{"id":49768,"date":"2023-10-09T10:44:25","date_gmt":"2023-10-09T10:44:25","guid":{"rendered":"http:\/\/4d0f4943-69cb-4757-8eab-631742c64c16"},"modified":"2023-10-09T12:32:30","modified_gmt":"2023-10-09T12:32:30","slug":"see-gruithuisens-lunar-city-on-the-moon","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/see-gruithuisens-lunar-city-on-the-moon\/","title":{"rendered":"See Gruithuisen’s Lunar City on the Moon"},"content":{"rendered":"

Can you spot this famed ‘city’, which is actually a lunar trick of the light? <\/p>

By Pete Lawrence\n <\/p>

Published: Monday, 09 October 2023 at 10:44 AM<\/p>

\n\n

If nothing else, Gruithuisen\u2019s Lunar City sounds rather grand.<\/p>

The reality is not quite so impressive, but this is still an interesting clair-obscur effect on the Moon<\/a> to track down.<\/p>

In order to see the Gruithuisen\u2019s Lunar City on the Moon, the position of the evening terminator (the line dividing light and shade on the lunar surface) has to be right.<\/p>

This is measured by a value known as co-longitude and can be obtained for a given date and time from free software such as WinJupos<\/a> and the Virtual Lunar Atlas<\/a>.<\/p>

Here we need a co-longitude of 185.0\u00b0 with the Moon just past last quarter.<\/p>

For more info, read our guides on how to observe the Moon<\/a> and how to photograph the Moon<\/a><\/em><\/strong><\/p>

Last Quarter Moon by Andrew McNaught, Gloucestershire, UK. Equipment: Sky-watcher ST102 Refractor, i-Nova NNB Cx OSC CCD, Skywatcher EQ8 Mount.<\/figcaption><\/figure>

What is Gruithuisen’s Lunar City?<\/strong><\/h2>

It’s not a real city of course, but rather a lighting effect making a small section of the Moon appear to have linear streets and buildings.<\/p>

The feature was named at a time when it was thought the Moon was populated.<\/p>

It was discovered in 1824 by Franz von Paula Gruithuisen, who made multiple observations of it, calling the city \u2018Wallwerk\u2019.<\/p>

How to find Gruithuisen’s Lunar City<\/strong><\/h2>
\"An
An image of the Moon showing how to find the effect known as Gruithuisen’s Lunar City. Credit: Pete Lawrence<\/figcaption><\/figure>

Finding Gruithuisen’s Lunar City can be challenging.<\/p>

The \u2018city\u2019 is located using giants crater Copernicus<\/a> (93km) and crater Eratosthenes (60km).<\/p>

Imagine them forming one side of a large isoceles triangle.<\/p>

The other point is marked by the smaller 27km crater M\u00f6sting, further to the south and near the terminator<\/a>.\u00a0<\/p>

Starting at M\u00f6sting, head back along the line towards Eratosthenes.<\/p>

For more like this, read our guides on the best features to observe on the Moon<\/a> and underrated Moon features<\/a><\/em><\/strong><\/p>

\"Copernicus
Copernicus and Eratosthenes by Michael K Jamieson, Snitterby, Lincolnshire, 31 May 2020.Equipment: ZWO ASI 224MC colour camera, Meade LX90 SCT.<\/figcaption><\/figure>

About one-fifth of the way you\u2019ll arrive at heavily eroded 35km Schr\u00f6ter, a crater that appears to have lost its southern rim.<\/p>

Keep going towards Eratosthenes and the next obvious crater is Schr\u00f6ter W, which has a diameter of 10km.<\/p>

Schr\u00f6ter W has a smaller 3km crater, Schr\u00f6ter A, inside it which will be in darkness when the terminator is nearby.<\/p>

The \u2018streets\u2019 of Gruithuisen\u2019s City appear from the shadows cast in the highland region to the north and east of Schr\u00f6ter W.<\/p>

Have you managed to find or even photograph Gruithuisen’s Lunar City? Let us know by emailing contactus@skyatnightmagazine.com<\/a>.<\/em><\/strong><\/p> <\/body><\/html>\n

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