Ceres was the first minor planet to be discovered in 1802 and followed the prediction by the Titus-Bode's law that a body should exist at about 2.8 Astronomical Units from the Sun. But instead of a single planet at this distance, this part of space is occupied by the Asteroid Belt containing a considerable number of objects from Ceres which is 1003 km in diameter down to mere lumps of rock. The total mass of all the minor planets is estimated to be a minute fraction of the mass of the earth. This indicates that the asteroids were not the result of the break-up of a single planet as was once thought but rather the collisional debris of small bodies that condensed between Mars and Jupiter during the formation of the Solar System.

Not all asteroids occupy the space between Mars and Jupiter. One of them discovered on the 13th of August 1898 and named Eros after the God of Love orbits the Sun at a distance of 1.13 to 1.78 AU. Since the Earth is exactly 1 Au from the Sun this means that it can come pretty close. In fact in 1975 it came to within 23 million km - almost a lovers embrace ! (Probably more like the kiss of death !!)

The picture shown here was taken on the 13th of this month - August - a hundred years after its discovery. It shows the path of Eros, as in time-lapse photography, against the background of stars as it moves through space. This was made by superimposing five separate images taken at half-hour intervals. Eros is captured moving from right to left starting near the middle right of the page as a string of equally spaced dots each being Eros at a specific time. Imaging was started at 7pm and continued until the asteroid went behind a large Pine tree on the Western boundary. Unfortunately the first two images were not centred correctly so were abandoned which left the five shown.

Eros has an oblong shape measuring 7 by 16 by 35 km and has a rotation period of 5.3 hours. Seeing this I wondered whether the images showed this so did some comparative photometry. Sure enough there was a marked change in brightness over the 2 hours that the series covered. This is shown in the table below :-

North is UP

So the brightness of Eros changed just over half a magnitude while that of the check star varied by 3 hundredths
of a magnitude which indicates the uncertainty of the relative measurements but not any systematic errors.

For those interested in the technical details, a home built Cook Book CCD camera with a Johnson V filter coupled to a 300 mm F6 Newtonian was used. The V filter introduces a fair loss in overall sensitivity but even so the faint star nearest the first snap of Eros was measured at 16.9.

Acknowledgements: Danie Overbeek for drawing my attention to the event.