Meteor Shower Observed Rate Calculator
The meteor counts in the headlines are measured in a perfect sky with the shower directly overhead, so almost nobody sees them. Tell this page which shower, which night and where you are standing, and it works out the number you should really expect, hour by hour. Nothing uploaded.
What each correction costs you
Read top to bottom: every line multiplies the one above it. The published rate is the starting point, not the answer.
Hour by hour through the night
The moon that night
What a darker sky would buy you
Same shower, same hour, same horizon. Only the sky brightness changes. Unsure which line is yours? The light pollution calculator gets you there by counting stars in the Little Dipper.
Take it outside
Copies the plan as plain text, assumptions included, so the numbers travel with the reasoning behind them.
Learn more: why a shower never delivers its headline number
What the ZHR actually promises
A shower's zenithal hourly rate is not a forecast of what anyone will see. It is a normalised figure, built so that counts made on different nights, from different places, by different observers can be compared against each other at all.
The International Meteor Organization's calendar defines it as "a calculated maximum number of meteors an ideal observer would see in perfectly clear skies (reference limiting magnitude +6.5) with the shower radiant overhead". Every word of that is a condition you are unlikely to meet.
Observers report their raw counts, and analysts scale those counts up to the reference conditions to get a ZHR. This calculator runs the same relation backwards, scaling the published figure back down to your actual sky.
The three corrections, and which one hurts most
The standard visual relation, as the Wikipedia article on the zenithal hourly rate sets it out, is ZHR = HR × F × r^(6.5 - lm) ÷ sin(h). Rearranged for the rate you see, that is HR = ZHR × sin(h) × r^(lm - 6.5) × (1 - k).
The radiant altitude term is the gentlest of the three. With the radiant 30 degrees up you keep half the rate, at 45 degrees you keep 71%, and only directly overhead do you keep all of it.
The sky brightness term is the brutal one, because it is exponential rather than proportional. Each magnitude of sky glow divides your rate by the shower's population index r, so a two-magnitude loss at r = 2.5 divides it by more than six.
Obstruction is the one that behaves the way people expect. Block a third of the sky with a hedge and you lose a third of the meteors, since they arrive from every direction rather than only from the radiant.
Worked through for the Perseids at r = 2.2 and a ZHR of 100, with the radiant at 30 degrees, a limiting magnitude of 4.5 and nothing in the way: 100 × 0.5 × 2.2^(-2) = 10 meteors an hour. The same night from a dark site at magnitude 6.5 with the radiant at 60 degrees gives 87. Same shower, same peak, more than eight times the meteors.
Where the shower figures come from
The ZHR, population index and radiant position for each shower in the list are the IMO's Working List of Visual Meteor Showers, as published in the 2025 edition of the calendar linked above. The Perseids are listed at ZHR 100 with r = 2.2, the Geminids at 150 with r = 2.6, and the Quadrantids at 80 with r = 2.1.
Those population indices matter more than they look. The Quadrantids at 2.1 and the Sigma Hydrids at 3.0 lose very different amounts to the same streetlight: two magnitudes of sky glow costs the first shower 77% of its meteors and the second 89%.
Where the list gives a single radiant position, it is the position at the shower's maximum. Radiants drift by a degree or so a day, which is far too small to change the answer here.
The advanced panel takes your own ZHR, r and radiant if you are chasing a predicted outburst or a shower the list does not carry.
How the sky positions are worked out
The radiant altitude comes from the standard hour-angle formula, sin(altitude) = sin(declination)sin(latitude) + cos(declination)cos(latitude)cos(hour angle), with the hour angle taken from local sidereal time at your longitude.
The sun and moon positions use the low-precision series from Paul Schlyter's planetary position tutorial, which gives the moon to a couple of arcminutes. That is far finer than a rate calculation needs, where a whole degree of radiant altitude near 45 degrees moves the answer by under 2%.
An hour counts as dark here when the sun is more than 12 degrees below the horizon, which is the end of nautical twilight. The last of the glow does not clear until 18 degrees, but the difference between the two costs a meteor count far less than the radiant altitude you would give up by waiting.
The earlier hours are still listed, marked as twilight, because that is exactly where an evening radiant like the Draconids does its best work.
Why the moon is reported rather than modelled
Moonlight raises the background brightness of the whole sky, which lowers your limiting magnitude, which feeds straight into the exponential term. That much is not in doubt.
How much it lowers it is another matter. It depends on the moon's altitude and phase, how far from the moon you are looking, the haze in the air and your own eyes, and no single number covers it honestly.
So the page computes the moon's altitude and illuminated fraction for every hour and tells you plainly when it is in the way, but the allowance in magnitudes is yours to set in the advanced panel. Set it from your own experience of your own site, or take the reliable route and measure your limiting magnitude on the night, with the moon up, by counting the stars you can see.
Reading a small number honestly
At 12 meteors an hour you are not seeing one every five minutes. Meteors arrive at random, so the gaps clump: a quarter of an hour of nothing, then three in a minute.
This is the part that ruins people's nights more often than the arithmetic does. A rate of 12 an hour is a genuinely good session, and it will still contain long stretches where nothing happens at all.
The whole-night total is the more useful planning number for that reason. It sums the expected rate across every dark hour, so two hours out at 20 an hour beats five minutes of peering out of a window during a shower billed at 150.
FAQ
Why do I never see the number of meteors the news quotes?
Because that number is the ZHR, which is defined for a sky nobody has: the radiant straight overhead, stars visible down to magnitude 6.5, and nothing blocking the view. Three corrections stand between it and you. The radiant sits at some altitude below the zenith, so you keep the sine of that altitude. Your sky is brighter than magnitude 6.5, so you keep r raised to the power of your limiting magnitude minus 6.5. Trees, buildings or cloud take their share on top. A Perseid peak billed at 100 comes out near 10 an hour from a suburban garden at magnitude 4.5 with the radiant at 30 degrees.
Is it worth driving somewhere darker to watch a meteor shower?
For meteors the darkness correction is usually the biggest single lever you control, and it is steeper than people expect because it compounds. Going from a limiting magnitude of 4.5 to 6.0 during the Geminids, whose population index is 2.6, multiplies your rate by 2.6 to the power of 1.5, which is about 4.2 times as many meteors. The radiant altitude is fixed by the clock and your latitude, and the moon is fixed by the calendar, so the drive is the one factor still in your hands on the night.
What time of night should I actually go outside?
Whenever the radiant is highest and the sky is still properly dark, which for most northern showers means the hours before dawn rather than the evening. The rate tracks the sine of the radiant altitude, so it roughly doubles going from 15 degrees up to 30, and doubles again by 90. The hour-by-hour table here does that arithmetic for your own latitude and longitude, including where morning twilight cuts the night short.