|
Imagine a giant sun, 25 times
the diameter of our Sun, and some 200 times greater luminosity, moving
so fast it may well have come from another galaxy. Arcturus - one of
the brightest stars in the sky, now high above the northern horizon -
is just that. It is sufficiently far away that what you see tonight is
Arcturus in the year 1969, for that is how long it takes its light to
reach Earth. Had it been somewhat closer, it would have completely
dominated our evening sky.
Higher still above Arcturus is
an object that appears brighter, but the light travel time is only 35
minutes. This is the planet Jupiter; equally a giant in the planetary
sense, for it is by far the largest in our Solar System and 11 times
the diameter of our Earth. A small telescope reveals its disc, and
even binoculars show the four large moons that orbit around it.
Planets Saturn (bright,
yellowish) and Mars (faint, reddish) are low in the western sky and
appear closest to one another on June 18.
The Moon is in the evening sky
until June 13 and from June 27.
|
