Wednesday, February 25, 2009

JAXA releases time-lapse of Reverse-Penumbra

The Japan Aerospace Exploration Agency (JAXA) and the Japan Broadcasting Corporation (NHK) successfully took moving images of the precise Earth rise moment when the Earth looked like a diamond ring using the onboard high definition camera (HDTV) of the lunar explorer "KAGUYA" (SELENE) on February 10, 2009 (Japan Standard Time, all the following dates and times are Japan Standard Time.)

The moment came when a penumbral lunar eclipse occurred and sunlight was covered by the Earth. During that time, since the view of the Sun from the KAGUYA was mostly covered by the Earth, the KAGUYA observed that the Earth looked like a diamond ring. This is the first time that this phenomenon was shot from the Moon.

The images were shot by the HDTV onboard the KAGUYA for space-use developing by NHK. The moving images were received at JAXA and processed at NHK.

* A penumbral lunar eclipse is a phenomenon in which the Sun, Earth and Moon line up in tandem, hence the Moon is in the Earth's penumbra, or, when you look from the Moon, the Sun is partially covered by the Earth (partial eclipse.) During this phenomenon, the volume of sunlight to the Moon decreases, and the Moon's surface looks darker when you look at the Moon from the Earth. The KAGUYA, which circles around the Moon on its polar orbit, can witness this phenomenon only twice a year at most, thus it was very valuable to capture the moving images of the phenomenon from the KAGUYA.

The Earth by the HDTV (Tele-camera) during the penumbral lunar eclipse (480x270px)

Figure 1 Image of the Earth by the HDTV (Tele-camera) during the penumbral lunar eclipse

This still image was a cutout from the moving images taken by the onboard HDTV (tele-camera) of the KAGUYA (SELENE) on February 10, 2009.

The bright part on the lower right side is the Sun and the black area surrounded by the thin light ring is the Earth. The red dotted line shows the Moon's surface. Most of the Sun is covered by the Earth and the Moon's surface.

The contour of the Earth is shining in a ring shape because of the atmosphere. It scatters in the atmosphere in the periphery of the Earth, and a part of the sunlight reaches the Moon. The Earth's rim looks like a blue ring from the Moon since it is thought that the scattering sunlight with blue color light occurs easily because of the Earth's atmosphere.

Figure 2 Sequence images of the Earth by the HDTV (Tele-camera) during the penumbral lunar eclipse

The KAGUYA captured the moving image of the Earth and the Sun gradually rising from the Moon's surface. The above sequence of images is a cutout from the moving image to show the rising process. The image on the far left is just after the Earth rise from the Moon's surface. It took about 47 seconds to film from the left to the right when the Sun came out from the Moon's surface and the diamond ring appeared.

Figure 3 Positions of the KAGUYA, Moon, Earth and Sun when images of the Earth-rise during the penumbral lunar eclipse

Public Affairs Department, Japan Aerospace Exploration Agency (JAXA)

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