APOD: 2022 April 3 - CMB Dipole: Speeding Through the Universe

Good evening, Rallypoint, and welcome to the April 3rd Astronomy Picture of the Day (APOD): "CMB Dipole: Speeding Through the Universe." CMB stands for 'cosmic microwave background.' You also can see the term CMBR (cosmic microwave background radiation); we are essentially talking about the same thing.

Microwaves are the name given to radiation in the electromagnetic spectrum between the infra-red and radio region, with wavelengths typically in the 1mm to 10cm range. Some specific wavelengths of microwaves can be used to cook; if you had a microwave telescope in your house, it could likely see your microwave oven when it was turned on. CMBR is called 'background' because it is detected regardless of any direction we look in the Universe. It also appears to be in thermal equilibrium. So what's that?

If the electromagnetic spectrum of a substance is in 'thermal equilibrium', physicists call that substance a 'blackbody.' They use that term to describe a substance that has settled down to a natural state. An average piece of hot, glowing ember from a fireplace, for example, is not in very good thermal equilibrium. The charcoal that remains is a bit closer, but it is possible to go further. CMB presents a better 'blackbody' electromagnetic spectrum in the microwave than anything scientists can produce.

Which brings us back to today's APOD. The Cosmic Background Explorer (COBE) satellite was launched in 1989 to take precise measurements of detectable electromagnetic radiation with wavelengths between 1 micrometer and 1 cm (0.39 in) over the whole celestial sphere. It is from the COBE dataset that today's APOD begins to take shape. We know the Earth rotates around the Sun, and the Sun rotates within the Milky Way. The Milky Way orbits what astronomers call the Local Group of Galaxies. CMBR measurements from COBE exhibit a doppler-type effect with compressed wavelengths in the direction of this motion (being blue-shifted, or hotter) and wavelengths increasing in the opposite direction (i.e. red-shifted, or cooler). Today's APOD is a representation of collected CMB data. As the APOD write-up indicates, these results were both unexpected and remain unexplained. Why are we moving so fast? What is 'out' there? (Hint: if today's APOD isn't enough of a mind bender, read up on something called 'The Great Attractor.')