| From: Mark Senden | 21/10/99
11:48:53 |
| Subject: properties of reflected light | post id:
1422 |
| Hi Karl I've been thinking about this one for about 9 years; Why do stars twinkle and planets don't ? | |
| From: Martin B | 21/10/99
12:01:18 |
| Subject: re: properties of reflected light | post id:
1437 |
| In the atmosphere there are
pockets of air that are warmer than the surrounding air. These warm air
pockets move around. Because this air is warmer, light bends as it passes through the pocket. Light from both planets and stars is bent by warm air pockets. However the result is different. Stars are a long way away. The light that reaches Earth from these stars is almost perfectly parallel. When a parallel beam hits a warm air pocket between our eyes and the star, the bit of light that we would have seen (if the pocket was not there) bends away from our eyes, and we lose sight of the star. When the pocket moves, we regain sight of the star. This is what twinkling is. Planets are relatively close. The light that reaches Earth after reflecting off planets is not parallel. Instead it forms a cone of light in our atmosphere. When a ray of light from a planet bends away from our eyes, another bit of light going through the air pocket at a slightly different angle is bent towards our eye. We still see light from the planet so it doesn't twinkle. | |