Here's How Cool a Star Can Be and Still Achieve Success

[Mercury]

by Ken Croswell

The motions of nearby stars reveal the boundary between red dwarfs and brown dwarfs: a surface temperature of 1500 to 1700 Kelvin.

Link: Science News

[neufer]

by Ken Croswell

The motions of nearby stars reveal the boundary
between red dwarfs and brown dwarfs:
a surface temperature of 1500 to 1700 Kelvin.

Link: Science News

The Soldier with the Green Whiskers

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<<Beryllium (melting point: 1560 K) is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. Beryllium is a relatively rare element, usually occurring as a product of the spallation of larger atomic nuclei that have collided with cosmic rays. The world's annual beryllium production of 220 tons is usually manufactured by extraction from the mineral beryl [i.e., beryllium aluminium cyclosilicate:(Be₃Al₂(SiO₃)₆)], a difficult process because beryllium bonds strongly to oxygen.

Notable gemstones high in beryllium include beryl (aquamarine, emerald) and chrysoberyl. In the center of the Emerald City is the Royal Palace of Oz. In the first book, The Wonderful Wizard of Oz (1900), the walls are green, but the city itself is not. However, when they enter, everyone in the Emerald City is made to wear green-tinted spectacles. This is explained as an effort to protect their eyes from the "brightness and glory" of the city, but in effect makes everything appear green when it is, in fact, "no more green than any other city".

The James Webb Space Telescope has an expected mass about half of Hubble Space Telescope's, but its primary mirror, a 6.5 meter diameter gold-coated beryllium reflector will have a collecting area over six times as large. The metal Beryllium was chosen for a number of reasons including weight, but also for its low-temperature coefficient of thermal expansion compared to glass. Other infrared telescopes that have used beryllium mirrors include IRAS, COBE, and Spitzer.

Because of its low atomic number and very low absorption for X-rays, the oldest and still one of the most important applications of beryllium is in radiation windows for X-ray tubes. Extreme demands are placed on purity and cleanliness of beryllium to avoid artifacts in the X-ray images. Thin beryllium foils are used as radiation windows for X-ray detectors, and the extremely low absorption minimizes the heating effects caused by high intensity, low energy X-rays typical of synchrotron radiation. Vacuum-tight windows and beam-tubes for radiation experiments on synchrotrons are manufactured exclusively from beryllium.

Low atomic number also makes beryllium relatively transparent to energetic particles. Therefore, it is used to build the beam pipe around the collision region in particle physics setups, such as all four main detector experiments at the Large Hadron Collider (ALICE, ATLAS, CMS, LHCb), the Tevatron and at SLAC. The low density of beryllium allows collision products to reach the surrounding detectors without significant interaction, its stiffness allows a powerful vacuum to be produced within the pipe to minimize interaction with gases, its thermal stability allows it to function correctly at temperatures of only a few degrees above absolute zero, and its diamagnetic nature keeps it from interfering with the complex multipole magnet systems used to steer and focus the particle beams.>>