International Space Station

Whilst waiting for the summer storms to turn up, some of the PWL team like to head out and capture the many interesting things that can be see in the night sky. Anything from stars, comets, meteors and aurora’s are on the menu. But lets start with satellites…

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Image Credit: NASA-International Space Station

The International Space Station (ISS) is a space station, or a habitable artificial satellite in low Earth orbit. It is a modular structure whose first component was launched in 1998. Now the largest artificial body in orbit, it can often be seen at the appropriate time with the naked eye from Earth. There a number of apps and websites that can tell you when and where the ISS will pass over (see below) and it often passes right over Perth.999938_10152174981729419_904539812_n     BGRIWDZCAAAeE3w
Image Credit: Commander Chris Hadfield / Perth on the Swan to the sea, Western Australia (@Cmdr_Hadfield – twitter)

The image above is just one of many that astronaut Chris Hadfield took as he orbited around the earth in the ISS.

The ISS travels at an average speed of 27,724 km/hour, and completes 15.50 orbits per day, with a with a minimum mean altitude of 330 km and a maximum of 410 km.

PWL Admin Grahame captured this image using a 12” Skywatcher on 22nd Jan 2014.
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Image Credit: Grahame Kelaher / Perth Weather Live

The following image was captured by PWL Chaser Dan Searle on 22nd Jan 2014. You can see the ISS as it passes through the frame during a long exposure. 1558511_10203005664088286_231076188_n copy
Image Credit: Dan Searle / Perth Weather Live

You can find out about the ISS at the NASA site here.

You can check out the next best time to see the ISS in Western Australia here.

Happy spotting.

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Willy-Willy, Dust Devil or Cockeyed Bob?

What you call them will depend on where in the world you come from. Willy-Willy, Dust Devil, Cockeyed Bob, Whirlwind and Sand Auger are just some of the names they go by. But how do they form? And are they the same as a tornado? Well, not really. Although they both have a rotating vortex, willy-willy’s are fair weather events. Tornadoes are formed in thunderstorms, super-cells or cold fronts. Water spouts are different again (see article here).
Willy-willy’s form when hot air near the ground rises quickly through a layer of cooler air above it. If conditions are just right, the rising air can begin to rotate.

As the air rapidly rises, the column of warmer air is stretched vertically and more warm air rushes in along the ground to the bottom of the newly forming vortex. As more warm air rushes in toward the developing vortex to replace the air that is rising, the spinning effect becomes further intensified and self-sustaining.  As the warm air rises, it starts to cool, losing its buoyancy. This cooler air then descends outside the core of the vortex. This cool air returning to the ground acts as a balance against the spinning warm-air outer wall and keeps the system stable.

dustdevil-jpgImage Credit: unknown

The spinning effect, along with surface friction, produces a forward momentum. Usually, willy-willy’s are very small and weak, often less than 1 metre in diameter with maximum winds speeds averaging about 70 km/h. Most dissipate less than a minute after forming. But occasionally,  they can reach a diameter of up to 90 metres with winds in excess of 100 km/h. If the conditions are right they can last for 20 minutes or more before dissipating. Willy-willy’s can suddenly just ‘disappear’ leaving the dust they were carrying to float to the ground. The following image shows a large willy-willy near Port Hedland. The stack on the left is 116m high!

1385801_588310904543459_1642485368_nImage Credit: ©Troy Bourne / Perth Weather Live

Interestingly, unlike tornadoes or cyclones, willy-willy’s will rotate either clockwise or anti-clockwise. Due to their size, the earth’s rotation has no effect of the direction of the spin and each direction occurs with equal frequency.

Even more interestingly, willy-willy’s have been observed on the surface of Mars! Check it out here.

1116518822_13678-4_dd_enhanced_486a-A496R1_brImage Credit: Courtesy NASA/JPL-Caltech

Here are some more images sent into us by PWL viewers:

1468555_614120531962496_1843613164_nImage Credit: ©Dean Thompson / Perth Weather Live.  This image was captured by Dean on his phone , not far from Roy Hill, in Western Australia’s Pilbara region..

960197_614319521942597_1045358762_nImage Credit: ©Name Supplied / Perth Weather Live. Another image from the North West of Western Australia.

This article is a modified version of http://en.wikipedia.org/wiki/Dust_devil and is shared under the Creative Commons Attribution-ShareAlike License. All images remain © of the owners.

Contrails v’s Chemtrails

contrail_19I was in the process of putting together an article on the much debated Contrail v’s Chemtrail issue… but somewhere at about page 15 I stopped. Why? Because I couldn’t be bothered! (sorry if my honesty offends you).

So instead, here is a collection of links that I think will help to inform you. I make no apologies for sitting firmly in the contrail camp. Of course, you are entitled to your opinion.

These links will open a new page.

 

**NOTE**  I wouldn’t believe everything you read on Wiki type sites as they are open to being edited by anyone, but you can find some great articles in the reference section at the bottom of each article.

The Smell Of Rain

P1060387We often see comments on the PWL page about how much people love the ‘smell of rain’… the distinctive scent which accompanies the first rain after a long dry period.  Have you ever wondered what that smell is? Well, it’s got a name… Petrichor.

The word comes from two Greek words, petros, meaning stone and ichor, referring to the fluid that flows in the veins of the gods in Greek mythology.

The term was first used in 1964 by two Australian researchers in an article that they wrote in a nature journal. In the article, the authors describe how the smell derives from an oil exuded by certain plants during dry periods, which is absorbed by clay-based soils and rocks. When it rains, the oil is released into the air. In another article some time later, they showed that the oil seems to delay seed germination and early plant growth. It seemed that the plants produced the oil in order to safeguard the seeds from germination during long dry spells or periods of drought.

I don’t know about you, but when I catch a whiff of the ‘smell of rain’… many childhood memories of growing up in the bush come flooding back.

This information is adapted and used with permission under Creative Commons Attribution ShareAlike License.  Image ©Matt Fricker Photography/Perth Weather Live