Her pale fire she snatches from the sun

Shakespeare writes “the moon’s an arrant thief, and her pale fire she snatches from the sun” (Timon of Athens, Act 4, Scene 3). He is, of course correct. The moon merely reflects sunlight, and produces no light of its own. One way of telling this is that moonlight actually displays the same telltale absorption spectrum as sunlight:

Our eyes tend to perceive moonlight as “blueish” or “silvery,” but that is because of the way our eyes work at low light levels. Long-exposure photographs under moonlight, like this one, look much like daytime shots:

Anaxagoras (499–428 BC) seems to have been the first to discover that the moon shines only by reflected light:

Anaxagoras also explained that solar eclipses occur when the moon moves between the earth and the sun. Total solar eclipses are dark precisely because the moon produces no light of its own:


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Travelling across Australia: Ten things to spot

On October 8, teams in the World Solar Challenge begin their race from Darwin to Adelaide. Here are 10 things for travellers across Australia to look out for.

1. The Magellanic Clouds

The Magellanic Clouds are two small galaxies – at 160,000 light-years and 200,000 light-years, the nearest visible galactic neighbours of our Milky Way. They can be seen in the Southern Hemisphere, away from towns. The Australian Outback is the perfect place to observe them.


The Magellanic Clouds (photo: ESO/S. Brunier)

2. The Southern Cross

The Southern Cross (Crux) is a constellation appearing on the flags of many countries in the Southern Hemisphere, including Australia. It consists of four bright stars, with a fifth being visible to the naked eye in good conditions. The constellation can be located with the aid of the pointer stars Alpha Centauri and Beta Centauri. It can also be used to determine the South Celestial Pole. The star at the “top” of the Cross (Gamma Crucis) is a red giant. The fifth star (Epsilon Crucis) is an orange giant.


The Southern Cross, pointers, and Magellanic Clouds (image: Michael Millthorn)

3. The wedge-tailed eagle

The wedge-tailed eagle (Aquila audax)) is Australia’s largest bird of prey, and a national icon. It can be seen around Australia, either in the sky, or snacking on roadkill.


Wedge-tailed eagle (photo: Fir0002/Flagstaffotos)

4. The red kangaroo

The red kangaroo (Macropus rufus) is the largest living marsupial, and is found throughout central Australia, in areas with less than 500 mm rainfall. It is an Australian national icon, as well as being a major traffic hazard at dawn and dusk.


Red kangaroos (photo: Jenny Smits)

5. The sand goanna

The sand goanna (Varanus gouldii) is a large monitor lizard, growing to about 1.5 metres. It is found across much of Australia.


Sand goanna (photo: Alan Couch)

6. The thorny devil

The thorny devil (Moloch horridus) is found in arid, sandy areas of western and central Australia. It lives mostly on ants.


The thorny devil (photo: Bäras)

7. Magnetic termites

Magnetic termites (Amitermes meridionalis) are one of two Australian termite species building mounds that align north–south. They can be found in the vicinity of Darwin. The mound orientation appears to be a temperature-control mechanism.


A magnetic termite mound (photo: brewbooks)

8. Sturt’s desert pea

Sturt’s desert pea (Swainsona formosa) grows in arid regions of Australia. It is the floral emblem of the state of South Australia.


Sturt’s desert pea (photo: Fir0002/Flagstaffotos)

9. The desert grasstree

The desert grasstree (Xanthorrhoea thorntonii) is a grasstree found in arid regions of western and central Australia. Like the other 27 species of grasstree (Xanthorrhoea spp.), it is endemic to Australia, and a symbol of the Australian landscape.


The desert grasstree (photo: Mark Marathon)

10. Opal

Opal is a gemstone form of hydrated silicon dioxide. The town of Coober Pedy in South Australia is a major source.


Opal from Coober Pedy (photo: Dpulitzer)


Silly Season in the Sky (again)

It’s apparently time for lunatic end-of-the-world prophecies again. The latest relates to a “great red dragon” in the sky (a reference to Revelation 12):

Turns out that this is a double image of Saturn, taken way back in 1983 by the Infrared Astronomical Satellite (IRAS). Saturn was then at RA 13h45m18.2s, DEC -08d13m07s.

It’s a false-colour image (i.e. not red at all), being taken at 100 microns, in the infrared region of the spectrum. But with enough spin, apparently it can be made to sound scary.

In the final version of the infrared sky survey, this artefact was blacked out, since it doesn’t reflect any actual stellar infrared sources (just a planet that moves around). Of course, that removal got the conspiracy-theory nutters going.


Mars in the Night Sky

Mars is growing brighter in the sky, appearing close to the star Antares and the planet Saturn (see NASA image above). Later this month, Mars will reach the point of closest approach, and hence largest apparent size.

For the current distance to Mars, see Wolfram’s calculator or the live diagram of the solar system at Fourmilab, which includes images (green lines show orbits below the plane of the ecliptic):

Live Solar System image


WSC: Magellanic Clouds

I have previously posted about the spectacular night sky in the Australian Outback. Among other things, visitors from the Northern Hemisphere (as well as Southern city folk) will be able to see our companion galaxies, the Magellanic Clouds. The Magellanic Clouds are only visible well away from city or town lights. They can be seen at the top of the wonderful photograph below (taken in Chile, credit European Southern Observatory):


Venus and Jupiter in conjunction

The planets Venus and Jupiter were in conjunction last night, as the photograph above (by Neal Simpson) shows. The diagram below (by the Fourmilab) shows why: although Venus is much closer to Earth (and thus much brighter), the three planets are almost in a straight line. Venus and Jupiter should still be pretty close in the sky for the next few nights.