The Radio Telescope at Nançay France

An Astrofarm visit to the Nançay Radio Telescope

At the beginning of April we were fortunate enough to be able to visit the Nançay radio telescope which is located in the small French commune of Nançay, about two hours’ drive south of Paris and about 3 hours’ drive north from Astrofarm. The radio telescope is developing and operating among the biggest radio astronomy instruments in the world, observing the universe at wavelengths between 3 cm and 10 m.

What is a radio telescope?

A radio telescope is a receiver picking up sound and signals in different wavelengths. Our normal telescopes pick up light waves giving the observer an image. A radio telescope usually has similar features to a satellite dish and work on same principle as telescopes i.e the bigger the focal length (bigger the dish) the better the reception from fainter objects and those much further away.

The Nançay radio telescope

The station saw first light in 1965, after an inauguration by the then French president, Charles de Gaulle and is currently being jointly operated by The Paris Observatory (Observatoire de Paris), The National Research Council for Scientific Research (Centre National de Recherche Scientifique – CNRS), and by the University of Orléans. It is the world’s fifth largest radio-telescope and was Initially built for hydrogen gas observations, this instrument has been constantly improved since then. Today it observes galaxies, comets, star envelopes and it also times pulsars.

Large receiver Nancay Radio Telescope

The Nançay radio-telescope (NRT) is composed of an adjustable dish (200 m x 40 m) which reflects radio waves towards the fixed large dish (300 m x 35 m). This then sends those waves towards the focal chariot where they are collected and sent to specific receivers.

Radio telescope Nancay

At Nançay there is also the Kilometre Array (lots of smaller dishes spread over a large area). There are 47 dishes in a T shape which gives it a triangular reception area of 1 kilometre. It is known as “The Nançay Radio Heliograph”. There are 19 antennas on the East-West axis over a length of 3200 m and 25  antennas on the North-South axis over a length of 2400 m. It observes in a frequency range of 150 MHz to 450 MHz and can take images. Each antenna is motorised to follow the Sun for  7 hours a day. The collection of recorded signals allows building a radio image of the solar corona and solar eruptions.

Kilometre Array Nancay France

There is a very informative website for the radio telescope and the departments that are using them. Here you can also read about the history, collaboration and research being done currently at the site.

Andrew Davies

Our trip was intended as a research/network day we had planned the visit to coincide with one of their stargazing evenings run once a month. These events are staffed by members of the Paris Observatory and the local Nançay astronomy club. We went on the final session of the season as the stargazing evenings do not run over the summer months because it doesn’t get dark early enough.

The visitor centre

The visitor centre in itself, is well worth a visit and the in-house planetarium puts on a stunning show of the night sky and videos of our place in the universe (note: all events are presented in French only).

The website advertises all the events that they offer. It is worthwhile contacting them a day or so before you intend to visit to make sure it is open. The stargazing evenings are limited places and you will have to book a place in advance. The visitor centre exhibition has lots for you to see and some very interesting hands on displays.

There is only one small café machine/dispenser which dispenses the standard size French coffee and also a cold drink machine. Apart from that, there are no catering facilities onsite, so packed lunches are advisable.

If you intend to book a trip which coincides with a stargazing event, there are a few small cafes, bars and restaurants in the nearby village. You will have plenty of time to visit these as the stargazing doesn’t normally start until 8.00 pm.

Open times for the visitor centre are: 7 days a week from 9:30 am to 12:30 pm and from 1:30 pm to 5:30 pm. In July and August the site is open continuously from 9:30 am to 6:30 pm. Admission for the exhibition centre, planetarium show and the site tour is €9 for adults or €6 for just the exhibition centre.

The guided tour and stargazing evening

The guided walk round the station took about an hour and was in French. However; if you have some knowledge of radio astronomy, and basic French language, you can pick up the main points of the tour and the layout of the observatory is fairly self-explanatory. It may be worth inquiring if they do group visits in other languages as some of the staff spoke very good English. The evening stargazing was unstructured with a large group of local astronomers setting up their telescopes and being available to show people different objects. Despite the nearly full moon, the view of galaxies and a few small nebula was very good. We were also treated to a pass of the ISS over the top of the large telescope.

Circumpolar over Nancay radio telescope

Here is a link to some of the images we took while at the centre. The Paris Observatory (who are joint operators of Nançay radio telescope) saw my pictures on social media and were so impressed with them that they have asked for copies to use on the new publicity material for the 350th anniversary celebrations this year of the Paris Observatory! I am very flattered.



Combined with a planetarium show and guided tour of the station, Nançay radio telescope it is well worth a day out and great value for money. We easily filled a whole afternoon and evening and we learnt so much from the exhibition and the guided tour. The site is in a stunning rural location and there are some wonderful photographic opportunities around the radio telescopes – they are quite stunning to see!  We are already looking forward to a return visit in the autumn when the evening stargazing sessions resume for the season.