29:null 2a:["$","title",null,{"children":"Julian Date (JD) calculator | Christophe Yamahata | Observable"}] 2f:[] 2d:{"id":"79295788ee92b55b","slug":"julian-date-calculator","title":"Julian Date (JD) calculator","thumbnail":"4372071c1d9be90d43909ba6ba6f6dccc5f3912da7cd241318ba2544d733b759","access_level":"public","create_time":"$D2024-05-19T18:24:42.388Z","update_time":"$D2024-05-20T00:12:43.648Z","view_time":null,"first_public_time":"$D2024-05-19T20:45:19.683Z","has_unpublished_edits":null,"fork":false,"stars":0,"starred":false,"owner":{"type":"team","id":"dd67891d326bcfb1","login":"christophe-yamahata","name":"Christophe Yamahata","avatar_url":"https://avatars-next.observableusercontent.com/8256ac716aa8395babba412b2835913d186874fa4190df57a4a28f2e60129876","tier":"starter_2024"},"version":264,"publish_version":null,"role":null,"authored":false,"authors":[{"type":"individual","id":"06f083eba60f5a76","login":"christophe-yamahata","name":"Christophe Yamahata","avatar_url":"https://avatars-next.observableusercontent.com/8256ac716aa8395babba412b2835913d186874fa4190df57a4a28f2e60129876","tier":null}],"members":[{"type":"individual","id":"06f083eba60f5a76","login":"christophe-yamahata","name":"Christophe Yamahata","avatar_url":"https://avatars-next.observableusercontent.com/8256ac716aa8395babba412b2835913d186874fa4190df57a4a28f2e60129876","tier":null,"role":"editor"},{"type":"team","id":"dd67891d326bcfb1","login":"christophe-yamahata","name":"Christophe Yamahata","avatar_url":"https://avatars-next.observableusercontent.com/8256ac716aa8395babba412b2835913d186874fa4190df57a4a28f2e60129876","tier":"starter_2024","role":"viewer"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":0,"collection":{"id":"a4317cf9df48c2f1","slug":"sandbox","title":"Sandbox","owner":{"id":"dd67891d326bcfb1","login":"christophe-yamahata","name":"Christophe Yamahata"}},"type":"notebook","body":{"title":"Julian Date (JD) calculator","cells":[{"id":0,"value":"# Julian Date (JD) calculator","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":28,"value":"

The Julian Date is particularly useful in astronomy and other scientific fields as it provides a continuous count of days since a starting epoch, allowing for precise timekeeping and easy calculation of time intervals between events across different calendar systems.

This notebook provides a straightforward means for calculating the Julian Date (JD).\nTo proceed, manually enter a date or select it from the calendar.

","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":5,"value":"viewof date = Inputs.date({label: htl.html`Input date:`, required: true, min: \"0100-01-01\", max: \"9999-12-31\"})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":52,"value":"
\n

Result

\nThe date selected is (YYYY-MM-DD): \n
${format(date)}\n
The corresponding Unix timestamp (UT) for this date at midnight is:\n
UT = ${fformat(UT(date))} seconds (counted from midnight UTC on January 1, 1970 )\n
The corresponding Julian date (JD), calculated at noon, is: \n
JD = ${fformat(JD(UT(date)))} days","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":170,"value":"
\n

Notes

\n This notebooks makes use of the Unix time. The reason for passing through the Unix timestamp is that this function is implemented in JavaScript. \n This approach ensures an accurate and easy calculation of the Julian Date using a widely understood reference point.\n The calculation is therefore straightforward:\n

${tex`JD = \\frac{UT}{86400} + 2\\,440\\,587.5`} \n

with ${tex`JD`}, the Julian Date expressed in days,\n
and ${tex`UT`}, the Unix timestamp expressed in seconds.\n

The Unix time 0 is exactly midnight UTC on January 1, 1970.
The \".5\" value indicates that JD is calculated for noon (i.e., half-day).

","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":207,"value":"

Example

","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":211,"value":"viewof date_now = Inputs.date({label: htl.html`Current date:`, value: Date.now(), disabled: true})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":217,"value":"Julian date for current date: \n
JD (${format(date_now)}) = ${fformat(JD(Date.parse(date_now)/1000))} days","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":98,"value":"

","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":81,"value":"### Appendix","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":78,"value":"date","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":7,"value":"UT = date => Date.parse(date)/1000;","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":9,"value":"JD = UT => Math.round(UT / 86400,0) + 2440587.5\n","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":62,"value":"format = d3.timeFormat(\"%Y-%m-%d\")","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":233,"value":"locale = d3.formatLocale({\n decimal: \".\",\n thousands: \"\\u00a0\",\n grouping: [3],\n})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":236,"value":"fformat = locale.format(\"$,\")","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W2f","stdlib":"1","titling":"auto"}} 2e:"$2d:body"