From Wikipedia, the free encyclopedia Zenithal Hourly Rate
Zenithal Hourly Rate
k is the percentage of the observer’s field of view which
is obstructed (by clouds, for example).
Example: If 20% of the observer’s field of view were cov-
ered by clouds, k would be 0.2 and F would be 1.25. The
observer should have seen 25% more meteors, therefore
we multiply by F = 1.25.
r6.5 − lm
This represents the limiting magnitude correction
factor. For every change of 1 magnitude in the limiting
magnitude of the observer, the number of meteors ob-
The 2010 Perseids over the VLT served changes by a factor of r. Therefore we must take
this into account.
ZHR)
In astronomy, the Zenithal Hourly Rate (ZHR of a
meteor shower is the number of meteors a single observ- Example: If r is 2, and the observer’s limiting magnitude
er would see in one hour under a clear, dark sky (limiting is 5.5, we will have to multiply their hourly rate by 2 (2
apparent magnitude of 6.5) if the radiant of the shower to the power 6.5-5.5), to know how many meteors they
were at the zenith. The rate that can effectively be seen is would have seen if their limiting magnitude was 6.5.
nearly always lower and decreases the closer the radiant
is to the horizon. sin(hR)
This represents the correction factor for altitude of
The formula to calculate the ZHR is: the radiant above the horizon (hR). The number of mete-
ors seen by an observer changes as the sine of the radiant
height in radians.
Example: If the radiant was at an average altitude of 30°
during the observation period, we will have to divide the
where
observer’s hourly rate by 0.5 (sin 30°) to know how many
meteors they would have seen if the radiant was at the
zenith.
represents the hourly rate of the observer. N is the
number of meteors observed, and Teff is the effective ob- See also
servation time of the observer. • List of meteor showers
Example: If the observer detected 12 meteors in 15 min-
utes, their hourly rate was 48. (12 divided by 0.25 hours). External links
• North American Meteor Network (NAMN)
This represents the field of view correction factor, where
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Categories:
• Meteoroids
• Observational astronomy
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From Wikipedia, the free encyclopedia Zenithal Hourly Rate
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