How do the Moon’s features compare with Earth?

The Moon looks great through a scope, but at over 380,000km away it's hard to get a sense of how big its features really are. The Sky at Night's Pete Lawrence reveals how lunar features compare to Earth's landmarks

A comparison of the size of the UK and Ireland with the surface of the Moon. Credit: Pete Lawrence

Have you ever wondered how big the Moon’s features are compared with some of the most famous features on Earth? Here, we take a look at some of the standout lunar phenomena and how they size-up when put alongside some of Earth’s familiar natural sights.

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1

The Moon vs the UK and Ireland

The Moon’s diameter is 3,475km, roughly  a quarter of Earth’s.

The straight-line distance between Land’s End in England and John o’ Groats in Scotland is 960km, roughly a quarter of the Moon’s diameter.

From Earth, the Moon has an apparent diameter that varies between 33.6 and 29.4 arcseconds, with a mean value of 31.1 arcseconds.

For simplicity’s sake, the Moon’s apparent diameter is normally described as being half a degree.

2

Tycho vs the Shard

A comparison between crater Tycho and the Shard. Credit: NASA Goddard/Arizona State University

The southern ray crater Tycho has a distinctive rim measuring 88km across, similar to the distance from central London to Oxford.

The 60km diameter M25 around London would just fit across Tycho’s inner floor.

The crater has a 2,000m high central peak, roughly 6.5 times the height of the 310m-tall London Shard.

The peak is easily visible with a small telescope.

3

The Apennines vs the Alps

The lunar Apennine mountains define the southeast border of the Mare Imbrium.

The range is 600km long, containing peaks that rise to over 5km.

The Alps on Earth are 1.5 times longer at 960km, with the highest peak – Mont Blanc – rising to 4.8km.

The Apennines were formed when material was pushed aside by the impact that formed the Imbrium Basin.

4

Hadley Rille vs the Thames

Hadley rille. Credit: Pete Lawrence

Hadley Rille is a crack in the lunar surface formed when the ceiling of an ancient, submerged river of lava collapsed.

Requiring at least an 8-inch scope to see, its main part is 80km long, with a maximum width of 2,000m and depth of 370m.

By comparison, England’s River Thames is 346km long in total, and 252m wide when passing the Houses of Parliament.

In its estuary, its depth is 20m at most.

5

The Mare Crisium vs France

The Mare Crisium is a dark, oval feature seen close to the Moon’s northeastern edge.

Its 400km x 530km floor is the result of an impact with a 25km-wide body about 3.9 billion years ago.

The whole of Ireland would fit inside it, while the Mare Crisium itself would in turn fit comfortably inside France.

6

The Straight Wall vs Big Ben

The Straight Wall vs Big Ben. Credit: Pete Lawrence

The Straight Wall is a 110km linear fault.

Seen a day after first quarter its shadow gives the impression of a sheer cliff, but its 300m height difference is actually achieved by a gentle 7° slope.

The fault’s height is roughly three times that of Big Ben’s tower.

7

Copernicus vs the Midlands

Crater Copernicus, as seen by the Lunar Reconnaissance Orbiter. Credit: NASA (image by Lunar Reconnaissance Orbiter) - JMARS

Copernicus is a ray crater to the south of the Imbrium Basin.

Its 93km-diameter rim contains a central mountain peak complex rising to 1,200m – four times the height of the London Shard.

If Copernicus was centred on Birmingham, the rim would reach out almost as far as Leicester, while the longest ejecta rays would reach all the way to Orkney.

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This article originally appeared in the September 2012 issue of BBC Sky at Night Magazine. Pete Lawrence is an experienced lunar observer and a presenter on The Sky at Night.