B How Can Astronomy Even Occur? (Oort Cloud)

[sophiecentaur]

It just struck me that we are as likely to be aware of Oort objects between us and stars behind them due to shadowing as we are to see them due to them being illuminated by stars that are behind us - or even the Sun (the most likely candidate). We do not see Oort objects, as far as I know and their presence has not been inferred by any shadowing effect either. We only infer the presence of the clouds because of objects that appear occasionally, much nearer (comets).

 

[Jenab2]

When an incoming comet has an elliptical orbit, it is possible to find the orbit's semimajor axis from the comet's observed speed and heliocentric distance, using the Vis Viva equation, which is essentially an expression of the conservation of energy in a gravity-dominated physical system. Then with the polar equation of the ellipse, pole at the sun, you can get the eccentricity of the comet's orbit, though this is most easily done when the comet passes through its perihelion. With the semimajor axis and eccentricity both known, you can calculate the aphelion distance.

 

[sophiecentaur]

When an incoming comet has an elliptical orbit, it is possible to find the orbit's semimajor axis from the comet's observed speed and heliocentric distance, using the Vis Viva equation, which is essentially an expression of the conservation of energy in a gravity-dominated physical system. Then with the polar equation of the ellipse, pole at the sun, you can get the eccentricity of the comet's orbit, though this is most easily done when the comet passes through its perihelion. With the semimajor axis and eccentricity both known, you can calculate the aphelion distance.

I'm not sure what that has to do with the visibility of Oort objects?

 

[Jenab2]

I'm not sure what that has to do with the visibility of Oort objects?

You don't need to see Oort Cloud objects to know that they're there. You only need to compile statistics on the original distances (now aphelion distances) from which comets come. Then you know how far away the Oort Cloud is. This doesn't work with old comets, because old comets might have brushed by objects in the inner solar system and had their aphelions reduced. But it ought to work for young comets just fine.

 

[rootone]

The Oort cloud is not packed full of objects and for that matter the much nearer asteroid belt of the inner solar system is not,
There are enough objects to make a distinct feature, but nothing like the worst cases of pop-sci presentations with hundreds of kilometer sized objects constantly colliding.

 

[sophiecentaur]

You don't need to see Oort Cloud objects to know that they're there. You only need to compile statistics on the original distances (now aphelion distances) from which comets come. Then you know how far away the Oort Cloud is. This doesn't work with old comets, because old comets might have brushed by objects in the inner solar system and had their aphelions reduced. But it ought to work for young comets just fine.

Oh yes. I realize that we can deduce the presence of the Oort Cloud but we can't actually 'see it'. That's pretty a pretty normal situation in Science.