Walk­ing on Sun­shine

Science Illustrated - - EDITORIAL - An­thony Ford­ham aford­ham@next­media.com.au

or most of hu­man his­tory, the idea of “walk­ing on the Moon” was more or less the same as the idea of “walk­ing on the Sun”. We al­ways knew the Moon was dif­fer­ent to the Sun, but it was still the less-bright light that comes out at night­time. We thought it was a source of light it­self, rather than merely a re­flec­tor. We took it for granted.

More than that ac­tu­ally, be­cause to our an­ces­tors, the way the Moon changes shape over the course of a month, and the way th­ese phases af­fect ev­ery­thing from the size of the tides to when var­i­ous plants bloom and an­i­mals mi­grate, wasn’t so much a source of won­der as a source of an ex­tremely re­li­able and pre­dictable celestial clock. The Moon. Not much of a name is it? Most cul­tures name it ei­ther af­ter some kind of mi­nor de­ity (of­ten fe­male), while oth­ers are more prac­ti­cal or pro­saic. For in­stance, you may have heard that the word “month” comes from “moon”, since a month is more-or-less the time it takes for a new Moon to fully wax and then wane. But ac­tu­ally, it’s the re­verse - “moon” comes from words mean­ing month and, in­ter­est­ingly, “to mea­sure”.

That’s be­cause for thou­sands of years, the Moon’s main job was to let farm­ers know when to sow and when to har­vest. An­i­mal reproduction is also linked to a lu­nar cy­cle - in­deed, so is our own - so hav­ing a big bright disc in the sky ev­ery night that gets big­ger and smaller over time to let you know when to get things ready for lit­tle lambs or lit­tle pig­gies (or even lit­tle peo­ple) has, in many ways, been key to our suc­cess.

The irony? Our Moon is one of the dark­est in the So­lar Sys­tem. It’s albedo - the amount of sun­light it re­flects - is just 0.12. That

Fmeans only 12% of the sun­light that hits it gets bounced back at us. Or about the same amount as a road covered in black as­phalt.

Com­pare that to Saturn’s moon Ence­ladus. Its icy sur­face has an albedo of 0.99 - it re­turns al­most all the light that hits it. Were Encedalus in or­bit around Earth, at the same dis­tance as the Moon, it would be a tiny but blind­ing and blaz­ing coin, about a tenth the ap­par­ent size of the real Sun (and 0.14 the ac­tual size of our cur­rent Moon).

Of course, albedo is an ideal num­ber. The Moon ac­tu­ally does look a bit brighter than its albedo sug­gests, es­pe­cially due to some­thing called the “op­po­si­tion effect”. When the Moon is full, that means the Sun is be­hind us as we view the Moon. The light comes straight back at us. When the Moon ap­pears as a cres­cent, that means the Sun is off to the side (well, the Moon is off to the side re­ally, be­cause it’s or­bit­ing Earth, and the Earth it­self spins and or­bits the Sun and... look, it gets com­pli­cated). Point is, the Moon looks plenty bright to us!

Even­tu­ally of course, hu­mans got around to in­vent­ing the tele­scope. If you’ve never looked at the Moon through a prop­erly pow­er­ful tele­scope, it’s worth try­ing to ar­range it. To the naked eye, even on a very clear night, the Moon looks like a disc. In a tele­scope, it bulges out to­ward you. It’s re­ally, al­most con­frontingly ob­vi­ous that the Moon is a huge, three-di­men­sional thing.

And all along the dark edge you can see what are un­mis­tak­ably moun­tains. There is a coun­try up there, a place of des­o­late beauty. A land­scape that, be­cause of the lack of at­mos­phere and erod­ing wa­ter cy­cle, is - at hu­man scale - grander and more epic than any­thing here on Earth.

It’s def­i­nitely time to go back.

Newspapers in English

Newspapers from Australia

© PressReader. All rights reserved.