For more advice, read our guide to astronomy for beginners<\/a><\/strong><\/em><\/p> In the colder months, my favourite sight on a clear night is the familiar Orion constellation<\/a>, and it\u2019s within this pattern of stars that we can see a classic example of colours in the night sky.<\/p> Look carefully at the star Betelgeuse<\/a> \u2013 Orion\u2019s right shoulder (assuming he\u2019s facing us) \u2013 and you\u2019ll notice that it has an orange-red tinge to it.<\/p> Compare this with the star Rigel<\/a>, on Orion\u2019s left foot, and you\u2019ll see that Rigel appears much more blue-white.<\/p> Why is this? What causes the different colours of stars<\/a>?<\/p> The reason stars look different colours – some are red, some are blue – is all to do with their temperatures.<\/p> It\u2019s the opposite to what you might think: red stars like Betelgeuse are actually cooler than blue stars like Rigel.<\/p> I say cooler, but bear in mind that the surface temperature of Betelgeuse is still around 3,200\u00baC, compared to Rigel\u2019s 10,700\u00baC.<\/p> The colour of stars may seem counterintuitive based on our everyday experiences of linking colour to temperature (think colour-coding on taps: red for hot and blue for cold) but it\u2019s the same principle as when metal is heated in a forge.<\/p> First you\u2019ll see it start to glow red, then as its temperature increases the metal glows a blue-white.<\/p> A pair of binoculars or a telescope can reveal even more colour in the night sky.<\/p> Sticking with Orion, a small telescope shows the fuzzy \u2018star\u2019 in the middle of his sword is not a star at all, but the Orion Nebula<\/a>, a region where new stars are being born.<\/p> Here the gas is being lit up by radiation from the young, newly formed stars, transferring energy to the atoms in the gas and \u2018exciting\u2019 them.<\/p> Due to the different atomic structures of the elements in the Orion Nebula, we see different colours when we look at it through a telescope, including pinky-red from hydrogen and green from oxygen.<\/p> In fact, every element in the periodic table will emit a unique pattern of colours when excited, and this is the element\u2019s spectrum.<\/p> In the same way as you can split white light up into a rainbow using a prism, splitting observed light up into its spectrum is a technique called spectroscopy<\/a>.<\/p> Spectroscopy allows astronomers, for example, to identify what elements are present within a nebula<\/a>.<\/p> A pioneer in the field of spectroscopy work was Margaret Huggins, an unsung hero of astronomy.<\/p> She worked with husband William in the late 19th century to catalogue the spectra of stars<\/a>, galaxies<\/a> and nebulae.<\/p> Today, spectroscopy is perhaps the most powerful tool in an astrophysicist\u2019s toolkit.<\/p> It enables us to do everything from detecting exoplanets<\/a> to measuring the expansion of the Universe<\/a> and inferring the existence of dark matter<\/a> in galaxies.<\/p> All this from analysis of the colours in the night sky.<\/p> This article originally appeared in the February 2018 issue of <\/strong><\/em>BBC Sky at Night Magazine<\/strong>.<\/strong><\/em><\/p> <\/body><\/html>\n The Universe is awash with colour, but what causes some stars to be red and others to be blue? <\/p>\n","protected":false},"author":24,"featured_media":53020,"template":"","categories":[1],"acf":{"readingTimeMinutes":"4"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/01\/why-some-are-stars-red-and-some-stars-are-blue.jpg",1200,800,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/01\/why-some-are-stars-red-and-some-stars-are-blue-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/01\/why-some-are-stars-red-and-some-stars-are-blue-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/01\/why-some-are-stars-red-and-some-stars-are-blue-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/01\/why-some-are-stars-red-and-some-stars-are-blue-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/01\/why-some-are-stars-red-and-some-stars-are-blue.jpg",1200,800,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/01\/why-some-are-stars-red-and-some-stars-are-blue.jpg",1200,800,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":"The Universe is awash with colour, but what causes some stars to be red and others to be blue?","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/53019"}],"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\/53020"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=53019"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=53019"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"Colour](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2020\/02\/Betelgeuse_Rigel-cf58bef-e1601297457983.png\" "\\"\\"\/")
The chemistry behind stars’ colours<\/strong><\/h2>
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