The Event Horizon Telescope (EHT) recently observed the shadow of M 87* (the supermassive black hole, of about 6 billion solar masses, at the center of the giant elliptical galaxy M87, which is about 55 Mly away). If the observations were made at the radio wavelength of 1.3 mm & were at the diffraction limit for angular resolution at about 50 micro-arcseconds, about what was the distance between EHT’s component telescopes?

i think it’s a. this is because if they measured the mass of something with a mass of 150g, then their final answer would have to be approximately 150g. though all of their answers are almost 150, rosa and tran have the closest answers (or the exact answer) to the accurate one.

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.

close lines strong magnet less close weaker

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.