What are iridium flashes, and why should you rush to see them
Eran Ofek
Photo: Asaf Brewald
This iridium flash, which looks like a meteor, was photographed at Mitzpe Ramon, above the Weiss Observatory
About 10,000 satellites and fragments of satellites are currently in orbit around the Earth. Some of them can be seen with the naked eye. Satellites are visible when they reflect sunlight. When the satellite is hidden in the Earth's shadow, it cannot be seen. Since most satellites orbit the Earth in a low orbit, whose height above the ground is less than a tenth of the Earth's radius, they can only be seen at the beginning of the night (after sunset) or at the end of the night (before sunrise). Only then is a satellite passing over the viewer illuminated by the sun. If the same satellite passes over the viewer at midnight, the satellite will be deep in the Earth's shadow, not illuminated by the Sun, and therefore will not be visible.
The International Space Station, the Mir Space Station and the Space Shuttle are some of the brightest satellites that can be seen from Earth. Other interesting satellites to watch are the Iridium satellites of the Motorola company. As part of the Iridium project, dozens of satellites were launched into low orbit around the Earth that were supposed to be used as telephone exchanges in space - a kind of cellular network that would cover the entire Earth all the time. This project was supposed to provide an answer for those who want to conduct cell phone calls from Antarctica, from the sea or from airplanes. But the project, which cost billions of dollars, went bankrupt. The reasons for this were the spread of local cellular networks, the high price of satellite cellular telephones and the high cost of phone calls on this network.
As the iridium satellites orbit the Earth, the antennas on them can function like large mirrors that reflect sunlight. When this phenomenon occurs, the observer on Earth will see a faint point of light in the sky quickly brighten, become within a few seconds the brightest star in the sky (except for the Sun and the Moon), and fade immediately after. This phenomenon is called iridium flashes. This is a local phenomenon, and it can be seen at any given moment only from certain and extremely limited areas on the planet. A flash that will be seen from Tel Aviv will not necessarily be seen from Bat Yam.
On the website .heavens-above.com www you can find the appearance times of the iridium flashes, and their direction in the sky, as well as many other satellites, including the International Space Station. Those who want to see the iridium flashes are advised to hurry, before Motorola drops the iridium satellites into the sea.
{Appeared in Haaretz newspaper, 13/12/2000}
iridium.jpg
Without a telescope, with excellent timing
Photo: NASA
The International Space Station. Glowing wings
An astronomy enthusiast photographed the International Space Station Alpha with a telescope while it hovered over the state of Washington, USA, September 2002
The International Space Station can now be seen from Earth, without special equipment
The International Space Station, which is being built about 400 km from Earth, is quickly becoming one of the brightest objects in the sky. Last week, a huge system of wings for absorbing solar energy was added to it, measuring about 70 meters by about 12 meters (the space shuttle whose astronauts carried out the work returned to Earth the other day), and now, if you know in advance at what angle relative to the horizon the station is, and at what Wait a minute it will be possible to notice it, you can see the station from Earth without using a telescope. According to NASA, the American space agency, only Venus, Jupiter, the star Sirius and a few other celestial objects are brighter than the station.
The station, which is being built by 16 countries led by the United States and Russia, now weighs 97.5 tons and includes three central components (modules) in which the air pressure is regulated, and two of which were equipped with wings to absorb solar energy (the third component is a "Soyuz" space vehicle). The wings, which bloom in gold and blue colors, increase the chance of seeing the station from Earth.
When the station is completed, in 2006, it will have four solar wing systems, which will cover an area of about 4 dunams and make the spacecraft appear almost as bright as the moon. The US space agency and astronomy enthusiasts provide information to help people see the station online at spaceflight.nasa.gov/station. In the section called "RealTime Station Data", website visitors can upload a map showing where the station is currently located, or find out what is the best time to watch it from where they live.
The site presents information on the possibility of watching the space station from more than 200 cities around the world, most of them in the USA. Today, for example, New Yorkers will be able to see the station for about two minutes, from 17:37 to 17:39, if they look in the south-southwest direction at an angle of 67 degrees above the horizon.
The astronomical journal "Telescope & Sky" also presents information that helps locate the station in the sky. The website address of the journal is www.skypub.com. When you click on "Satellite Observing Sights/", you get predictions of the time and angle at which the station will be visible from 250 cities in North America and from 250 other cities around the world.
New York Times
{Appeared in Haaretz newspaper, 13/12/2000}
