Eclipse of the Radio Sun
Joachim Köppen Kiel Sep 2017
Some brief explanations
This simulation shows how the radio flux from the Sun changes during an eclipse
by the Moon. The Sun's radio emission comes from three contributions:
- solar photosphere: is modelled by a disc with a radius of one solar radius,
which serves as a unit of length. The disc has the specified brightness
(which is in units of the brightness of the shell source).
- Shell: the emission from chromosphere and corona is concentrated at the
solar limb ("limb brightning"), which makes the rim brighter than the middle
of the solar disc. It is described by its inner and outer radii, and the brightness
which is taken to be constant as 1.0 (shown as bright red).
- Spot: any active regions on the Sun show up as bright spots on the disk or
on the rim. The tool allows to place a single spot of given radius and brightness
at any position on the disc.
The image on the left displays the motion of the Moon across the face of the
still-standing Sun. The path of the Moon across the solar face is described
by the offset in vertical direction and the angle with respect to the horizontal
direction, to allow simulation of total and partial eclipses. Also, one can take into
account that the Moon's diameter differs from that of the Sun, and to deal with
annular eclipses. The blue circle indicates the half-power radius of the antenna
beam, which has a gaussian profile.
The plot on the right shows how the fraction of the radio flux changes with time,
i.e. the position offset of the Moon. Since the faster Moon overtakes the Sun in its
travel on the sky towards the East, the Moon moves from left to right in the image,
but the curve starts from the left hand side.
Vertical magenta lines mark the first and last contact of the optical eclipse.
The controls are:
- run once: the simulation is done rapidly once.
- stop: halts the simulation.
- run continuously: the simulation is done repetitively and more slowly.
- Mouse position: displays the coordinates of the present position of the
mouse in the plot.