Naz

2016-Oct-23, 10:20 PM

I am doing an Introduction to Astrophysics course. We have just covered the Airy Disc and Diffraction problems.

I have a tutorial question which I don't understand. I have done the first part:

The EELT will have a mirror of diameter 39m. Calculate the best possible resolution if it observes at 500nm.

I get that to be 1.564 x 10^-8 radians which converts to 3.23 x 10^-3 arcseconds using the equation for the angular size of the Airy Disc:

Theta = 1.22 Lamda/Aperture

OK so far I think. Starightforward.

But then I am asked "Assume that the EELT uses a detector with square pixels, and the size of each pixel matches the resolution of the telescope, calculate the Flux received from Alpha Centauri by one pixel. I am told that Alpha Centauri B has a radius 0.86 of the Sun and is 1.3 pc away.

I can calculate the Flux at Earth from Alpha Centauri. What I don't know is how to relate the size of the pixel to the resolution of the telescope which I calculated to be 1.564 x 10^-8 radians. I am assuming that the pixel will have the dimensions of the Airy Disc. But how would I calculate that?

We haven't done focal lengths yet. I am thinking that maybe there is a geometrical solution where if I have the Mirror Diameter Size, and I have an angle, so if there's a focal length implied by the mirror size then that would allow me to calculate the Airy DIsc size and hence the pixel size and hence the Fkux received by each pixel?

Can anyone help?

Thank you

I have a tutorial question which I don't understand. I have done the first part:

The EELT will have a mirror of diameter 39m. Calculate the best possible resolution if it observes at 500nm.

I get that to be 1.564 x 10^-8 radians which converts to 3.23 x 10^-3 arcseconds using the equation for the angular size of the Airy Disc:

Theta = 1.22 Lamda/Aperture

OK so far I think. Starightforward.

But then I am asked "Assume that the EELT uses a detector with square pixels, and the size of each pixel matches the resolution of the telescope, calculate the Flux received from Alpha Centauri by one pixel. I am told that Alpha Centauri B has a radius 0.86 of the Sun and is 1.3 pc away.

I can calculate the Flux at Earth from Alpha Centauri. What I don't know is how to relate the size of the pixel to the resolution of the telescope which I calculated to be 1.564 x 10^-8 radians. I am assuming that the pixel will have the dimensions of the Airy Disc. But how would I calculate that?

We haven't done focal lengths yet. I am thinking that maybe there is a geometrical solution where if I have the Mirror Diameter Size, and I have an angle, so if there's a focal length implied by the mirror size then that would allow me to calculate the Airy DIsc size and hence the pixel size and hence the Fkux received by each pixel?

Can anyone help?

Thank you