Talk:Zenithal hourly rate

sin(hR) dependence[edit]

In the photograph of the Leonid shower in this page, the radiant seems to be ~30° above the "left" horizon and the meteors seem to travel all the way to the opposite horizon, i.e. over about 150°. However, as soon as the radiant is on the horizon, the meteor rate goes to zero, according to the sin(hR) term, whereas the fact that these meteors can travel at least 150° suggests they should easily make it beyond the zenith and plenty should be visible. Naively, I would expect to be able to see some meteors even if the radiant is (not too far) below the horizon. Could the sin(hR) term be too dramatic? AstroFloyd (talk) 08:33, 11 May 2014 (UTC)[reply]

I was just about to comment on the exact same thing. It seems total rubbish to assume that the radiant is on the horizon, with someone at sea level, no meteors will be seen. Drkirkby (talk) 09:31, 13 August 2018 (UTC)[reply]

I'm not going to edit it, as I don't know what the problem is. It could be the definition of Zenithal hourly rate is fundamentally flawed, or it could be someone has written the equation incorrectly. Whether the equation is written correctly, but the definition is flawed definition, or whether the equation is correct, but mistyped into Wikipedia I have no idea. But the article has serious issues. I have marked as dubious, as I am no expert on this. I'm just applying the most basic of schoolboy maths/science. Drkirkby (talk) 09:39, 13 August 2018 (UTC)[reply]

The ZHR equation does not imply that if the radiant is on the horizon, that no meteors will be seen. On the contrary, the sin(hR) simply provides a correction factor that converts the observed hourly rate into the equivalent zenithal hourly rate. For example, if the radiant is directly overhead, then sin(90) = 1, and no correction is needed. If the radiant has an elevation of 30 degrees, then sin(30) = 0.5, which means that the observed meteor count has to multiplied by 1/0.5 = 2 to get the equivalent zenithal hourly rate. If the radiant is on the horizon, then sin(hR) = 0, which means that the observed meteor count has to be multiplied by 1/0 = infinity to get the equivalent zenithal hourly rate. This may seem like an extreme correction (it is!), but meteors are quite rare when the radiant is at such a low altitude.

When the radiant is on the horizon, we may occasionally have earth-grazing meteors that skim along the top of the atmosphere, producing very long trails. When the radiant is below the horizon, then earth's curvature ensures that any meteors coming from the radiant will not be able to intersect earth's atmosphere at a point above the observer.

Postscript. Chapter 7 of the IMO Meteor Observation Handbook explains that the 1/sin(hR) correction factor works well when radiant elevation > 10 degrees. When the radiant elevation is lower, the correction factor becomes "more complicated." The handbook explains that meteors can still be seen if the radiant is slightly below the horizon.

REFERENCE: https://www.imo.net/imo-meteor-observation-handbook/

Bottom Line is that the sin(hR) factor in the denominator of the equation for ZHR is quite reasonable when hR > 10 degrees. Perhaps this qualification should be added to the article. — Preceding unsigned comment added by 24.170.205.55 (talk) 22:43, 28 December 2019 (UTC)[reply]

Magnitude correction factor[edit]

The magnitude correction factor $r^{6.5-lm}$ needs to be applied in the equation for the ZHR. The text explains what lm is, but not what r is, which makes the correction unusable and the ZHR equation (and much of this page — if I may play the devil's advocate for a moment) pointless. — Preceding unsigned comment added by AstroFloyd (talk • contribs) 08:42, 11 May 2014 (UTC)[reply]

Who advanced this as a theory and why?[edit]

I’m looking it up but am not an expert 173.73.130.14 (talk) 17:09, 31 May 2022 (UTC)[reply]

Citations[edit]

I noticed that this had gone with citations for 11 years and thought that was pretty crazy so I found some. I still think some additional citation is needed, especially for the calculation section. I found this paper here which is also where I found the citation for the magnitude needing to be 6.5 as a minimum. The paper "presents a mathematical model to simulate the trajectory of a meteor as seen by a single observer located anywhere on Earth." and includes a section for modeling the zenithal hourly rate.

Knaughty1234 (talk) 04:10, 13 September 2023 (UTC)[reply]