UT on November 18.
	www.freerepublic.com /forum/a3bd65b7112e3.htm (4064 words)

	Leonid Meteor Storm Materializes Around Expected Peak Time
		Meteor astronomers reduce the actual numbers of meteors seen to a standard value, called the Zenithal Hourly Rate (ZHR), which takes into account the quality of the sky as well as the direction from which meteoroids enter the atmosphere.
		ZHR levels were above 1000 from roughly 1h30m UT to 3h00m UT corresponding to 235.26 to 235.32 degrees in solar longitude.
		ZHRs are computed with a population index of 2.0, zenithal exponent of 1.0.
	neo.jpl.nasa.gov /news/news079.html (604 words)

	Meteors 2
		The visual strength of a meteor shower is measured by its Zenithal Hourly Rate (ZHR), defined as the number of meteors a single average observer would see if the radiant were directly overhead and the sky dark and transparent with a limiting stellar magnitude of 6.5 (conditions that are rarely met in practice).
		The equivalent hourly rate (like ZHR) is measured for a sky with a limiting stellar magnitude of +6.5.
		Total meteor rates on a given night may be somewhat higher due to contributions from minor showers.
	www.skyscan.ca /meteors_2.htm (1126 words)

	Desert Storm - The 1999 Leonid Meteor Shower
		Painstaking observers maintained counts of meteors, observing the sky away from the direction of the radiant, which could then be converted to a Zenithal Hourly Rate to allow direct comparison with previous showers.
		Rates such as this had not been seen since the previous Leonid storm in 1966.
		However the peak of the storm was short lived, so a meteor rate measured in meteors per hour is misleading.
	www.britastro.org /sinai_leonids99/reports/frost.html (1139 words)

	Olle Eriksson's homepage
		ZHR (Zenithal Hourly Rate) is the value used by astronomers to define the number of meteors that can be spotted by the human eye in one hour if the radiant of the meteor shower is seen at zenith.
		Use it to calculate the ZHR of a meteor shower based on your own personal meteor observations.
		Remember that the ZHR value stands for the number of meteors seen during a whole hour.
	www.olle-eriksson.com /Default.aspx?page=Article&id=113 (560 words)

	Celestial Delights \| Leonids 2003: After the Storms
		Vaubaillon forecasts a peak Zenithal Hourly Rate, or ZHR, of 120 meteors during that period.
		The Zenithal Hourly Rate, or ZHR, is a highly idealized estimate and observers always see lower numbers of meteors than indicated by that value.
		Although Lyytinen admitted that there was " barely enough computed data" for a detailed analysis, he noted that the stream shows a maximum ZHR " of about 70." He also believes that the stream should be considered a part of the Filament.
	www.spaceweather.com /delights/ms/leonids2003.html (1716 words)

	SkyTonight.com - News from SkyTonight - An Average Perseid Meteor Shower
		Many skywatchers in the eastern United States, however, were disappointed by summer haze that dimmed the view of the stars and hid most of the meteors.
		This suggests that the shower's actual "zenithal hourly rate" at the time was around 80, its textbook average.
		The zenithal hourly rate (ZHR) is the number of meteors a single observer would see if the sky were dark enough for 6.5-magnitude stars to be visible, and if the shower's radiant (in northern Perseus) were at the zenith.
	skytonight.com /news/3306476.html?page=1&c=y (327 words)

	Space and Beyond
		Although the peak of activity is predicted to occur on May 4, it pays to watch a few days either side of this date: In 1997 the peak occurred a day early.
		The peak is broad, giving almost a week a good activity above a zenithal hourly rate (the rate calculated for perfect observing conditions if the radiant were to lie directly overhead) of 30 meteors per hour.
		The sudden and brief improvement in reception of a normally difficult-to-receive radio station indicates the passage of a meteor often run significantly higher than visual rates, and Eta Aquarids are good shower to check this out.
	library.thinkquest.org /C004639/calendar/may.htm (458 words)

	Lab Write-Up (Site not responding. Last check: 2007-09-05)
		Convert your count of the number of meteors to a zenithal hourly rate.
		The 6° is an 0 correction for haze near the horizon.
		Divide the observed rate by the sine to find the zenithal hourly rate.
	www.astro.virginia.edu /~teacha/130_manual/node86.html (293 words)

	Leonids 2000
		This unusually spiky ZHR profile threw more than one observer into confusion as there wasn't the steady rise over several hours towards the peaks - when the radiant rose at the geometrically optimal sites in Europe and America, the rates were surprisingly low, only to take off after several hours.
		The ZHR refers to a stellar limiting magnitude of +6.5, a radiant elevation of 90 deg, and counts of single observers.
		In the period 4:15am to 4:30am the rate was initially high but fell of markedly in the last 3 or 4 minutes, 91 spotted in that 15 minute period.
	www.xs4all.nl /~carlkop/leo2002e.html (5815 words)

	2003 Meteor Showers
		Many streams have a complex rate profile; for example, the Eta Aquarid and Orionid showers have earlier peaks for faint meteors than for bright meteors.
		Some showers (such as the Leonids) have meteoroids concentrated in a small region of the orbit and hence have much higher peak rates in certain years.
		For example, for a limiting magnitude of +3.5, a shower with a ZHR of 60 and a population index r = 2.8 would have the number of observable meteors per hour reduced by a factor of (2.8)3 to a rate of only 2.7 meteors per hour.
	www.skyscan.ca /2003_meteor_showers.htm (660 words)

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