APOD 4.8

Monday marked a celebratory event: the first sunspots of 2013! Found in the active region AR1748, four sunspots surged within the span of under 48 hours, (going clockwise from the left, the four were documented in extreme ultraviolet, captured at the Solar Dynamics Observatory). Sunspots are ranked by peak brightness in the X-Ray spectrum, with X-class flares typically acting as a prelude to a coronal mass ejection. Three of the four did reach this point, but were not aimed at Earth; the fourth might just braze Earth's magnetic field and disrupt a few radio broadcasts. But this region isn't done yet, likely having a few more flares up its sleeve for later in the year.

Jan H Oort Biography

In the year 1900, on April 28th, Jan H Oort was born in Franker, Friesland, the Dutch province. He later grew up to study in the city of Groningen alongside Jacobus Kapteyn, with a Ph D thesis titles "Stars with High Velocity".

In 1924, Oort discovered the galactic halo, the clusters of stars outside the disk of the Milky Way. By 1927, Oort provided evidence of Bertil Linndblad's theory of the Milk Way's rotation through close observation of the stars; as well as calculating the centre of the Milky Way being at 5 900 parsecs in the direction of Sagittarius.

1932 marked the first proof of dark matter, provided by Oort. He resolved that the mass of the universe cannot be made up of all mass we can see; there must be more than that. The mass of the Milky Way is 100 billion times that of the sun, and not all of that is evidently visible in the disk. His studies of star motion further proved his point.

In the solar system, there is a home to comets that was hypothesised by Oort, and has been dubbed the Oort Cloud following its discovery. The spherical cloud is primarily composed of ices--water, ammonia, and methane. It lies roughly a light-year from the sun.

He discovered polarised light from the Crab Nebula, seen through a synchrotron spectrum.

Among his awards and honours are the Bruce Medal, The Gold Medal of the Royal Astronomical Society, the Karl Schwarzchild Medal, and the Balzan Prize.

When Oort passed on November 5th, 1992, the renowned astrophysist Subrahmanyan Chandreskhar said "The great oak of Astronomy has felled, and we are lost without its shadow."

APOD 4.7

In October of 1604, the famed astronomer Johannes Kepler saw a supernova before his very eyes; this namesake stuck to the remnant. While this explosion of celestial wonder baffled the olden times astronomer and his contemporaries, modern day astronomers are taking advantage of their technological advantage and looking at the nebula in all spectra. This photograph in particular shows the false coloured X-Ray image of it. The cause of this supernova has been deemed a white dwarf in a mass transfer system with a red giant, its binary partner who aided the former star in exceeding Chandrasekhar's limit.

APOD 4.6

From the Stone Tree--known also as Roque Cinchado--situated on the Spanish Canary Island of Tenerife, the central band of the Milky Way can be seen arcing across the sky. With this cooled volcanic formation to the left, the right displays several gems of the summer sky.