The famous color photograph known as Earthrise, as well as a black-and-white image taken a minute earlier, document the moment when Earth was seen for the first time by human eyes from behind the Moon. They were taken on December 24, 1968 by the crew of Apollo 8, the first humans to leave low Earth orbit. The sight of a small, intensely blue Earth rising above the barren, gray horizon of the Moon was one of the few things that NASA and the crew of Apollo 8 had not thoroughly planned and rehearsed beforehand. As historian Robert Poole noted, this lack of preparation meant that the sight of Earth came with the force of a revelation, not just for the astronauts but for everyone on the ground. We came all this way to explore the Moon, Apollo 8 astronaut Bill Anders said, and the most important thing is that we discovered the Earth. Using the latest elevation data from Lunar Reconnaissance Orbiter, this visualization attempts to recreate what the astronauts saw. The virtual camera of the rendering software is put in the position of the Apollo 8 spacecraft at the time of the photographs, as the spacecraft emerged from its fourth pass behind the Moon. It shows a two-minute interval centered on 16 : 39 : 06 UT (10 : 39 a.m. Houston time) on December 24, 1968. This is around the time of AOS (acquisition of signal), the moment when radio contact is re-established after being lost on the far side of the Moon. The position and motion of the spacecraft are based on a state vector, a set of (x, y, z) position and (vx, vy, vz) velocity values, published in NASAs Apollo 8 Mission Report about a year after the flight. The animator translated these values, given in Moon-centered inertial coordinates for Besselian year 1969.0, into a modern coordinate system, then calculated an orbit. The spacecraft was 110 km (68 miles, 60 nautical miles) above the surface of the Moon at 11°S latitude. It flew from 119° to 113°E longitude, about a mile per second, during the two minutes covered by the animation. The position of the sun and the position and orientation of the Earth were also precisely determined. Because its based on these calculations, this visualization isnt merely pretty. It can be used to find out exactly when the photographs were taken, where the spacecraft was at the time, and what part of the lunar terrain is visible. The animation includes a clock overlay, and it pauses to overlay each of the photographs at points where the views match. Also provided here, possibly for the first time, is a map that accurately depicts the areas of the Moon that can be seen in the photographs. It should be noted that the astronauts themselves see these images with the lunar horizon vertical and the Moons surface on the right side. This turns the Earth so that north once again points upward, which seems most natural to them. But those of us who havent experienced their unique perspective tend to feel more comfortable with a horizontal horizon. When viewed from most of the Earths land masses, the Moon, and everything else in the sky, appears to rise sideways ! Completed: 04 April 2012 Animator: Ernie Wright (USRA) (Lead) Producer: Chris Smith (HTSI) Scientist: Richard Vondrak (NASA/GSFC) Platforms/Sensors/Data Sets: Terra/MODIS/Blue Marble (Jun to Sep 2001) Apollo 8 Trajectory Reconstruction (Dec 1968 to Nov 1969) Clementine/UVVIS Camera/750-nm Basemap (Feb 26 to Apr 21 1994) LRO/LOLA/Digital Elevation Map (Aug 2009 to Sep 2011) Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio
Posted on: Thu, 24 Oct 2013 12:32:37 +0000
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