Deze website in het Nederlands bekijkenSite en français

Venus transit

Why are scientists interested?

The 5 first observations of the transit of Venus, in 1639, 1761, 1769, 1874 and 1882 were used to determine the distance between the Earth and the Sun.

Famous astronomers, such as Cassini the first (1625-1712), Abbott Jean Picard (1620-1682), Jean Richer (1630-1696) and even Sir Edmond Halley (1656-1742) and later Joseph-Nicolas Delisle (1688-1768) refined the trigonometric method, called parallax.

However, the first measures of parallax, made using transits, were marred by an error due to an optical effect called the 'Black Drop effect'.

Since the Sixties, distance measurements using radar, as well as space probes, have allowed us to determine the size of our solar system far more accurately. This is when scientists came up with a new idea: Why not use the transit of Venus as a reference in the study of exoplanets?

There are many methods to detect exoplanets, which we will come back to later. One of these is called the "transit method". This method requires the observation of a possible transit. If a transit occurs, the apparent luminosity of the star reduces slightly (because a tiny fraction of its emitting surface is temporarily hidden). This method gives information on the mass, size and orbit of the planet.

Crédit: D. Ehrenreich - "Venus as a transiting exoplanet" - 3rd Europlanet strategic workshop - 4th PHC/Sakura meeting - 5-7 March 2012, Paris.


Studying this transit will allow scientists to see if such measurements would allow them to answer fundament

  • Can we detect the atmosphere of an exoplanet of a similar size to the Earth (venus and the Earth are almost the same size)?
  • What molecular signatures are our instruments capable of detecting/measuring in the atmosphere?
  • Is this planet habitable? (Do we detect the molecules necessary for life?)


If you have any questions, click here.


Link naar de website van het Federaal Wetenschapsbeleid
Link naar de Federale Portaalsite