See a lunar occultation of Porrima, 13 May 2022

Binary star Porrima in Virgo is set to be occulted by the Moon this week. Find out how you can see it.

Published: May 9, 2022 at 8:50 am
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Star Porrima, known as Gamma (γ) Virginis, is a binary star in the constellation Virgo with an orbital period of 169 years.

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Back in the early 2000s the apparent separation of the two components was so small that it was virtually impossible to split them.

Now that situation has improved somewhat and the two similarly bright stars (mag. +3.6 and mag. +3.7), appear separated by a little over 4 arcseconds.

Constellation Virgo, showing the locations of Spica and Porrima. Credit: Hubl Bernhard, CEDIC Team / CCDGuide.com
Constellation Virgo, showing the locations of Spica and Porrima. Credit: Hubl Bernhard, CEDIC Team / CCDGuide.com

The binary pair is made of two similar main sequence stars both about 38 lightyears from Earth.

Shining at mag. +2.7, Porrima can be seen with the naked eye in the ‘bowl of Virgo’, but to resolve it and see the two individual stars, you’ll need a telescope.

Lunar occultations of Porrima

From the centre of the UK, Porrima is occulted at 05:52 UT on 19 March as the sky is brightening due to the approach of dawn. Credit: Pete Lawrence
Credit: Pete Lawrence

Because Porrima lies close to the ecliptic - the imaginary line followed by the Sun across the sky - it can often be seen in a lunar occultation, whereby it disappears behind the Moon from our perspective on Earth.

One such occultation occurred on 19 March 2022 and was viewable from the UK.

The next is happening very soon. On the morning of 13 May, the 87%-lit waxing gibbous Moon will occult Porrima.

The event occurs at 01:50 BST (00:50 UT) as seen from the centre of the UK, Porrima disappearing behind the Moon’s dark limb.

This time may vary by up to a few minutes either side depending on your actual location.

An illustration showing the lunar occultation of Porrima on 13 May 2022. Times are correct for centre of UK. It's advisable to begin observing 10-15 minutes earlier to avoid missing the event. Credit: Pete Lawrence
An illustration showing the lunar occultation of Porrima on 13 May 2022. *Times are correct for the centre of the UK. It's advisable tobegin observing 10-15 minutes earlier to avoid missing the event. Credit: Pete Lawrence

The best way to see the lunar occultation of Porrima is to observe from 01:30 BST (00:30 UT), first locating the Moon and then the star.

This will ensure you don’t miss anything.

The Moon’s orbital motion keeps it moving east against the background stars. Eventually, it will have moved sufficiently far to allow Porrima to re-emerge from behind the Moon’s bright edge.

This will occur at 02:42 BST (01:42 UT) as seen from the centre of the UK, and again, it’s wise to start observing 10-15 minutes earlier than this time to make sure you don’t miss it.

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This guide originally appeared in the March 2022 issue of BBC Sky at Night Magazine.

Authors

Pete Lawrence, astronomer and BBC The Sky at Night presenter.
Pete LawrenceAstronomer and presenter

Pete Lawrence is an experienced astronomer and astrophotographer, and a presenter on BBC's The Sky at Night.

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