Walking on the Moon – by telescope
We have all seen the images of the first manned Moon landing in 1969 often enough on the TV and remember the pictures of the lunar surface taken from orbit or from the landing site itself. But how much of all this can be seen with a telescope? And just where is the landing site? Here is a travel guide with a very special destination.
When Neil Armstrong and Buzz Aldrin landed on the Moon in July 1969, I was 13 years old and fascinated by the fuzzy black and white images on my television set. So much so, that I watched the landing site for hours on end with my first small telescope and dreamed of being part of this great space adventure. Sadly, even with the largest terrestrial telescopes, you cannot see the traces left by the astronauts on the lunar surface. This was achieved just recently for the first time by the high-resolution camera on the Lunar Reconaissance Orbiters. But it is exciting even to be able just to identify the area of the landing sites with your own telescope.
The lunar surface. (Download High-Resolution). Credit: Rolf Hempel.
On the morning of 31 July 2010, the conditions were favourable for a trip to 'Tranquillity Base', the landing site for the first astronauts. It was just before sunset there. Each surface detail was casting a long shadow, which makes them easy to recognise. I took the opportunity to make an image of the Moon from my garden in Buchholz (Westerwald) at 04:29.
My equipment is quite a lot better than the telescope I had 41 years ago. The objective lens is a three-element apochromat with a 130-millimetre aperture and 1200-millimetre focal length, fitted with a flat field corrector, which flattens the image area and increases the focal length to 3000 millimetres. The Moon almost completely fills the 22-megapixel full-format sensor of my digital single-lens reflex camera.
Mare Tranquilitatis in view
The approximate position of the landing site is marked with a small rectangle in this overview of the Moon, in the southwestern Mare Tranquillitatis, the Sea of Tranquillity. Now we use a greater enlargement to look for the landing site itself; simply enlarging the image is not sufficient, because the image noise becomes too strong. So I first overlaid ten individual images as precisely as possible and then enlarged the result. Since the 'noise pixels' in each image are in different positions, they disappear in the averaging process.
Here is the result: the photograph shows a lot of detail in the area of the landing site. The smallest visible craters have a diameter of two and a half kilometres. Despite this considerable size, they look like a one-euro coin at a distance of four kilometres when viewed from the Earth. This explains why we cannot see the actual footprints left by the astronauts.
This version of the image is marked with some interesting sites. First of all, the names of the three Apollo 11 astronauts. The International Astronomical Union named three small craters in the vicinity of the landing site after them, with diameters from 4.6 kilometres (Armstrong) to 2.4 kilometres (Collins). A bit south of the landing site you can see 'US Highway One'. The astronauts had to familiarise themselves with the area before the mission and gave some formations memorable names. This system of rills, officially called Rimae Hypathia, must have reminded them of the famous Californian coastal highway.
North of the landing site, we can see the 75-kilometre ghost crater Lamont, a system of 100-metre tall undulations in the ground of the otherwise flat terrain, which is only visible when the Sun is very low in the lunar sky. Due to deviations in lunar orbits, scientists identified a very dense formation under the surface at this point, referred to as a 'mascon'. The most plausible explanation is that a large impact crater at this point has later been almost completely filled with lava from the Mare Tranquillitatis.
Before the lunar landing, there was considerable controversy among scientists as to whether the craters were volcanic in origin, or due to impacts. In the end, the impact theory won the day. But there are signs of volcanic activity on the Moon. We can see two of them at the top left of the image in the form of swellings in the terrain, named Arago Alpha and Arago Beta. Lava has lifted the surface of the Sea here and formed these domes. However, they look higher than they actually are; although they are 20 kilometres across, they are only 100 metres high. You would hardly notice climbing them, they have an angle of just 1.4° – not very steep.
There are so many more things I could tell you about the big and small details in this image. But best of all is to look at the Moon yourself, through a telescope. If you're an early riser, the period just before the waning half moon is the best time in the autumn. It's nearly as fascinating as actually flying to the Moon – but not quite!
Rolf Hempel is leader of the DLR Simulation and Software Technology Department and an enthusiastic amateur astronomer.