29/01/2006

SATELLITES PART IV: CELESTRIAL MOVEMENTS

If you travel out of Wellington and up over the Rimutaka hills, then on through Masterton and on to the East Coast you come to a sweet spot on the Wairarapa Coast called Riversdale. Being an ignorant Aucklander, I’ve only just discovered the place, which has serene, sweeping beaches that gives way to gentle rolling farmland.

Landing here for a few days R & R I spent most of the time swimming, sitting on the beach and playing games with the numerous kids I was staying with. But at night, the place is gifted with next to no light pollution. The sky’s are pitch black and when there are no clouds the picture above is fantastic. The Milky Way stretches overhead in detail and all the stars visible to the naked eye are easy to spot. With little else to while the evening away apart from drinking, we engaged in a little star-gazing.

While technology was pretty much banned at the bach, we were able to smuggle in a Garmin handheld GPS unit and a Harrier smartphone. Getting the co-ordinates of Riversdale from the Garmin, we were then able to plug them into the website http://www.heavens-above.com/ to find out exactly what satellites were visible overhead.

Among the couple of dozen or so satellites that are visible in the night sky over New Zealand are the US military’s Lacrosse spy satellites, the SeaSat weather research satellite, a bunch of Cosmos rockets that have been floating around for years and the International Space Station. The latter is very large and reflects a lot of light, therefore making it easy to see with the naked eye. The website told us ISS would be visible for 35 seconds from 22.03 from 10 degrees to 80 degrees to the north-west so we studied the sky waiting for it. It didn’t show. Maybe the timing was wrong but we didn’t see it in the band specified. However we soon after did see a satellite streak straight overhead. Within a couple of hours of just looking up at the night sky I had spotted six satellites and two shooting stars. I gave up on trying to match them with the data from the website as they never appeared where they were meant to. Still, I was staggered at the number of satellite pass-overs we were able to pick up. There was an excited cry as someone from our inebriated party spotted another spot of light tearing across the sky.

What makes the satellites visible is their reflection of the sun’s light. Some are brighter than others, depending on how much light the structure of the satellite catches and how reflective the coating of the satellite is. Most of the satellites are designed to reflect as much light as possible so are coating in particularly reflective materials. A system designed by the ancient Greeks, but adapted by modern astronomers is used to determine how bright a celestial body is based on magnitude. It’s a logarithmic scale that goes from minus to plus. So the sun is incredibly bright at -26.7, the full moon, still very bright at -12.7. Most of the satellites moving over New Zealand range from -3 to +5. Those in positive territory become progressively harder to see as their rating increases until they are undetectable by the human eye at between +6 and +7. Pluto has a magnification of +14 making it visible only through powerful telescopes.

Seeing the International Space Station pass overhead and knowing there are a handful of people onboard floating in space, does send a shiver down the spine. The astronauts will be preparing for a space walk scheduled for February 3. During the operation they will jettison an old Russian space suit that will float in its own orbit around the earth for up to six weeks before being drawn into the earth’s atmosphere and burning up on its re-entry. Before it does so, radio equipment on the suit will transmit recorded messages in several languages that ham radio operators will be able to pick up. How long the transmissions last for will depend on how long the radio equipment’s batteries hold out for but it could be days or weeks. I’ll certainly be getting my father, a ham radio operator (ZL1AXS) to listen out on his rig for the empty cosmonaut’s suit circling the globe.
Nasa's ISS website has some good information about the missions being undertaken.

Thanks to Detlef for introducing me to Heavens-above.com

Wellington’s co-ordinates: ( 41.3000°S, 174.7830°E)

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