NASA's STEREO-A Spacecraft Passes By Earth For The First Time In 17 Years #space #astronomy

On October 25, 2006, the Solar Terrestrial Relations Observatory (STEREO) mission was put into motion with the aim of observing the transfer of matter and energy from the Sun to Earth. Two spacecraft, STEREO-A and STEREO-B, were used to launch the STEREO mission. STEREO-A and STEREO-B were both launched onto Sun-orbiting trajectories (STEREO's Routes to Solar Orbits), with STEREO-A going ahead of Earth and STEREO-B moving behind it.

The STEREO-A spacecraft, which is still in use (STEREO-B went down in October 2014), will pass Earth for the first time since its launch 17 years ago in the middle of August 2023. STEREO-A is moving somewhat faster than Earth around the Sun, similar to racing vehicles travelling at various speeds around a circular track. After launch, STEREO-A began to distance itself from Earth and grew that distance with each orbit. Now that STEREO-A has completed 18 orbits about the Sun but Earth only completed 17, STEREO-A's lead is so enormous that it is approaching Earth from behind and is poised to "lap" it.

An illustration of STEREO-A's orbit as it passes Earth from mid-June 2023 to mid-October 2023. The Earth and Sun look stationary because the camera is locked to the Earth-Sun line, while the distant stars seem to be rotating around the camera. A broad shot of the inner solar system with STEREO-A and Earth indicated opens this film. The Solar Dynamics Observatory (SDO), the heliophysics missions circling the L1 Lagrange Point (the green cross), and the Moon's orbit are then visible when the camera zooms in for a closer look at Earth.

Credit: NASA's Scientific Visualization Studio