Saturday, November 28, 2009
ZHR is not the same as HR
When the predicted rate is announced as 500 ( or later scaled down to 200), the public including the media take it as Hourly Rate 500 or 200 perhaps ignoring the 'Zenith' term of Zenith Hour Rate.
A simple worksheet above illustrate the poor LM sky to Predicted ZHR vs Hourly Rate ( HR) . Unless the LM is 6.6 which means 2^(6.5-6.5)=2^0=1 and radiant is directly overhead Sine(90)=1 you will never get the hour rate = ZHR. With our less than ideal LM - the worksheet says ~ 14 Leonids /HR can be seen during the peak. Recompute the above with a good dark site where LM is 6.3. Now you can see the HR is 147 (200Zhr pred), and (500Zhr pred).
So the message is GO for a DARK SITE with good sky to appreciate the high hourly rate. Please also take note that while the shower members dominate during peak not all meteors seen were from Leonids - there are other active meteor streams and background sporadic too.
For coming Geminids ( high radiant around midnite) - if you keep the radiant within edges of your field of view you can check by extrapolation backward path of the meteor.. if it falls within the radiant area then high chance it is a Geminid (Gem) .....