Imaging the Far Side of the Sun

In 2000, Doug Braun and Charlie Lindsey used the technique of helioseismic holography to image, for the first time, active regions on the backsi... er, far surface of the Sun. The figure on the right (click for a high-resolution version) shows some examples of far-side seismic images obtained from MDI observations over a ten day period, and compares them with front-side magnetograms obtained two weeks later (as the regions moved into direct view). The approach exploits the horizontally extended acoustic travel-time reductions recently discovered in plages and moats surrounding sunspots. Large active regions are readily apparent in seismic images reconstructed using observations of global p-modes which can propagate long distances through the Sun without significant loss of coherence. The first images of the far side of the Sun were published in the March 10, 2000 issue of Science (reprint here) and reported in a ``Space Science Update'' at NASA Headquarters. Starting in the fall of 2000, Lindsey and Braun began a collaboration with Phil Scherrer and the SOI-MDI team to produce daily images of the solar far side. In April 2001, the web site was officially announced by NASA and ESA. Here is the most recent far-side image.

The initial images of the far side were limited to a region of the Sun within a heliocentric angle less than about 50 degrees from the antipode of disk center. In 2001, Braun and Lindsey demonstrated in this ApJ Letter how holographic procedures may be employed to produce diffraction limited images of the entire far surface (and poles) of the Sun as shown in the Figure to the left. The top four panels show composite images of the near-side magnetic flux density and far-side acoustic travel-time perturbations for four succesive days, and the bottom panel shows a synoptic magnetogram for the following solar rotation. Here is a nice mpeg, courtesy of Phil Scherrer, showing a sequence which compares full-hemisphere MDI farside images with the previous images.

During 2001, the newly upgraded GONG+ network began returning high resolution images. Using some of the first 24 hours of continuous data available, a comparison of far side images made from GONG+ and MDI was made (see figure to the right). The images are nearly identical, demonstrating the feasibility of continuous montioring of the solar far side using the GONG+ network. See the GONG farside imaging site for the daily image from GONG, as well as more information.

Below are links to some of the press releases and media coverage of far-side imaging as well as graphics and movies prepared for public dissemination. Note that most of the outdated links to the media coverage were removed.

Links to far-side imaging services and related items:

SOI-MDI far-side synoptic maps (now includes daily far-side image)

GONG farside imaging site

SWAN far side site (another interesting way to monitor the solar far side)

Links to press releases and media coverage:

Press release on first far-side image from GONG+

ESA release on initiation of routine far-side service

NASA's Space Science Update: press releases and graphics

SOHO Hot Shot

National Science Foundation's press release

MDI-SOI site at Stanford with links to more movies and media coverage

Most recent far-side image

For a list of relevant publications see Doug Braun's homepage


This research uses solar observations obtained primarily from the Solar Oscillations Investigations - Michelson Doppler Imager on SOHO and the Global Oscillations Network Group (GONG), and is funded by the National Science Foundation and the National Aeronautics and Space Administration.