Luna 2, like Luna 1, took a direct path to the Moon with a journey time of around 36 hours. This was dictated by the fact that the Earth-Moon gravitational system forced it to follow a curved trajectory, and launch had to occur from the side of the Earth opposite the Moon. Its journey time had to be, therefore, 12 hours, 36 hours or 60 hours in order to ensure that the Moon was above the horizon in the Soviet Union.

It is seen in the photograph on the right attached to the final stage of it launching rocket - a variant of the Vostok rocket which was later to send Yuri Gagarin into orbit around the Earth. The magnetometer boom is pointing towards the left.

Luna 2 hit the Moon about 800 kilometres from the centre of the visible disk 1959 September 13 at 21:02:24 (September 14 at 00:02:24 in Moscow).

On impact, it scattered a quantity of Soviet emblems and ribbons across the lunar surface. They were assembled into spheres which broke up on hitting the surface. About 30 minutes later, the final stage of Luna 3's launching rocket made its own crater on the Moon.

In order to measure the trajectory, Luna 2 and its final stage rocket which accompanied it to the Moon, were equipped with radio transmitters so that Earth-based receivers could measure the trajectory using the Doppler effect. Both Luna 1 and Luna 2 were also tracked using optical telescopes. To make things easier, both launching rockets released clouds of sodium gas which glowed under the influence of the Sun's radiation (similar to a gas discharge lamp). Luna 2's sodium discharge - achieved by exploding a thermite charge, which had been mixed with sodium metal. This occurred at a distance of 113,000 kilometres from the Earth. The cloud expanded at a rate of 1 kilometre per second, attaining a diameter of 400 kilometres before it became too faint to observe.

Successful optical observation called for an increase in the rocket's radiance artificially for at least a short period of time. Soviet astrophysicists suggested the artificial comet method to solve the problem in a most efficient way.

It will be recalled that comets owe their radiance to resonance dispersion when molecules and atoms intensely scatter incident light of some wave-lengths.

The astrophysicists figured that sodium vapours would be the best possible dispersing medium, as several pounds of sodium could give out a cloud visible several hundred miles way and have a radiance several hundred thousand times that of a space rocket.

Released from a rocket, sodium vapours would form a cloud around it which could be easily observed and by which it would not be difficult to determine the rocket's co-ordinates.

It required extensive experimental work to put this idea into practice. it is no easy task to have sodium evaporate in outer space without great loss. A special evaporator, therefore, was built in which sodium was mixed with Thermite and set on fire at the desired moment by an electronic programme-control device.

A suitable optical system was developed to observe the sodium cloud - the artificial comet. The requisite instruments were built by the optical industry within a short period of time.

The system included, on the one band, twin cameras with interference light filters to take pictures of the sodium cloud and, on the other hand, electronic telescopes to observe the sodium cloud with the eye and also to photograph it at exposures about one-hundredth of that of the twin cameras.

Such electronic telescopes convert a light image into an electronic one which is amplified and reconverted into a light image to be seen by the observer or recorded on a picture plate.

The artificial comet was fired by the second Soviet space rocket at 21 hours 39 minutes 42 seconds, September 12th (Moscow Time). it appeared as a dot with a rapidly increasing luminescence untfl it reached its maximum (fourth or fifth) stellar magnitude. Then the dot began to grow blurred, became a spot and then a blurred ring. At the end the cloud had a diameter of about 650 kilometres.

The rate of expansion was almost one kilometre per second. Photographic observation of the artificial comet, combined with radio methods, made it possible to determine to a high degree of accuracy the bearings of the rocket and to elaborate the further flight path to the Moon.