--- title: A Blue Moon Is Coming This Friday description: They happen about…once in a blue moon canonical: https://time.com/3976587/blue-moon/ author: Nolan Feeney article:opinion: false article:content_tier: free article:published_time: 2015-07-29T14:12:22.000Z article:modified_time: 2026-08-04T08:05:02.732Z article:section: Science og:title: A Blue Moon Is Coming This Friday og:description: They happen about…once in a blue moon og:url: https://time.com/3976587/blue-moon/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltde093bcdab65f2d0/6988d9b9bc6cfc69913e2a3c/time-logo.jpg?branch=production og:image:width: 1200 og:image:height: 675 og:image:alt: TIME og:type: article twitter:card: summary_large_image twitter:title: A Blue Moon Is Coming This Friday twitter:description: They happen about…once in a blue moon twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltde093bcdab65f2d0/6988d9b9bc6cfc69913e2a3c/time-logo.jpg?branch=production --- # A Blue Moon Is Coming This Friday ## Video: A Year in Space - Ep.1: Leaving Home [Watch (HLS stream): A Year in Space - Ep.1: Leaving Home](https://cdn.jwplayer.com/manifests/6ookw4W2.m3u8) (13:31)  _Published 2021-03-11. A Year in Space - Ep.1: Leaving Home_  by [Nolan Feeney](https://time.com/author/nolan-feeney/)  ## Nolan Feeney Jul 29, 2015 2:12 PM UTC  by [Nolan Feeney](https://time.com/author/nolan-feeney/)  ## Nolan Feeney Jul 29, 2015 2:12 PM UTC Blue moons aren’t actually blue, but they are as rare as the saying goes. The second full moon in a month is commonly referred to as a blue moon—we had a full moon on July 2, and we’ll have another this Friday on July 31—but there’s [a more complicated definition](http://www.usno.navy.mil/USNO/tours-events/sky-this-week/the-sky-this-week-2013-august-20-27) according to the U.S. Naval Observatory: --- > “” --- ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/3976587/blue-moon/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/3976587/blue-moon/"},"headline":"A Blue Moon Is Coming This Friday","datePublished":"2015-07-29T14:12:22.000Z","dateModified":"2026-08-04T08:05:02.732Z","description":"They happen about…once in a blue moon","url":"https://time.com/3976587/blue-moon/","keywords":["astronomy","weather"],"thumbnailUrl":"","author":[{"@type":"Person","name":"Nolan Feeney","jobTitle":null,"url":"https://time.com/author/nolan-feeney/"}],"articleSection":"Science","image":[],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/science/","name":"Science"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/astronomy/","name":"astronomy"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/3976587/blue-moon/","name":"A Blue Moon Is Coming This Friday"}}]},{"@context":"https://schema.org","@type":"VideoObject","name":"A Year in Space - Ep.1: Leaving Home","description":"A Year in Space - Ep.1: Leaving Home","thumbnailUrl":"https://cdn.jwplayer.com/v2/media/6ookw4W2/poster.jpg?width=720","uploadDate":"2021-03-11T18:13:57.000Z","contentUrl":"https://cdn.jwplayer.com/manifests/6ookw4W2.m3u8","embedUrl":"https://time.com/3976587/blue-moon/","duration":"PT13M31S","potentialAction":{"@type":"SeekToAction","target":"https://time.com/3976587/blue-moon/?jw_start={seek_to_second_number}","startOffset-input":"required name=seek_to_second_number"}}] ```