A Radio Telescope on the Moon

One of the most interesting radio frequencies for radio telescopes is that emitted by hydrogen atoms when excited by an energy input. Upon returning to its ground state, the atom emits a photon with a frequency of 1.42 gigahertz. This frequency corresponds to the microwave region, which ranges from 300 MHz to 300 GHz. If we focus a radio telescope on a cloud of gas and dust in our galaxy, which is composed mostly of hydrogen, this frequency is easy to detect.

But what happens if we try to detect this frequency in very distant regions of the universe? The expansion of the universe affects these waves by lengthening them (that is, decreasing their frequency), in the same way as the frequency of the cosmic microwave background radiation, which was initially in the visible and infrared regions of the spectrum, is now in the microwave region, with its peak at a frequency of 160.2 GHz.

Anniversaries of space exploration

Armstrong, Collins & Aldrin - Photo NASA

Fifty years after the arrival of man on the Moon, a couple of European sexagenarians remember the first landing:

“Do you know what day is today?”

“Saturday, why?”

“I mean the date.”

“July 20th 2019, what about it?”

“Exactly fifty years ago, man reached the Moon.”

“Oh yeah! But wait, there is something wrong here, didn’t they arrive on the twenty-first?”

"No, it was the twentieth, but it took them over six hours to get down from the capsule. By then, in Europe it was the twenty-first, but in the United States it was still the twentieth.”

“True! I remember it well. I saw it on TV. I was ten years old.”

“Me too.”