This month of October 2023 is marked by the return of a well-known visitor: comet 103P Hartley. We tell you everything about this fascinating object visible since the end of September in the night sky.
Discovered in 1986, Comet Hartley 2, also called 103P Hartley, is a periodic comet that visits us approximately every 6.5 years. This year, the comet has been visible in the night sky since September. It will reach its closest point to the Sun this October 12 and can be observed from the northern hemisphere using a pair of binoculars or a telescope.
To see the comet, you will have to direct your gaze towards the constellation Gemini in which it is located. This emerges from the western horizon a little before midnight around mid-October and earlier and earlier in the evening as the days pass. To easily identify the Gemini constellation, you can use a sky map like the one offered on the Stelvision website or a mobile application like Sky Tonight (available on the App Store and on Google Play). The comet is therefore visible all night for amateur astronomers equipped with binoculars or a telescope.
A well-known so-called “hyperactive periodic” comet
In 2010, the Deep Impact probe designed by NASA went to meet this comet when it was close to Earth. The machine was thus able to fly over the object at a distance of only 700 kilometers, the opportunity to make a certain number of observations and take multiple measurements. We learned that Hartley is a so-called “hyperactive” comet, which means that its activity is much greater than what one would expect from a comet of this size. Its peanut-shaped core contains carbon dioxide which vaporizes under the effect of the heat, expelling the dust found on the surface of the comet. This mission also made it possible to obtain some spectacular photos of the comet revealing its astonishing shape and the jets of gas escaping from one of its ends.
The object of a participatory science experiment
Hartley’s passage is an opportunity for the French Astronomical Association (AFA) to propose a collaborative science campaign in which all volunteers are invited to participate. The objective of the project is to measure the increase then the decrease in brightness of the comet throughout its passage. All budding astronomers who wish can therefore bring their camera, telescope or telescope to photograph the bolide and measure its brightness. The AFA provides a tutorial which explains how to carry out this measurement and shares it on its site.
