Post on 09-Apr-2018
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Bulk parameters
Mass (1024 kg) 5.9736
Volume (1010 km3) 108.321
Equatorial radius (km) 6378.1
Polar radius (km) 6356.8
Volumetric mean radius (km) 6371.0Core radius (km) 3485
Ellipticity (Flattening) 0.00335
Mean density (kg/m3) 5515
Surface gravity (m/s2) 9.798
Surface acceleration (m/s2) 9.780
Escape velocity (km/s) 11.186
GM (x 106 km3/s2) 0.3986
Bond albedo 0.306
Visual geometric albedo 0.367
Visual magnitude V(1,0) -3.86
Solar irradiance (W/m2) 1367.6
Black-body temperature (K) 254.3
Topographic range (km) 20
Moment of inertia (I/MR2) 0.3308
J2 (x 10-6) 1082.63
Number of natural satellites 1
Planetary ring system No
Orbital parameters
Semimajor axis (106 km) 149.60
Sidereal orbit period (days) 365.256
Tropical orbit period (days) 365.242
Perihelion (106 km) 147.09
Aphelion (106 km) 152.10Mean orbital velocity (km/s) 29.78
Max. orbital velocity (km/s) 30.29
Min. orbital velocity (km/s) 29.29
Orbit inclination (deg) 0.000
Orbit eccentricity 0.0167
Sidereal rotation period (hrs) 23.9345
Length of day (hrs) 24.0000
Obliquity to orbit (deg) 23.44
Earth Mean Orbital Elements (J2000)
Semimajor axis (AU) 1.00000011
Orbital eccentricity 0.01671022
Orbital inclination (deg) 0.00005
Longitude of ascending node (deg) -11.26064
Longitude of perihelion (deg) 102.94719
Mean Longitude (deg) 100.46435
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North Pole ofRotation
Right Ascension: 0.00 - 0.641T
Declination : 90.00 - 0.557T
Reference Date : 12:00 UT 1 Jan 2000 (JD 2451545.0)
T = Julian centuries from reference date
Terrestrial Magnetosphere
Dipole field strength: 0.3076 gauss-Re3
Latitude/Longitude of dipole N: 78.6 degrees N/70.1 degrees W
Dipole offset (planet center to dipole center) distance: 0.0725 Re
Latitude/Longitude of offset vector: 18.3 degrees N/147.8 degrees E
Note: Re denotes Earth radii, 6,378 km
Terrestrial Atmosphere
Surface pressure: 1014 mb
Surface density: 1.217 kg/m3
Scale height: 8.5 km
Total mass of atmosphere: 5.1 x 1018 kg
Total mass of hydrosphere: 1.4 x 1021 kg
Average temperature: 288 K (15 C)
Diurnal temperature range: 283 K to 293 K (10 to 20 C)
Wind speeds: 0 to 100 m/s
Mean molecular weight: 28.97 g/mole
Atmospheric composition (by volume, dry air):Major : 78.08% Nitrogen (N2), 20.95% Oxygen (O2),
Minor (ppm): Argon (Ar) - 9340; Carbon Dioxide (CO2) - 380
Neon (Ne) - 18.18; Helium (He) - 5.24; CH4 - 1.7
Krypton (Kr) - 1.14; Hydrogen (H2) - 0.55
Numbers do not add up to exactly 100% due to roundoff and uncertainty
Water is highly variable, typically makes up about 1%
The Moon
For information on the Moon, see the Moon
Fact Sheet
Notes on the factsheets - definitions of parameters, units, notes on sub- and
superscripts, etc.
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Planetary Fact Table - metric unitsPlanetary Fact Table - U.S. units
Planetary Fact Table - Earth ratio
Earth PageDirectory to o
Discovered By Known by the Ancients
Date of Discovery Unknown
Average Distance from the Sun Metric: 149,597,890 km
English: 92,955,820 miles
Scientific Notation: 1.4959789 x 108km (1.000 A.U.)
Perihelion (closest) Metric: 147,100,000 km
English: 91,400,000 miles
Scientific Notation: 1.471 x 108km (0.983 A.U.)
Aphelion (farthest) Metric: 152,100,000 km
English: 94,500,000 miles
Scientific Notation: 1.521 x 108km (1.017 A.U.)
