1910 – Birth of Indian astronomer Subramanyan Chandrasekhar in Lahore. Chandrasekhar studied at Cambridge University, but spent most of his working life at the University of Chicago. He is mostly remembered by the astronomical community for showing that a white dwarf star cannot support a mass greater than 1.44 times that of the Sun. This is now called the Chandrasekhar limit. If the star has a mass in excess of this limit, it will eventually collapse to form a neutron star or a black hole.
2008 – Launch of the Interstellar Boundary Explorer (IBEX) from Vandenberg Air Force Base, to do exactly what the name suggests: explore the boundary between the Solar System and interstellar space.
It is a common misconception that “outer space” is empty: it isn’t; it’s just that the gas molecules and grains of dust within it are very small, and much further apart than we are used to in this seething mass of atomic activity we call home. These spaced out space particles are known as the interstellar medium (ISM). The mission for IBEX is to measure where the influence of the ISM outweighs that of the Sun’s own stream of particles, the solar wind. This “termination shock” of the solar wind is the place where, as it gets farther from the Sun, and its pressure reduces under the increasing influence of the ISM, it slows to less than the speed of sound.