New Delhi: Sky gazers will get an opportunity to view Saturn up close this evening when the planet reaches opposition. This will put it among the highlights of the October night sky.
The event brings the ringed planet closest to Earth for the year and makes it visible for much of the night. However, there is another phenomenon that makes the occasion particularly interesting for observers: the Seeliger effect, or opposition surge.
According to astronomers, opposition occurs when Earth passes between the Sun and an outer planet. From Earth, the planet then appears opposite the Sun in the sky.
As a result, Saturn rises around sunset and remains visible for most of the night. NASA has listed October 4 as one of October’s major skywatching events, noting that the geometry makes Saturn especially well placed for observation, as reported by Hindustan Times.
Saturn reaches opposition around 5.30 pm IST. At opposition, Saturn will be about 1.26 billion kilometres from Earth and will shine at around magnitude 0.3, making it readily visible to the unaided eye when above the horizon. Its apparent disk will measure about 19.7 arcseconds across through a telescope, according to Earth sky.
For skywatchers in India, Saturn rises at around 6.11 pm on October 4 and reaches its highest point in the sky around 12.17 am, before setting around 6.23 am on October 5. It will be visible for almost the entire night.
The Seeliger effect refers to the increase in brightness of Saturn’s rings around opposition. The phenomenon is named after German astronomer Hugo von Seeliger, who studied the effect in the late 19th century.
This happens because of the unusual geometry of sunlight on Saturn’s rings and Earth around opposition. Saturn’s rings consist of countless particles, primarily made of water ice. Under normal viewing conditions, these particles cast tiny shadows on one another. Near opposition, however, the Sun is almost directly behind the observer from the perspective of the rings.
That means many of the shadows cast by the ring particles fall directly behind those particles and become hidden from Earth. More of the visible ring surface is therefore directly illuminated, producing an increase in apparent brightness.
Saturn can be spotted without optical equipment as a bright, steady point of light. From India, skywatchers can look towards the eastern sky after sunset and follow the planet as it climbs higher through the evening.
A telescope, however, offers a very different view. Even a small amateur telescope can reveal Saturn’s rings, while larger instruments can show features such as the Cassini Division (the dark gap between Saturn’s rings) and some of the planet’s brighter moons under favourable conditions.