37
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
F. Sánchez, The Rise of Astrophysics in Modern Spain, Astronomers’ Universe,
https://doi.org/10.1007/978-3-030-66426-8_5
5
The Zodiacal Light (1962–1982)
The zodiacal light can be seen from the Earth as a faint pyramid-shaped glow
centred on the ecliptic in early dawn or late dusk. It is caused by the scattering
of sunlight by tiny interplanetary dust grains in the Solar System. The spectacle of the roseate pyramid of the zodiacal light reaching almost to the zenith,
easily seen with the naked eye from the limpid Canarian summits (particularly in the spring and autumn months when the ecliptic is at its most perpendicular to the horizon), is at once beautiful and unsettling. This ‘false dawn’,
as the Arabs called it, is a little-known phenomenon to the public at large
because of the light contamination that drowns out this visual boon of nature.
The zodiacal light provided our first clue to the existence of the interplanetary medium and gets its name from being visible in the constellations of the
zodiac. The axis of this pyramid coincides closely with the invariable plane of
the Solar System (‘the maximum plane of Aries’, as Laplace dubbed it), which
forms an angle of one degree, thirty-six minutes of arc with the ecliptic. Given
the morphology of the zodiacal cloud and its nature, it is logical that it should
be symmetrical about the sun and be located in the same plane in which the
major planets describe their orbits. We may picture it as having a lenticular
shape, extending out to at least the orbit of Jupiter, with a central hole occupied by the sun.
Zodiacal dust may be considered simplistically as a remnant of the protoplanetary disc, the residual detritus of collisions among planetesimals of the
primordial nebula. How can it be possible that these clouds of primordial
electrically charged micro-grains, subjected as they are to significant electromagnetic forces that tend to disperse them, should remain stable over millions
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
F. Sánchez, The Rise of Astrophysics in Modern Spain, Astronomers’ Universe,
https://doi.org/10.1007/978-3-030-66426-8_5
5
The Zodiacal Light (1962–1982)
The zodiacal light can be seen from the Earth as a faint pyramid-shaped glow
centred on the ecliptic in early dawn or late dusk. It is caused by the scattering
of sunlight by tiny interplanetary dust grains in the Solar System. The spectacle of the roseate pyramid of the zodiacal light reaching almost to the zenith,
easily seen with the naked eye from the limpid Canarian summits (particularly in the spring and autumn months when the ecliptic is at its most perpendicular to the horizon), is at once beautiful and unsettling. This ‘false dawn’,
as the Arabs called it, is a little-known phenomenon to the public at large
because of the light contamination that drowns out this visual boon of nature.
The zodiacal light provided our first clue to the existence of the interplanetary medium and gets its name from being visible in the constellations of the
zodiac. The axis of this pyramid coincides closely with the invariable plane of
the Solar System (‘the maximum plane of Aries’, as Laplace dubbed it), which
forms an angle of one degree, thirty-six minutes of arc with the ecliptic. Given
the morphology of the zodiacal cloud and its nature, it is logical that it should
be symmetrical about the sun and be located in the same plane in which the
major planets describe their orbits. We may picture it as having a lenticular
shape, extending out to at least the orbit of Jupiter, with a central hole occupied by the sun.
Zodiacal dust may be considered simplistically as a remnant of the protoplanetary disc, the residual detritus of collisions among planetesimals of the
primordial nebula. How can it be possible that these clouds of primordial
electrically charged micro-grains, subjected as they are to significant electromagnetic forces that tend to disperse them, should remain stable over millions