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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.

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

Logarithmic Spirals

Explanation: Uncomfortably close Typhoon Rammasun (right) and 25 million light-year distant galaxy M101 don't seem to have much in common. For starters, Rammasun was only a thousand kilometers or so across while M101 (aka the Pinwheel Galaxy) spans about 170,000 light-years, making them vastly dissimilar in scale, not to mention the different physical environments that control their formation and development . But they do look amazingly alike: each with arms exhibiting the shape of a simple and beautiful mathematical curve known as a logarithmic spiral , a spiral whose separation grows in a geometric way with increasing distance from the center. Also known as the equiangular spiral , growth spiral, and Bernoulli's spiral or spira mirabilis , this curve's rich properties have fascinated mathematicians since its discovery by 17th century philosopher Descartes . Intriguingly, this abstract shape is much more abundant in nature than suggested by the striking visual comparison above. For example, logarithmic spirals can also describe the tracks of subatomic particles in a bubble chamber , the arrangement of sunflower seeds and, of course, cauliflower .

Date May 17, 2008
Credit Image Credit: M101 - NASA , ESA , CFHT , NOAO ; Typhoon Rammasun - MODIS , NASA
Comparison: Lawrence Anderson-Huang ( Ritter Astrophysical Obs. , Univ. Toledo)
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
A service of: ASD at NASA / GSFC,
NASA Science Activation & Michigan Tech. U.