{"id":64499,"date":"2024-10-08T10:05:35","date_gmt":"2024-10-08T10:05:35","guid":{"rendered":"http:\/\/16e8e277-a2d1-402b-8f0f-b4f7fe40a81d"},"modified":"2024-10-08T10:40:53","modified_gmt":"2024-10-08T10:40:53","slug":"rasalhague-brightest-star-in-ophiuchus","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/rasalhague-brightest-star-in-ophiuchus\/","title":{"rendered":"Rasalhague, brightest star in Ophiuchus"},"content":{"rendered":"

<\/p>

By Pete Lawrence\n <\/p>

Published: Tuesday, 08 October 2024 at 10:05 AM<\/p>

\n\n

At the top of Ophiuchus<\/a>, the Serpent Bearer, representing his head, is the star Rasalhague (Alpha (\u03b1) Ophiuchi).<\/p>

Close by is Rasalgethi, the head of another giant in the stars, located in the constellation Hercules<\/a>, the Strong Man.<\/p>

Rasalhague is a binary star<\/a> system, 48 lightyears from Earth. It has a faint companion, too close to its primary for amateur instruments to see.<\/p>

Chart showing the location of star Rasalhague in the constellation Ophiuchus. Click to expand. Credit: Pete Lawrence<\/figcaption><\/figure>

The primary is estimated to be 2.4 times as massive as the Sun, while the secondary has about 85% of the Sun\u2019s mass.<\/p>

The orbital period is 8.62 years and at the periastron (where both stars were at minimum separation) in 2011, they appeared separated by just 50 milli-arcseconds.\u00a0<\/p>

Observing Rasalhague<\/strong><\/h2>

Rasalhague appears to shine at mag. +2.08 and has a spectral classification<\/a> of A5 III \u2013 a giant star (the \u2018III\u2019 part) that has exhausted the hydrogen fuel at its core.<\/p>

Its companion is redder, with an estimated spectral class of K5 V.<\/p>

The star is a fast rotator too, spinning at 240km\/s. For comparison the Sun\u2019s rotational velocity is a rather leisurely 2km\/s.<\/p>

\"Photo
Photo showing star Rasalhague in the night sky. Credit: Bernhard Hubl \/ CCDGuide.com<\/figcaption><\/figure>

At such a speed Rasalhague is close to its break-up speed of 270 km\/s and will be bulging noticeably at its equator.<\/p>

An effect known as \u2018gravity darkening\u2019 will also be causing the star\u2019s poles to be hotter than its equator.<\/p>

Current estimates suggest the equatorial radius is 20% larger than the polar radius.<\/p>

We get to see the star almost sideways on, its rotational axis being inclined to our line of sight by around 88\u02da.<\/p>

If you’ve observed or photographed Rasalhague, share your observations and images with us by emailing contactus@skyatnightmagazine.com<\/a>.<\/em><\/strong><\/p>

This article appeared in the May 2019 issue of BBC Sky at Night Magazine.<\/em><\/strong><\/p> <\/body><\/html>\n

","protected":false},"excerpt":{"rendered":"

By Pete Lawrence Published: Tuesday, 08 October 2024 at 10:05 AM At the top of Ophiuchus, the Serpent Bearer, representing his head, is the star Rasalhague (Alpha (\u03b1) Ophiuchi). Close by is Rasalgethi, the head of another giant in the stars, located in the constellation Hercules, the Strong Man. Rasalhague is a binary star system, […]<\/p>\n","protected":false},"author":24,"featured_media":64500,"template":"","categories":[1],"acf":{"readingTimeMinutes":"2"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/10\/rasalhague-brightest-star-in-ophiuchus.jpg",1200,825,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/10\/rasalhague-brightest-star-in-ophiuchus-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/10\/rasalhague-brightest-star-in-ophiuchus-300x206.jpg",300,206,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/10\/rasalhague-brightest-star-in-ophiuchus-768x528.jpg",768,528,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/10\/rasalhague-brightest-star-in-ophiuchus-1024x704.jpg",800,550,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/10\/rasalhague-brightest-star-in-ophiuchus.jpg",1200,825,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/10\/rasalhague-brightest-star-in-ophiuchus.jpg",1200,825,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":"By Pete Lawrence Published: Tuesday, 08 October 2024 at 10:05 AM At the top of Ophiuchus, the Serpent Bearer, representing his head, is the star Rasalhague (Alpha (\u03b1) Ophiuchi). Close by is Rasalgethi, the head of another giant in the stars, located in the constellation Hercules, the Strong Man. Rasalhague is a binary star system,…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/64499"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/64500"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=64499"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=64499"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}