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Meteor Shower Radiant Calculator

Calculate geometric radiant altitude and azimuth from declination, observer latitude and local hour angle. Supports degrees or sidereal hours.

Use this result well

Inputs that matter
Radiant declination (°), Observer latitude (°), Local hour angle unit, Local hour angle
Output to expect
Meteor Radiant Altitude and Azimuth
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Coordinate transformation

Resolve the entered direction into east, north and up components. The two-argument arctangent preserves the azimuth quadrant. Angles are converted to radians internally.

Source: US Naval Observatory — Altitude and Azimuth

Conventions and singularities

Local hour angle increases westward, with 15 degrees per sidereal hour. Full turns wrap. Azimuth runs clockwise from true north and is undefined at zenith, nadir and geographic poles.

Limits

The result is geometric: atmospheric refraction, local obstructions and observing conditions are not modeled. Six-decimal display precision does not imply equivalent accuracy in the input coordinates.

Updated: September 2026

Example Scenarios

Compare an entered declination with the observer latitude at hour angle zero.

Use negative and positive local hour angles with the same declination and latitude.

Common Mistakes to Avoid

Entering clock time as hour angle

Use local sidereal time minus right ascension in compatible units. Clock time alone is insufficient.

Interpreting altitude as a forecast

Check darkness, weather, Moon, obstructions and actual shower activity separately.

FAQ

No. Supply the radiant declination and local hour angle yourself; the tool has no event calendar.

At zenith or nadir the direction has no horizontal bearing. At a geographic pole the ordinary local north reference is not unique.

They represent the same direction. Complete rotations are removed before calculation.

No. It describes the entered instant geometrically and does not include refraction, terrain or a time search.

About Meteor Shower Radiant Calculator

Enter known radiant coordinates for your observing time. This tool transforms angles; it does not find a shower peak, fetch a radiant catalog or predict how many meteors you will see.