This Month in the History of Astronomy - January
- Jan 8, 1942 - Stephen Hawking, British theoretical
astrophysicist who specialized in black holes. Exactly the
opposite of his predecessor in "Newton's chair" at Cambridge,
Fred Hoyle (see June 24th),
Hawking was thoroughly orthodox in his cosmology.
- Jan 10, 1936 - Robert W. Wilson, co-discoverer with
Arno Penzias of the cosmic microwave (3 degree) background;
1978 Physics Nobel Laureate.
- Jan 12, 1830 - The founding of what in 1831 would become
the Royal Astronomical Society, by John Herschel, Charles Babbage,
James South, and several others. The first "AS", the RAS has
published it's Monthly Notices continuously since 1831.
- Jan 19, 1747 - Johann Bode, publicizer of the Titus-Bode
law, a nearly geometric progression of the distances of the planets
from the Sun.
- Jan 19, 1851 - Jacobus Kapteyn, Dutch astronomer who
compiled data on the positions and brightnesses of 455,000 stars,
primarily in the Southern hemisphere, and transformed them into
distributions and motions to create the first modern model
of the size, structure, and dynamics of the Milky Way Galaxy.
- Jan 20, 1573 - Simon Mayr, who observed the moons
of Jupiter at nearly the same time as Galileo and gave them
the Greek names in use today (see below).
- Jan 21, 1792 - John Couch Adams, who predicted the
existence of Neptune.
- Jan 21, 1908 - Bengt Strömgren, developer of the
theory of ionization nebulae (H II regions) such as the Orion and
Trifid (M20) nebulas, in which hard ultraviolet radiation from very
hot, O-type stars, photons with ≥13.6 eV energy, ionizes the
surrounding hydrogen gas, heating it up to temperatures of several
thousand degrees Kelvin (up to ~10,000°K).
When the free electrons recombine with the hydrogen ions (bare
protons), they emit light of specific energies (wavelengths) as
they cascade down through the hydrogen atom's energy levels to the
ground state in a number of different ways, yielding the observed
spectrum rich in hydrogen emission lines. [See energy level diagram
at right.] The gas essentially fluoresces by absorbing light of one
wavelength and converting it to light of other, visible wavelengths.
The finite number of UV photons emitted by the stars means the
"Strömgren sphere" will be of finite radius, so if the gas
cloud in which it occurs is of fairly uniform density, the H II
region will look approximately spherical and Strömgren's
equations give its diameter -- or the gas density if the size
can be determined some other way. This is one of the few ways
to get gas densities in star forming regions, since O stars have
such short lifetimes that they're always found where this is an
Strömgren also developed a system of medium bandwidth
photoelectric photometry which allowed stellar spectral
classification without requiring an actual spectrum.
- Jan 24, 1882 - American solar astronomer Harold Babcock,
who proposed that the sunspot cycle was a result of the Sun's
differential rotation and magnetic field (1961).
- Jan 25, 1736 - Joseph Louis Lagrange, famed French
mathematician who made important contributions to the field
of celestial mechanics.
- Jan 28, 1611 - Johannes Hevelius, who published the
Selenographia, the first detailed maps of the Moon (1647).
Discoveries and other firsts
©2002-2017, Chris Wetherill. All rights reserved. Display here does
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