|With the every year by 4 cm increasing distance Earth-Moon in mind,
it is quite clear, that millions ago the moon every time, when it shadowed
Earth from Sun also covered large parts or very early all of the visible
corona from the Sun. In the opposite in the mid-range future in terms of
our planetary system, the apparent diameter of our moon will decrease,
so that no total, but only annular solar eclipses are then possible anymore.
And of course the remaining part of Suns disk will increase at these events
in the farer future even more...
So it's timely just by chance, that we can today witness solar and annular eclipses and that the total ones nearly exactly cover the entire solar photosphere, enabling best view of the Suns corona.
One may ask, if there are other planet/natural satellite arrangements (today) in our solar system, which would enable such observations. This question is tackled by the following table, the round up follows below it.
Remarks: because the planets exceed in all relevant cases the satellites with respect of diameter so much, that they are clearly covering the Sun seen from their satellites, I don't consider these moon eclipsing events by their parent planets. Otherwise I ignore first, that the Jovian planets don't feature rigid surfaces or transparent atmospheres, but I treat them as somebody would float with a balloon or somewhat similar above the cloud deck. And finally the planetoids are also ignored, despite there are some cases like Idas moon Dactyl, from which we have knowledge of, partly because their high number and partly because of the extremely incomplete record of them...
The designations are: ' abbreviates for arc minutes, in which the apparent diameters of the celestial bodies are given; a C means total covering of Sun and corona, a T a total eclipse, the moon not more than by a factor two exceeding the Suns diameter, an A an annular eclipse, a moon diameter not less than half the Suns diameter and a P for lower coverages of the Suns disk. Keep in mind, that Mercury and Venus lack natural satellites and let me handle Pluto still as a planet, even some experts deny him today this status.
|parent planet||app. solar diameter||natural satellite(s)||apparent diameter|
others: tiny app.
others: tiny app.
others: too big
or too tiny (outer)
resp. only P
|Neptune||1.05'-1.07'||others: too big
|Now you can easily see, that the often heard respective read statement, that our moon is the only natural satellite with an apparent diameter comparable to the Sun seen from the parent planet, holds only true in a very narrowed fashion: this is correct, if one requests the ocurrence of total and annular solar eclipses. More generally, Jupiters Callisto creates total eclipses, which allow sight of the outer corona of the Sun (but only partly the inner), Jupiters Amalthea in its ragged shape creates interesting annular eclipses; due to uncertain sizes of Janus and Epimetheus, also not globular bodies, maybe, but not sure, even create both annular and total eclipses, and finally Uranus' satellites Cordelia and Ophelia create total eclipses with visibility of the inner corona, sometimes only slightly bigger in size than our sun. In rare cases, near the periapsis on its orbit, Nereid creates also annular eclipses of considerable size.|
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