Helio- and Asteroseismology


The orbit of SoHO

SoHO moves between the Sun and the Earth, in an orbit close to the so-called L1 point, where the force of gravity of the Sun and the Earth nearly cancel each other. This point is at a distance from the Earth of about 1.5 million km, which is about 4 times as far away as the Moon. The figure shows the complicated track that SoHO traced, before it approached its final orbit. The orbit has a number of advantages :

  • It allows us to study the Sun without interruptions.
  • The velocity of SoHO relative to the Sun is very low : This is an advantage for the Doppler observations of the velocity of matter on the solar surface.
  • SoHO is inside the solar wind, outside of the magnetosphere of the Earth. One of the purposes of SoHO is to measure the physical conditions in the solar wind undisturbed by the Earth's magnetosphere.
There is also a rather important disadvantage :
  • The large distance makes it difficult to transmit all the measurement results back to Earth. To get the full set of data back here we must use the American Deep Space Network, which is only fully available for 2 - 3 months every year.