| From: sharni | 16/12/99
14:37:00 |
| Subject: Planets Twinkle or Shine | post id:
17624 |
| My husband and I have regular
arguements about stars and planets twinkling and/or shining. I'm sure that
my Science teacher from high school said stars twinkle and planets shine -
due to reflected light - however they may appear to twinkle due to
atmospheric conditions. Who's right???? | |
| From: David Brennan | 16/12/99
15:21:14 |
| Subject: re: Planets Twinkle or Shine | post id:
17648 |
| Both stars and planets twinkle.
In most cases the apparent changes in brightness, or twinkling are caused
by the atmospheric distortions such as thermal affects and clouds, etc.
There are some stars whose light emissions vary which may cause a
twinkling effect, but most don't. The Hubble Telescope, for example,
doesn't see twinkling stars. Avoiding atmospheric distortions are one of
the main reasons that Hubble was put in orbit in the first place. Its also
why many observatories are in mountains, few atmospheric disturbances at
altitude (and I guess less atmosphere between you and the stars too
:) Cheers, David DAvid | |
| From: Daryn Voss | 16/12/99
20:57:22 |
| Subject: re: Planets Twinkle or Shine | post id:
17768 |
| If you go and take a look at
Jupiter about now, you will see it is not twinkling. The twinkling of stars and sometimes planets is due to fluctuations in the atmosphere (Earth's, that is.) While stars are very far away, and have an extremely small angular diameter in the sky. Planets have a much wider "footprint" in the sky, so the image is less likely to be affected by these fluctuations. Nonetheless, you can still see planets twinkling sometimes, especially if they are near the horizon. | |
| From: sharni | 17/12/99
11:19:14 |
| Subject: re: Planets Twinkle or Shine | post id:
17984 |
| If planets shine due to reflected
light whereas stars are emitting its own light, how can it be that both
planets and stars twinkle. Someone work out an argument so that planets
shine and stars twinkle or I'll lose my arguement with by
husband Sharni | |
| From: Daryn Voss (Avatar) | 17/12/99
13:03:32 |
| Subject: re: Planets Twinkle or Shine | post id:
18017 |
| The fact that planets reflect,
but stars emit their own light, has absolutely nothing to do with the
twinkle/non-twinkle problem. As far as appearances on earth are concerned (when looking up in the night's sky), the difference between stars and planets is that stars have a very small angular diameter in the sky. When I say small, I mean less than a millionth of a degree. The image of the stars will be very susceptible to interference from fluctuations in the earth's atmosphere. Planets are smaller than stars, but they are much, much closer. They have an angular diameter of about one hundredth of a degree. (This varies, of course.) If one small part of the image is distrubed by a fluctuation, it won't matter much becuase the rest of the image will remain. The "average" picture will be pretty clear. As I noted before, planets can sometimes look a bit twinkly, especially if they are near to the horizon, but it is this difference in angular diameter that makes them more impervious to the twinkle factor. As someone else noted before, it has nothing to do with anything the bodies themselves are doing. In space, stars don't twinkle. I don't know whether this lets you win your argument, but good luck! 8^) | |