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Life on earth depends on the sun. Day after day we see its
light and feel its {{U}} (36) {{/U}}, but we do not often know or
{{U}} (37) {{/U}} the birth or the beginning of their {{U}} (38)
{{/U}}. Yet there are amount of {{U}} (39) {{/U}} things about the
sun. One is its distance from the earth. This is about ninety-three
{{U}} (40) {{/U}} miles. It is to us, a long distance. A {{U}} (41)
{{/U}} of this distance, even if it could be made, would take {{U}} (42)
{{/U}} hundred years even in the {{U}} (43) {{/U}} rocket.
The sun makes us feel heat, even at a distance of ninety-three million
miles. This is not surprising. {{U}} (44) {{/U}}. But we receive only a
small part of this heat. The total heat of the sun could melt a column of ice
two and a quarter miles thick and ninety-three million miles high in one
second.
The brightness of the sun is equally astonishing. As we
said earlier, we receive only a very small part of t