The major astronomy news from today has to be the amazing image of the disc surrounding HL Tau taken by the Atacama Large Millimeter/submillimeter Array (ALMA).  This budding solar system lies approximately 450 light-years from Earth in the constellation Taurus.  

Up until today, the best image I have seen of a protoplanetary disc, that wasn't an "artist's rendition", is the image of the nearly face-on disc of TW Hydrae captured by the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer (NICMOS).  The Hubble image, while impressive, lacks the resolution and subtle details apparent in the ALMA image.  Keep in mind, the Hubble image is made from light in the near-infrared wavelength captured with an optical telescope.  ALMA "sees" radiation at wavelengths of a few hundred micrometers to about 1 millimeter, which is near the boundary on the electromagnetic spectrum between infrared and radio waves.  But, instead of using glass and mirrors to capture and focus light, ALMA uses antennas that look like big satellite dishes.  And, here's where ALMA gets really interesting, the antennas are somewhat portable and reconfigurable.  For imaging HL Tau, individual 12-meter antennas were precisely arranged and pointed to create a single dish 15 kilometers across.  Even though Hubble is above the Earth's atmosphere, it's 2.4 meter aperture can't compete with the resolving power of an imaging system that is 15 kilometers across!  

"Aperture fever" is the notion that all amateur astronomers eventually reach a mental state where we are convinced that we must have a bigger piece of glass or a larger mirror.  Why?  Because the larger the aperture, the more light is collected by the instrument leading to better views through an eyepiece or more photons hitting a CCD.  The professionals know this as well.  It is why we see larger and larger optical instruments being proposed and built.  The first of these next generation super Earth-based telescopes to come online will be the Thirty Meter Telescope (TMT) on the summit of Mauna Kea in Hawaii.  It will have a mirror made up of 492 hexagonal segments that spans 30 meters.  This will give it the ability to collect more than 10 times the light of one of the 10 meter Keck telescopes, also on Mauna Kea's summit.  It will have 144 times the light gathering power and 10 times the spatial resolution of the Hubble Space Telescope.  The TMT won't hold the aperture crown for long however, the European Extremely Large Telescope (E-ELT) will be hot on its heels with a 39 meter instrument located at Cerro Armazones in the Atacama Desert of northern Chile.

Seeing this incredible planet-forming disc around HL Tau and comparing it to the earlier attempts made by smaller aperture instruments truly does highlight the value of larger apertures.  It's clear to me that the big boys all have aperture fever and someday you may too...don't say I didn't warn you!

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