On 24 December 1968, one of the first images of the Earth was taken. Fifty years later, reanalysis allows us to rebuild the atmospheric conditions on that photo.
By Jose Prieto (EUMETSAT)
Half a century after the iconic Earthrise photo taken from Apollo-8 in orbit around the Moon, a reconstruction of the weather situation is provided by ECMWF. The ECMWF ERA-40 project has combined available weather information from 24 December 1968, with a model assimilation scheme to show the cloud situation on any date from 1957.
The projection used for showing the cloud on Figure 1 (left hand side) is that of Meteosat at 0°. Meteosat does not show latitudes above 80°, however, these latitudes are visible from the Moon. Therefore, the Meteosat image is more reduced in geographical scope than the Earthrise image.
The idea of an Earthrise, applies only to orbits around the Moon. Standing on the lunar surface at the near side, the Earth is at a fixed spot above the horizon, while the Earth rotates, and the weather on it changes.
Despite the difference in points of view (Apollo was 10 times further away than Meteosat and ca. 20° to the West) it is easy to compare locations on the surface:
- Frontal structures north west off the coast of Africa (A), which is well defined in the model reanalysis.
- Clear area around Namibia (B)
- Unusual cloud over Niger and Chad (C) is however missing in the model, perhaps due to data scarcity in the African region.
- Fronts centred on the Southern Atlantic (D).
ERA-40 assimilates surface pressure data out of different meteorological sources from 1957. Although the high levels of the troposphere were less reliably described those days than today, this chart from the experiment also shows, for the north Atlantic, a good agreement between Earthrise features and the 925 HPa isolines.
It is impressive that only in recent times, and with the support of evolved numerical models, it has been possible to retrieve the meteorology of the Apollo-8 image taken by lunar module pilot Bill Anders during the first manned voyage around the moon, when the meteorological observational network, on the ground and in the low atmosphere, was rudimentary, compared with today's network.
According to NASA, it's first Earthrise image was actually taken by the Lunar Orbiter 1 spacecraft in 1966. But the Apollo mission image is, perhaps, the most iconic. On Christmas Eve evening 1968, the astronauts — Commander Frank Borman, Command Module Pilot Jim Lovell, and Bill Anders — held a live broadcast from lunar orbit, in which they showed pictures of the Earth and moon as seen from their spacecraft. At the time Lovell said: "The vast loneliness is awe-inspiring and it makes you realize just what you have back there on Earth."
From 1975 things changed and different views of Earth became possible, as the GOES series started cover part of the planet from the geostationary orbit. Although used as a projection reference in this short study, the Meteosat satellites have only been in orbit since November 1977, and provide no information for the cloud retrieval presented here.
A more recent Earthrise picture is shown in Figure 2, which compares an image from the Lunar Renaissance Orbiter (LRO), a NASA robotic spacecraft currently orbiting the Moon, on 12 October 2015 with Meteosat-10 Natural Colour RGB. Again, the view from the imager in the Moon's neighbourhood captures a larger fraction of the Earth surface than the Meteosat satellite.
The ERA-40 re-analysis (Royal Meteorological Society)