How big and bright is the Sun seen from 120 AU?

[beginner49]

Hi all

Currently, Voyager 1 is about 120 AU from the Sun. I wonder how big (or small) and bright would the Sun be seen from aboard this spacecraft . What approximate magnitude?.

Thanks in advance.

 

[BadBrain]

Hi all

Currently, Voyager 1 is about 120 AU from the Sun. I wonder how big (or small) and bright would the Sun be seen from aboard this spacecraft . What approximate magnitude?.

Thanks in advance.

Here, thanks to Caltech, is an artist's conception of the Sun from the vicinity of Sedna at 8 billion miles' (about 86 AU) distance:

 

[Chronos]

It's still very bright, even at 120 au, at about magnitude -16.3 [the full moon from Earth is about -12.7. So you would easily be able to read a newspaper. It would, however, be a virtual point source at that distance.

 

[beginner49]

BadBrain and Chronos

Thanks a lot for your replies. That of being able to read a newspaper is a very interesting detail.

thanks again.

 

[Feodalherren]

On a related topic, I heard that voyager was still accelerating, why? What causes it to accelerate further?

 

[Dickfore]

The angular size θ of the Sun's disk is given by the formula:
$$\sin \left( \frac{\theta}{2} \right) = \frac{R_S}{d}$$
where R_S is the radius of the Sun, and d is the distance from it.

Because the distance is much larger than the Sun's radius, the sine is very small. Therefore, to a sufficient precision we may substitute:
$$\sin \left( \frac{\theta}{2} \right) \approx \frac{\theta}{2}$$
provided that we measure the angle in radians. Nevertheless, we see that:
$$\theta \approx \frac{2 R_S}{d} \propto \frac{1}{d}$$
the angular size is approximately inversely proportional to the distance. At 1 A.U. (the Earth), the angular size of the Sun is about 31' (arc minutes). Therefore, at 120 A.U. it is:
$$\theta = \frac{31 '}{120} \times \frac{60 ''}{1 '} = 15.5 ''$$
that is about 15 arc seconds.