THE SOUTHWORTH PLANETARIUM
70 Falmouth Street      Portland, Maine 04103
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43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded
January 1970
2021-2022: CXXXVIII
"What's wrong with being the true you? Simple. Authenticity is among the
most frightening of all human experiences. To be wholly and
unapologetically yourself is to invite scorn and accept exclusion. Hence,
hardly anyone truly attempts it. Lamentably so, for though humans may be
tribal at heart, they are unique at soul. To find the courage to exhibit
one's true self and as a consequence embrace rejection should be the
principal aim of the individual. For, the only prospect more terrifying
than ostracization is that of being on your deathbed while knowing that the
inner you never lived at all."



THE DAILY ASTRONOMER
Thursday, June 16, 2022
The Other Redshift

Today, we return to Pandora's Jar for a question about another type of
red-shifting: one that is unrelated to the motion of galaxies.


*"I know that galaxies have redshifts when they move away from us. But, why
is light from the Sun and other stars and even planets 'red-shifted?'" *
* -Malcolm. B, Saco*


Yes,  galaxies exhibit a redshift because the light they emit is "stretched
out" due to their recessional motion.     This elongation causes the
light's wavelength to increase.     Because red waves are longer than blue
waves,  light emitting objects whose waves experience a motion-induced
elongation are said to be "red-shifted."

However, scientists recognize another type of red-shift known as
"gravitational red-shifting."  This red-shifting effect occurs when light
moves away from a massive body.  That body's gravitational pull diminishes
the light's energy.   Because light speed remains constant, that energy
reduction increases the light's wavelength.     A photon's energy is
proportional to its frequency and inversely proportional to its
wavelength.     The longer the wavelength, the lower the energy.

[image: Sun-Earth-Moon.jpg]
The gravitational red-shifting caused by the Sun's gravity is so slight
(two millionths of a wavelength) that it was only measured in 2020.


In theory, every star's light experiences some gravitational red-shifting
because every star is massive.  However, that effect is slight.  For the
Sun, that effect accounts for two-millionths of a wavelength.   This
red-shift is so small it was only finally measured in 2020 by a research
team with the  Instiuto de Astrofisica de Canarias (The Astrophysics
Institute of the Canary Islands).

Red-shifts around more massive stars and other bodies are more substantial
by virtue of their greater mass.      This effect was discovered with the
development of General Relativity, the theory which posits that matter
distorts its local space-time geometry and so can affect the pathways of
light.


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