{"id":29045,"date":"2022-02-10T00:00:00","date_gmt":"2022-02-10T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=29045"},"modified":"2022-03-23T13:17:57","modified_gmt":"2022-03-23T13:17:57","slug":"the-sky-guide-challenge-6","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2022\/02\/10\/the-sky-guide-challenge-6\/","title":{"rendered":"The sky guide challenge"},"content":{"rendered":"\n

Can you spot the Moon\u2019s eastern libration features this month?<\/p>\n\n

\"\"
This month is a good opportunity to see the Moon\u2019s eastern limb libration features, which become visible as a result of the Moon\u2019s rocking motion; these include three seas, Mare Humboldtianum, Mare Marginis and Mare Smythii, and the 207km crater Humboldt (inset)<\/figcaption><\/figure><\/div>\n\n

The Moon is tidally locked to Earth, rotating once on its axis in the same time it takes to complete each orbit. From Earth this means we get to see the same familiar features revealed and hidden as the Moon passes through its phase cycle. Looking at the Moon at higher magnification reveals that there is slight variation in this view. This month\u2019s challenge is to take advantage of this effect to spot some tricky edge features.<\/p>\n\n

The variation is mostly caused by the Moon\u2019s elliptical and tilted orbit. The ellipticity causes a variation in the Moon\u2019s orbital speed which allows us to see slightly further round the eastern or western side of the Moon\u2019s globe. The tilt causes the Moon to bob up and down relative to the plane of Earth\u2019s orbit (the ecliptic plane). The tilt isn\u2019t much at around 5\u00b0, but it does allow us to see further round the Moon\u2019s southern and northern edges.<\/span><\/p>\n\n

The variations are collectively known as lunar libration and over time 59 per cent of the Moon\u2019s globe can be seen. Actually, seeing 59 per cent of the Moon\u2019s globe is easier said than done as in order to see a specific edge feature, the libration has to be favourable as does the lunar phase. In addition, the Moon has to be above your horizon and, of course, the weather has to play ball.<\/p>\n\n

This month there is a good opportunity to spot eastern libration features; lunar features which can only be seen under favourable libration. The very thin, 2%-lit waxing crescent Moon on the evening of 3 March shows the three eastern seas, Mare Humboldtianum, Mare Marginis and Mare Smythii. The magnificent 207km crater Humboldt is also well positioned on this date. This Moon sets 70 minutes after the Sun, so isn\u2019t an easy target.<\/span><\/p>\n\n

On the evenings of the 4th and 5th, the Moon appears at a greater phase and stays up progressively longer after sunset. Libration remains favourable for the features mentioned, but starts to become less optimal after the 6th.<\/p>\n\n

One aspect which does work in our favour during March is the position of the waxing Moon in the early evening sky. The ecliptic makes a steep angle with the western horizon around sunset at this time of year. Despite its orbital tilt of 5\u00b0 from the ecliptic plane, the Moon tends to stay close to the ecliptic in the sky, and consequently, it\u2019s approach vector towards the western horizon in March also appears steep. This gives it a good altitude post sunset which is ideal for us when we want to observe or image it.<\/p>\n\n

Photo: PETE LAWRENCE<\/p>\n","protected":false},"excerpt":{"rendered":"

Can you spot the Moon\u2019s eastern libration features this month?<\/p>\n","protected":false},"author":24,"featured_media":29044,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"55","purple_custom_meta_purple_page_number":"55","purple_seq_number":"1","purple_custom_meta_purple_seq_number":"1","purple_source_article":"article_55-1.xml","purple_custom_meta_purple_source_article":"article_55-1.xml","purple_source_issue":"March-2022","purple_custom_meta_purple_source_issue":"March-2022","purple_external_id":"March-2022-55-1","purple_custom_meta_purple_external_id":"March-2022-55-1","purple_issue_code":"|0000086550||","purple_custom_meta_purple_issue_code":"|0000086550||","purple_android_product":"com.im.skyatnight.202","purple_custom_meta_purple_android_product":"com.im.skyatnight.202","purple_ios_product":"com.im.skyatnight.202","purple_custom_meta_purple_ios_product":"com.im.skyatnight.202","purple_web_product":"","purple_custom_meta_purple_web_product":"","purple_publication_id":"075fab74-0a21-4201-866a-899d6c41c40c","purple_migrated":"","kt_blocks_editor_width":""},"categories":[22],"tags":[14],"featured_image_src":"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"3","apple_news_title":""},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2.jpg",2048,1373,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2-300x201.jpg",300,201,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2-768x515.jpg",768,515,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2-1024x687.jpg",800,537,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2-1536x1030.jpg",1536,1030,true],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/02\/1646e76e-cbb9-4e50-9b6c-ec1168c05da2.jpg",2048,1373,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"Can you spot the Moon\u2019s eastern libration features this month?","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/29045"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"replies":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/comments?post=29045"}],"version-history":[{"count":3,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/29045\/revisions"}],"predecessor-version":[{"id":29517,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/29045\/revisions\/29517"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/29044"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=29045"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=29045"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/tags?post=29045"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}