Equatorial Radius Metric: 6,378.14 km
English: 3,963.19 miles
Scientific Notation: 6.37814 x 103 km
By Comparison: 1 x Earth's
Equatorial Circumference Metric: 40,075 km
English: 24,901 miles
Scientific Notation: 4.0075 x 104 km
Volume Metric: 1,083,200,000,000 km3
English: 259,900,000,000 mi3
Scientific Notation: 1.0832 x 1012km3
By Comparison: 1 x Earth's
Mass Metric: 5,973,700,000,000,000,000,000,000 kg
Scientific Notation: 5.9737 x 1024 kg
Density Metric: 5.515 g/cm3
Surface Area Metric: 510,065,700 km2
English: 196,937,500 square miles
Scientific Notation: 5.100657 x 108km2
Equatorial Surface Gravity Metric: 9.766 m/s2
English: 32.041 ft/s2
Escape Velocity Metric: 40,248 km/h
English: 25,009 mph
Scientific Notation: 11,180 m/s
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Sidereal Rotation Period (Length of Day) 0.99726968 Earth days
23.934 hours
Sidereal Orbit Period (Length of Year) 1.0000174 Earth years
365.24 Earth days
Mean Orbit Velocity Metric: 107,229 km/h
English: 66,629 mph
Scientific Notation: 29,785.9 m/s
Orbital Eccentricity 0.01671022
Orbital Inclination to Ecliptic 0.00005 degrees
Equatorial Inclination to Orbit 23.45 degrees
Orbital Circumference Metric: 924,375,700 km
English: 574,380,400 miles
Scientific Notation: 9.243757 x 108km
Minimum/Maximum Surface Temperature Metric: -88/58 (min/max) C
English: -126/136 (min/max) FScientific Notation: 185/331 (min/max) K
Atmospheric Constituents Nitrogen, Oxygen
Scientific Notation: N2, O2
By Comparison: N2is 80% of Earth's air and is a crucial element in DNA
ther Planetary Fact Sheets
Planetary Symbol: Surface Gravity: 9.78 m/s^2
Diameter:12,753 km (7,926miles)
Rotation Period with respect to
Sun (Length ofDay):24 hrs
Mass:
5.98x10^24
kilograms(6.5e21 tons)
Rotation Period with respect to
stars (Sidereal Day):
23 hrs 56
min
Density: 5,515 kg/m^3Revolution Period about the Sun
(Length ofa Year):
365 days 5
hrs
Minimum Distance
from Sun:
146 million km(91 million miles)
Tilt ofAxis: 23o 27"
Maximum Distance
from Sun:
152 million km(94.5 million miles)
Temperature:
-89o
C to57.7oC(-128
oF to
136oF)
Orbital Semimajor
Axis:1.0 AU Average Surface Temperature (K): 287K
Satellites: 1 (the Moon)
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Sun Reference Data
Diameter:1.4 million km
(870,000 miles)Age: 4.5 billion years
Mass: 330,000 x Earth Distance from Earth:149.6 million km (93
million miles)
Density: 1.41 (water=1)Distance to Nearest
Star:4.3 light years
Solar Wind Speed: 3 million km/hr. Luminosity:390 billion billion
megawatts
Solar Cycle: 8 - 11 yearsTemperature at
surface:5,500
oC (9,932
oF)
Temperature at
Core:
14 milliono
C (22.5
milliono
F)
Temperature of
Sunspots:4,000
oC (7,232
oF)
Rotation Period at
Equator:25 Earth days
Rotation Period at
Poles:35 Earth days
The North Star, also called the Pole Star or Polaris, is the star that theearth's axis points toward in the Northern sky. For many years, people have
been fascinated with this star and the fact that it doesn't seem to move inthe sky. Some have created legends explaining why the star stands still. As
more detailed scientific instrumentation has become available, scientistshave begun to study more about Polaris. Surprisingly, it is a rich subject
consisting of a binary star system.
Why Do We Care about the North Star?
For many years, the North Star has been used as a navigation aid and to
chart navigational maps. It has also been used to measure astronomicallatitude since we map latitudes to the equivalent sky positions: the North
Pole equates to +90 degrees latitude on Earth as does its projection into thesky. In addition to these functional uses, over time many cultures have built
folklore around the North Star. Even people with little interest in astronomyor mapmaking know about the North Star, and some have created stories
explaining why it seemingly never moves.
The most famous story about the North Star is the Native American mythexplaining why the North Star stands still. In this story, a brave son Na-Gah
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tried to impress his father by climbing the tallest cliff he could find. Through
difficult conditions he persisted until he found himself at the top of a very
high mountain. The mountain was so tall that Na-Gah looked down on all theother mountains. Unfortunately, there was no way down. When his father
came looking for him, he found Na-Gah stuck high above. Not wanting his
son to suffer for his bravery, he turned Na-Gah into a star that can be seenand honored by all living things.
Polaris: The Current North Star
Today the Earth's axis points within one degree of Polaris, the brightest star
in the constellation Ursa Minor (also called the Little Bear or the LittleDipper). Polaris appears to be in a fixed position in the sky throughout the
year. All other stars and constellations seem to revolve around the North
Star.
To find Polaris in the sky, locate the Big Dipper and follow the two stars atthe end of the basin upward. This should lead you directly to Polaris. It is the
last star in the tail of the Little Dipper.
Why isn't the North Star Fixed?
Over the course of time, the North Star changes. Right now Polaris is withinone degree of true north, but at other times the North Star has been and will
again be Thuban (the brightest star in the constellation Draco), Vega (the
brightest star in the constellation Lyra), and Alpha Cephei (the brightest star
in the constellation Cepheus).
The North Star changes over time because the direction of the earth's axischanges slowly over time. Since by definition the North Star is the star mostclosely aligned with the earth's axis, as the axis moves the nearest star
changes too.
This type of axis movement is similar to that of a spinning top. As the top
slows, the axis of rotation changes as the top draws out each rotation; that
is to say that the stem of the top itself traces out a circular pattern rather
than pointing at a single spot or staying mostly still. If you draw an
imaginary line of the earth's axis and continue it up to the sky, it will make asimilar path. This type of axis rotation is called precession.
In the case of the earth, precession is caused by the gravitational pull of the
sun and the moon. The earth's axis makes one complete rotation over the
course of approximately 26,000 years. If you trace the path of the axis inthe sky, you will find that Polaris, Vega, Thuban, and Alpha Cephei all fall on
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or very close to it. So when the earth's axis is at a point on the path near
Vega, Vega becomes the North Star while Thuban is the North Star when the
axis is near it on the path.
Five thousand years ago, Thuban was the North Star. Five thousand years
from now, the North Star will be Alpha Cephei. Seven thousand years afterthat, it will be Vega. Nine thousand years after that, Thuban will be the
North Star again. At these dates, the various stars will be at the closest to
absolute north. For some time before, the relevant star will be approachingdue north and it will be receding for some time after the time listed. In these
interim times, the North Star is whichever star is closest to north.
A pole staris a visible star, especially a prominent one, that is approximately aligned with theEarth'saxis
of rotation; that is, a star whose apparent position is close to one of thecelestial poles, and which lies
approximately directly overhead when viewed from the Earth'sNorth Pole orSouth Pole. (A similar
concept also applies to other planets.)