Quest for unknown planets at the Stardome

The clear skies of the Indian summer have created a gruelling research schedule at the Stardome Observatory. One exciting international project we are part of involves a search for planets orbiting stars thousands of light years from Earth.

While such planets are too far off to be seen directly by any telescope, their gravitational field gives them away. The gravity of stars creates a distorting lens that bends light. If there is a planet in orbit around the star, the gravity lens is further warped in a particular way.

All stars in our galaxy are in motion, so occasionally a star with an attendant planet may pass exactly between us and a more distant star. Then for a few days the light from the distant star is magnified by the combined gravity lens, causing it to appear brighter - sometimes hundreds of times brighter!

When the Stardome is alerted to one of these stellar alignments, we accurately monitor the brightness change of the aligned stars throughout the night. Our measurements are then combined with those of other observatories to develop a complete picture of the event.

Analysis of these events provides the only known method for detecting distant planets of comparable size to the Earth. So far this year we have contributed to five of these alerts.

Of the planets that orbit our own star, the Sun, Saturn is in Gemini and is now setting in the west at 10pm.

The most eye-catching of the planets at present is Jupiter, now within the constellation of Virgo. It is the brightest object in the eastern sky just after sunset and is well placed for viewing most of the night. By 10.15pm Jupiter will be due north and a little over halfway up from the horizon.

Jupiter's four largest moons, looking like faint stars in a line near the planet, can be seen with a small telescope or even binoculars. Sometimes one or more of the moons may be hidden by the planet or be in eclipse within the planet's shadow.

The constellations of the month are Scorpius and Sagittarius, which are rising in the east from sunset and are high overhead by midnight. Here we are looking towards the huge central bulge of the Milky Way galaxy and seeing the combined light of the billions of stars crowding the region. The star "clouds" of Sagittarius are stunning when seen from a dark, country location but can also be seen from the city on a moonless night.

* Dr Grant Christie is former chairman of the Auckland Observatory and Planetarium Trust Board. The Stardome observatory is open Wednesday to Saturday.