Moon illumination and phase at a datetime, or daily over a date range.

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Overview

Returns the fraction of the Moon's disc that is illuminated at a given location and datetime. The response includes the raw fraction (0.0 to 1.0), the percentage (0 to 100), and a formatted string. Computed using Skyfield's fraction_illuminated method, which calculates the angle between the Sun and Moon as seen from Earth. A value of 1.0 (100%) corresponds to a full Moon; 0.0 corresponds to a new Moon. Use this alongside astra/moon/phase/ to get both the numeric illumination and the named phase.

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Request parameters

Name	Type	In	Required	Description	Example
date1	Date	Body	Yes	The start date (or single query date) for the computation. Accepted formats: YYYY-MM-DD for date-only fields, ISO 8601 datetime string (YYYY-MM-DDTHH:MM) for datetime fields.
lat	Float	Body	Yes	Observer latitude in decimal degrees. Valid range: -90.0 (South Pole) to 90.0 (North Pole). Used to compute the observer's position on Earth's surface for all sky calculations.
lon	Float	Body	Yes	Observer longitude in decimal degrees. Valid range: -180.0 to 180.0. Negative values are west of the Prime Meridian, positive values are east.
date2	Date	Body	Optional	The end date of the query range. Must be on or after date1. Accepted format: YYYY-MM-DD. The range is inclusive of both dates.
timezone_slug	Choice	Body	Optional	Slug of a timezone record used to localise event datetimes in the response (e.g. america-new-york). When omitted, the timezone is derived automatically from the supplied coordinates. Obtain valid timezone slugs from the timezone list endpoint.

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Response fields

Name	Type	Nullable	Description	Example
date1	Datetime	—	Observation datetime echoed from the request.	2025-06-21T22:00:00
formatted_illumination	String	—	Illumination as a formatted percentage string.	87.3%
illumination	Float	—	Fraction of the Moon's disc that is illuminated, from 0.0 (new moon) to 1.0 (full moon).	0.873
illumination_percentage	Float	—	Illumination expressed as a percentage (0.0–100.0), rounded to one decimal place.	87.3
lat	Float	—	Observer latitude echoed from the request.	48.428333
lon	Float	—	Observer longitude echoed from the request.	-123.364722
tz	String	—	Resolved IANA timezone name.	America/Vancouver