Hi Philippe,

Denis has this right, but I should mention one small detail: set
the screen center close to the plane of the ecliptic, and _then_ hit
Ctrl-F5 and enter the desired distance.

You will then "back away" by that distance from your "normal" viewpoint.
Previously, for your view-from-above, you probably got the south ecliptic
pole (somewhere near RA=6, dec=-67) centered and hit Ctrl-F5. Some of this
is discussed at

http://www.projectpluto.com/useless.htm#Viewpoints

Alternatively, you can do as you originally suggested, setting a
viewpoint near the sun's equator and an altitude of, say, 1e+10 km.
I just tried this, and it worked, putting me ten billion km (about
67 AU) away from the Sun. There are two problems with this.

First, when I went back into the Location dialog, Guide showed
the altitude as 66.87 AU. When I clicked "OK", this got read back
in as 66.87 _meters_, the bug you noted. I'll fix this.

Second, a location of this sort will rotate with the sun. So
you'll zip around the solar system once a month or so. This can be
useful in some situations; you can, for example, put yourself 40000
km over the earth's equator to get the view from a geostationary
satellite. Or you can put yourself at one of the Earth-Moon Lagrangian
points (the Trojan points, or the places where one would "hover"
between the earth and moon or just over the far side of the moon).
This latter is discussed at

http://www.projectpluto.com/interest.htm#lagrange

-- Bill