The parsec is defined to be the distance at which one Astronomical Unit (q.v.)
subtends an angle of one second of arc (of which 3600 make one degree); this
makes it about a fifth of a million AU, which is about 3.26 light years.
This choice of unit arises naturally from determining the distance from Earth to
a star by measuring parallax - the direction to the star, as the Earth goes
around its orbit, will vary by the angle subtended by two AU (the diameter of
Earth's orbit) at the distance between Earth and the star; and actual stars vary
in direction by up to of order one arc second. Dividing two arc seconds by a
star's observed angle of variation yields the number of parsecs to the star; the
nearest stars are modest multiples of a parsec away.
See the doc string of AU for further details.
""")
parsec.observe(30.857 * peta * metre) # Kaye & Laby
# some other source alleged 3.26 * year.light, which is about the same.
Sun.luminosity = Sun.bright * 4 * pi * AU**2
Sun.bright.also(pressure = Quantity(2 * second / second.light, Sun.bright,
"""Photon pressure from the Sun at Earth.
The light from the sun carries momentum as well as energy. If we put a mirror
in the path of the sun-light to reflect all of the light back to the sun, all
of that momentum gets reversed, so the mirror receives twice the momentum of
the light, thereby exerting a pressure equal to 2/c times the incident power,
Sun.bright. This works out at about five micro-Pascal at Earth's orbit.
"""))
# surface part data taken from Asimov:
_square_kilo_mile = (kilo * mile)**2
# I haven't yet found radius ... but its eccentricity is low
orbit=Orbit(Sun, Float(4, 0, 9, mile), None, 0),
magnitude=18.5,
discovery=Discovery("Chadwick Trujillo and Michael Brown, of Caltech",
2002,
telescope = "Palomar Oschin Schmidt",
note = """2002 LM60, a.k.a. Quaoar
Drs. Trujillo and Brown first observed this Kuiper Belt object, then (July 5,
August 1) had the Hubble Space Telescope take a closer look, to determine true
angular size, 40 * milli * arc.second. They named it after the creator-god of
the Tongva, the original inhabitants of the Los Angeles basin.\n"""))
# Even further out: beyond Kuiper, in the "inner Oort Cloud"
ape = Quantity(900, AU)
ape.observe(130 * tera * metre)
ape.observe(84 * giga * mile)
peri = About(76, 7, AU)
Sedna = MinorPlanet('Sedna',
surface=Spheroid(About(950, 150, mile),
# surface temperature is "about" -400 F.
temperature=Fahrenheit(About(-400, 10)),
# it "likely rotates once every approximately 40 days"
#' suggesting that it's tidally locked to a moon
spin=Spin(About(40, 5, day))),
orbit=Orbit(Sun,
Quantity.flat(peri.low, ape.high,
.5 * (ape.best + peri.best)),
Spin(10.5 * kilo * year),
perihelion=peri, apehelion=ape),
discovery=Discovery(
The parsec is defined to be the distance at which one Astronomical Unit (q.v.)
subtends an angle of one second of arc (of which 3600 make one degree); this
makes it about a fifth of a million AU, which is about 3.26 light years.
This choice of unit arises naturally from determining the distance from Earth to
a star by measuring parallax - the direction to the star, as the Earth goes
around its orbit, will vary by the angle subtended by two AU (the diameter of
Earth's orbit) at the distance between Earth and the star; and actual stars vary
in direction by up to of order one arc second. Dividing two arc seconds by a
star's observed angle of variation yields the number of parsecs to the star; the
nearest stars are modest multiples of a parsec away.
See the doc string of AU for further details.
""")
parsec.observe(30.857 * peta * metre) # Kaye & Laby
# some other source alleged 3.26 * year.light, which is about the same.
Sun.luminosity = Sun.bright * 4 * pi * AU**2
Sun.bright.also(pressure = Quantity(2 * second / second.light, Sun.bright,
"""Photon pressure from the Sun at Earth.
The light from the sun carries momentum as well as energy. If we put a mirror
in the path of the sun-light to reflect all of the light back to the sun, all
of that momentum gets reversed, so the mirror receives twice the momentum of
the light, thereby exerting a pressure equal to 2/c times the incident power,
Sun.bright. This works out at about five micro-Pascal at Earth's orbit.
"""))
# surface part data taken from Asimov:
_square_kilo_mile = (kilo * mile)**2
# I haven't yet found radius ... but its eccentricity is low
orbit=Orbit(Sun, Float(4, 0, 9, mile), None, 0),
magnitude=18.5,
discovery=Discovery("Chadwick Trujillo and Michael Brown, of Caltech",
2002,
telescope="Palomar Oschin Schmidt",
note="""2002 LM60, a.k.a. Quaoar
Drs. Trujillo and Brown first observed this Kuiper Belt object, then (July 5,
August 1) had the Hubble Space Telescope take a closer look, to determine true
angular size, 40 * milli * arc.second. They named it after the creator-god of
the Tongva, the original inhabitants of the Los Angeles basin.\n"""))
# Even further out: beyond Kuiper, in the "inner Oort Cloud"
ape = Quantity(900, AU)
ape.observe(130 * tera * metre)
ape.observe(84 * giga * mile)
peri = About(76, 7, AU)
Sedna = MinorPlanet(
'Sedna',
surface=Spheroid(
About(950, 150, mile),
# surface temperature is "about" -400 F.
temperature=Fahrenheit(About(-400, 10)),
# it "likely rotates once every approximately 40 days"
#' suggesting that it's tidally locked to a moon
spin=Spin(About(40, 5, day))),
orbit=Orbit(Sun,
Quantity.flat(peri.low, ape.high, .5 * (ape.best + peri.best)),
Spin(10.5 * kilo * year),
perihelion=peri,
