Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2011 June 23
See Explanation.  Clicking on the picture will download
the highest resolution version available.

Stereo Helene
Credit: Cassini Imaging Team, ISS, JPL, ESA, NASA; Stereo Image by Roberto Beltramini

Explanation: Get out your red/blue glasses and float next to Helene, small, icy moon of Saturn. Appropriately named, Helene is one of four known Trojan moons, so called because it orbits at a Lagrange point. A Lagrange point is a gravitationally stable position near two massive bodies, in this case Saturn and larger moon Dione. In fact, irregularly shaped ( about 36 by 32 by 30 kilometres) Helene orbits at Dione's leading Lagrange point while brotherly ice moon Polydeuces follows at Dione's trailing Lagrange point. The sharp stereo anaglyph was constructed from two Cassini images (N00172886, N00172892) captured during the recent close flyby. It shows part of the Saturn-facing hemisphere of Helene mottled with craters and gully-like features.

Technorati Claim Code: 9CN8HGUDKM3X
Tomorrow's picture: below the plough


< | Archive | Index | Search | Calendar | RSS | Education | About APOD | Discuss | >

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
NASA Web Privacy Policy and Important Notices
A service of: ASD at NASA / GSFC
& Michigan Tech. U.