Zenithal Hourly Rate

The Zenithal Hourly Rate ( ZHR , German about zenitale hourly rate ) of a meteor shower is the number of meteors that an observer sees within one hour under a sky with the visual limit size 6.5 ^m , if the radian of the current is exactly in the zenith and there is no obstacle in the field of view.

Since this ideal situation cannot occur exactly, the true observed rate is always lower than the theoretical Zenithal Hourly Rate : ${\displaystyle {\tfrac {N}{t}}}$

${\displaystyle ZHR>{\frac {N}{t}}}$

With

• N: number of meteors observed
• t: observation time in hours.

Using the following formula, the observed rate can be approximately converted into the Zenithal Hourly Rate :

${\displaystyle ZHR\approx {\frac {N}{t}}\cdot {\frac {r^{6,5-m_{gr}}}{\sin h}}}$

With

• r (> 1): population index , i.e. H. Brightness distribution of the observed meteor shower
• ${\displaystyle m_{gr}}$: Limit size of the faintest stars observable with the naked eye in the current observation
• h: Angle of elevation of the radian of the observed meteor shower above the horizon , measured at the middle of the observation period.

Since the current limit value will often be below the very good 6.5  magnitudes that apply to the ZHR itself, the above results. Formula an exponent  > 0 for the population index r. ${\displaystyle m_{gr}}$

Web links

Wiktionary: Zenithal Hourly Rate  - explanations of meanings, word origins, synonyms, translations

• NAMN: The Zenithal Hourly Rate