{"id":44493,"date":"2023-05-10T07:47:06","date_gmt":"2023-05-10T07:47:06","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=118544"},"modified":"2023-05-10T08:32:29","modified_gmt":"2023-05-10T08:32:29","slug":"observe-venuss-phases-as-the-planet-approaches-50-illumination","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/observe-venuss-phases-as-the-planet-approaches-50-illumination\/","title":{"rendered":"Observe Venus\u2019s phases as the planet approaches 50% illumination"},"content":{"rendered":"

Venus changes appearance quite dramatically as it orbits the Sun. It\u2019s now approaching 50% lit (dichotomy). <\/p>

By Pete Lawrence\n \t\t<\/p>

Published: Wednesday, 10 May 2023 at 12:00 am<\/p>

\n\n

Venus is an inferior planet. This doesn\u2019t mean it\u2019s a lesser world than ours, it\u2019s simply a reference to the size of its orbit.<\/p>\n

Inferior planets<\/a> have smaller orbits than Earth, superior planets larger orbits. Mercury and Venus are inferior planets, the rest are superior.<\/p>\n

Inferior planets are interesting to observe as their apparent sizes wax and wane noticeably over time and they show a full set of phases.<\/p>\n

In 2023, Venus reaches greatest eastern elongation on 4 June, appearing 45.4\u00b0 to the east of the Sun and brilliant in the evening twilight.<\/p>\n

The planet should appear at 50% phase, known as dichotomy, on this date.<\/p>\n

This means that May is a great chance to observe Venus before it fades<\/a>.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Venus\u2019s changing appearance as it orbits; it\u2019s now approaching 50% lit (dichotomy). Credit: Pete Lawrence<\/span><\/figcaption><\/div>\n

The run up to dichotomy, say from 10 days before, is a good time to start making phase estimates and they\u2019re really easy to do.<\/p>\n

Simply observe Venus through the eyepiece, noting whether the planet\u2019s terminator is straight or curved.<\/p>\n

If straight, this is dichotomy. If curved, estimate how far across the diameter of Venus \u2013 at right angles to the terminator<\/a> \u2013 the terminator extends.<\/p>\n

As an example, if the terminator stretched one-third across the diameter of Venus, this would be a 33% phase.<\/p>\n

Starting to observe early gives you more experience at making accurate assessments.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
An image showing the phases of Venus, captured by Roger Hutchinson, London, UK, 25 March 2017. This image won the Planets, Comets & Asteroids category of the 2017 Astronomy Photographer of the Year competition.<\/span><\/figcaption><\/div>\n

It\u2019s easy to look and record \u201850%\u2019 at a first glance, but is it really 50% or perhaps a little above or below that?<\/p>\n

Why bother to do this? Surely the geometric position of Venus will give a precise and predictable value for its phase?<\/p>\n

Actually, this is not the case. The planet\u2019s thick atmosphere interferes with the apparent phase, giving rise to the \u2018phase anomaly\u2019, an effect that makes dichotomy appear earlier than it should when Venus is in the evening sky.<\/p>\n

How early? Well, that\u2019s up to you to find out!<\/p>\n

Let us know how you get on by emailing us at contactus@skyatnightmagazine.com<\/a>.<\/strong><\/em><\/p>\n

This guide originally appeared in the May 2023 issue of BBC Sky at Night Magazine.<\/strong><\/em><\/p> <\/body><\/html>\n

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