First of all, in case you didn’t know, according to a few sources, today is not just Valentine’s day, but also:
Impotence Day, Condom day, Singles Awareness Day, Ferris Wheel Day, Congenital Heart Disease Day, and Pet Theft Awareness Day.
And on to the Astronomy! A classic favourite would be the Heart Nebula.
Located 7,500 light years away in the constellation Cassiopeia, this heart-shaped HII emission nebula is located along the plane of the Milky Way galaxy. HII regions like this one are used to probe the massive star formation in a galaxy. This is because massive O and B type stars emit a lot more ultraviolet radiation, which ionizes the molecular Hydrogen in their birth cloud. As one moves away from the star, the UV flux decreases, and eventually the ions recombine into molecular Hydrogen. During recombination, there is a 50% chance that a H-alpha photon will be released, which can be seen from Earth. Further from the star, the recombination rate matches the ionization rate, marking the edge of the cloud.
Today is also the 25th anniversary of the ‘pale blue dot’ image of Earth, famously snapped by the Voyager 1 spacecraft along with images of the other solar system planets, in what is known as the ‘family portrait.’
Happy love day!