File:Phobos shadow.jpg

Credit: NASA/JPL/Malin Space Science Systems [1] archive copy at the Wayback Machine [2]

The penumbral shadow of Phobos is visible on the landscape of Mars, as photographed by the Mars Global Surveyor. The center of the shadow was at approximately 10.9°N 49.2°W (Map of area archive copy at the Wayback Machine Map zoom archive copy at the Wayback Machine) at 04:00:33.3 UTC Earth time.

The image shows western Xanthe Terra on August 26 1999 at about 2:41 p.m. local solar time on Mars. The image covers an area about 250 kilometers across and is illuminated from the left. The dark spots on the crater floors are probably dark sand dunes. None of the craters pictured currently have names. Nanedi Valles is the meandering valley at the bottom right. The picture covers about 7°–15°N vertically and 52°–48°W horizontally. The vertical orientation of the image is 3.01° to the west of north; a north-pointing arrow superimposed on the image would point slightly to the right.

To determine the time of the shadow, we can look up the original image files at M04-03241 archive copy at the Wayback Machine (red) and M04-03242 archive copy at the Wayback Machine (blue). The "image start time" was 03:26:13.01 UTC, the "line integration time" is 80.4800 milliseconds, and the "downtrack summing" factor is 4. Since the shadow is centered at 6400 pixels from the bottom of the original 10800-pixel-high image (Mars Global Surveyor had a south-to-north sun-synchronous orbit), we add (6400 * 0.08048 * 4) = 2060.3 seconds = 34 minutes 20.3 seconds to get a time of 04:00:33.3 UTC for the center of the shadow.

	本文件完全由NASA创作，在美国属于公有领域。根据NASA的版权方针，NASA的材料除非另有声明否则不受版权保护。（参见Template:PD-USGov/zh、NASA版权方针页面或JPL图片使用方针。）
	警告: 使用NASA的标志、徽章、徽标等受到美国法律14 CFR 1221的限制。 NASA网站大量存储来自苏联或俄罗斯航天机构的图片，以及其他非美国的航天机构图片。这些文件不一定属于公有领域。 根据哈勃空间望远镜的数据制作的材料，如果不是明确声明由STScI提供，则可能受到版权保护。[3]参见{{PD-Hubble}}和{{Cc-Hubble}}。 SOHO（ESA和NASA）联合项目表示，由旗下的探测器创作的材料受版权保护，且对于商业性非教育目使用材料需要授权。[4] 每日一天文图（APOD）网站上展示的图片可能受到版权保护。[5] 国家太空科学数据中心（NSSDC）网站据信存储了受版权保护内容。其图库常见问答表明除非另有声明，图库的所有图片都属于公有领域。

External links

• NASA press release (November 1 1999)
• MOC Wide-Angle Images, Region Lunae Palus, Subphase M04 archive copy at the Wayback Machine
• Mars Global Surveyor Mars Orbiter Camera Image Gallery