ALMA captures the rotation of the large asteroid Juno

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The large ground-based telescope ALMA has captured a series of images of the large asteroid Juno, allowing scientists to estimate its rotation and overall shape.

Linked together into a brief animation, these high-resolution images show the asteroid rotating through space as it shines in millimeter-wavelength light. “In contrast to optical telescopes, which capture the reflected light from the Sun, the new ALMA images show the actual millimeter-wavelength light emitted by the asteroid,” said Todd Hunter, an astronomer with the National Radio Astronomy Observatory (NRAO) in Charlottesville, Va.

…The complete ALMA observation, which includes 10 separate images, documents about 60 percent of one rotation of the asteroid. It was conducted over the course of four hours on 19 October 2014 when Juno was approximately 295 million kilometers from Earth. In these images, the asteroid’s axis of rotation is tilted away from the Earth, revealing its southern hemisphere most prominently.


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