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.

	本作品由NASA創作，屬於公有領域。根據NASA的版權政策：“NASA的創作除非另有聲明否則不受版權保護。”（參見：Template:PD-USGov/zh，NASA版權政策或JPL圖像使用政策）
	警告: 使用NASA的logo，徽標等受到美國法律14 CFR 1221的限制。 NASA網站還提供大量來自蘇聯/俄羅斯航天機構，以及其他非美國的太空機構的圖像。這些圖像不一定屬於公有領域。 根據哈勃空間望遠鏡的數據制作的素材，如果不是明確聲明由STScI提供，則可能受到版權保護。[3] 參看{{PD-Hubble}}和{{Cc-Hubble}}或{{Spacetelescope.org}}。 SOHO (ESA & NASA)聯合項目的探測器所創作的所有內容受到著作權保護，並且進行非教育性質的商業應用需要授權。[4] 每日一天文圖（APOD）網站的特色圖片可能受到著作權保護。[5]

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