Stargazers across the globe now have one more reason to keep their eyes on the heavens with the successful docking between China's two spacecraft. The Shenzhou-8 docked with China's first space lab module, the Tiangong-1, early Thursday morning after being launched into space Tuesday from the Jiuquan Satellite Launch Center in the deserts of northwest China.

The two new man-made objects are bound to attract satellite observers as an alternative to the International Space Station (ISS) that took shape over the last 13 years. Both of the spacecraft, like the ISS, are visible to the naked eye when the sky is clear.

Yu Jun, an amateur astronomer from Beijing, took a photograph of the Tiangong-1 as it passed over the city around 5 a.m. on Oct. 25. Yu took a long-exposure photo by stacking 15 frames, each of which was exposed for 8 seconds, creating a striking image of the spacecraft's path.

"The Tiangong-1 showed up on time! Although it was not as bright as was forecasted, it is definitely visible to the naked eye," he said.

"The Shenzhou-8 and Tiangong-1 are like two bright and fast-moving stars in the sky," said Zhu Jin, curator of the Beijing Planetarium. Zhu drove from Beijing to Inner Mongolia to witness the launch of the Shenzhou-8 due to the capital's poor air conditions.

Satellites become visible only when they are exposed to sunlight and the observer is in deep twilight or darkness. The best viewing times are shortly after dusk or before dawn, when there is still enough sunlight to reflect off of the spacecraft's surfaces.

"It's a solid light, not blinking like an airplane," Zhu said, adding that the apparent brightness of the spacecraft may change depending on weather conditions and altitude.

Kevin Fetter, a Canadian from Brockville, happened to catch Tiangong-1 on Oct. 28 while observing a fly-over of Italy's SkyMed-2 satellite with a low light security camera.

Tiangong-1 is a larger and brighter object than the Italian satellite, according to the 16-second video footage released on the website, www.space.com.

Astronomers measure the brightness of stars in terms of magnitude, with brighter stars having lower magnitude. Zhu said the Tiangong-1, when in best weather conditions and altitude, shines as brightly as a star with a magnitude of 2, or the same magnitude as Polaris, the north star.

Orbiting Earth at an altitude of 343 km and at a speed of 7.8 km per second, the Tiangong-1 takes about an hour and a half to finish one orbit. By the time it docks with the Shenzhou-8, the Tiangong-1 has completed 542 orbits.

Zhu said stargazers will have an opportunity to see both of the spacecraft in a double flyby after the docking procedure is completed. The spacecraft will remain attached to each other for 12 days after the first docking is finished, after which a second docking will be attempted.

The first docking procedure was not visible to the naked eye as the two craft were in the Earth's shadow during the process. However, the second docking procedure may be visible, as the craft will be out of the Earth's shadow at that time, Zhu said, adding that the magnitude of the combined craft is expected to be below zero, or the magnitude of Vega.

The docking mission will be followed by the launch of the Shenzhou-9 and -10 spacecraft in 2012, which are also expected to dock with the Tiangong-1. At least one of the two spacecraft will be manned.

The space docking tests and experiments will provide crucial experience for China's construction of a 60-metric-ton permanent manned space station around 2020.

Source: Xinhua News Agency