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5+ < title > Planetary Fact Sheet Notes</ title >
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10+ < p > <!-- text and html formatting by drw at n.s.s.d c -->
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12+ < h1 > Planetary Fact Sheet Notes</ h1 >
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14+
15+ < p > < a name ="mass "> </ a >
16+ < p >
17+ < b > Mass</ b > (10< sup > 24</ sup > kg or 10< sup > 21</ sup > tons) - This is the mass of the planet in septillion
18+ (1 followed by 24 zeros) kilograms or sextillion (1 followed by 21 zeros) tons. Strictly speaking tons
19+ are measures of weight, not mass, but are used here to represent the mass of one ton of material under
20+ Earth gravity.
21+ </ p > < a name ="diam "> </ a >
22+ < p >
23+ < b > Diameter</ b > (km or miles) - The diameter of the planet at the equator, the distance through
24+ the center of the planet from one point on the equator to the opposite side, in kilometers or miles.
25+ </ p > < a name ="dens "> </ a >
26+ < p >
27+ < b > Density</ b > (kg/m< sup > 3</ sup > or lbs/ft< sup > 3</ sup > ) - The average density (mass divided by volume) of
28+ the whole planet (not including the atmosphere for the terrestrial planets) in kilograms per cubic meter
29+ or pounds per cubic foot. Strictly speaking pounds are measures of weight, not mass, but are used here to
30+ represent the mass of one pound of material under Earth gravity.
31+ </ p > < a name ="grav "> </ a >
32+ < p >
33+ < b > Gravity</ b > (m/s< sup > 2</ sup > or ft/s< sup > 2</ sup > ) - The gravitational acceleration on the surface at
34+ the equator in meters per second squared or feet per second squared, including the effects of rotation.
35+ For the gas giant planets the gravity is given at the 1 bar pressure level in the atmosphere. The gravity
36+ on Earth is designated as 1 "G", so the Earth ratio fact sheets gives the gravity of the other planets in G's.
37+ </ p > < a name ="escv "> </ a >
38+ < p >
39+ < b > Escape Velocity</ b > (km/s) - Initial velocity, in kilometers per second or miles per second, needed
40+ at the surface (at the 1 bar pressure level for the gas giants) to escape the body's gravitational pull,
41+ ignoring atmospheric drag.
42+ </ p > < a name ="rotp "> </ a >
43+ < p >
44+ < b > Rotation Period</ b > (hours) - This is the time it takes for the planet to complete one rotation
45+ relative to the fixed background stars (not relative to the Sun) in hours. Negative numbers indicate
46+ retrograde (backwards relative to the Earth) rotation.
47+ </ p > < a name ="leng "> </ a >
48+ < p >
49+ < b > Length of Day</ b > (hours) - The average time in hours for the Sun to move from the noon position in the
50+ sky at a point on the equator back to the same position.
51+ </ p > < a name ="dist "> </ a >
52+ < p >
53+ < b > Distance from Sun</ b > (10< sup > 6</ sup > km or 10< sup > 6</ sup > miles) - This is the average distance from
54+ the planet to the Sun in millions of kilometers or millions of miles, also known as the semi-major axis.
55+ All planets have orbits which are elliptical, not perfectly circular, so there is a point in the orbit at
56+ which the planet is closest to the Sun, the perihelion, and a point furthest from the Sun, the aphelion.
57+ The average distance from the Sun is midway between these two values. The average distance from the Earth
58+ to the Sun is defined as 1 Astronomical Unit (AU), so the ratio table gives this distance in AU.< br >
59+ * For the Moon, the average distance from the Earth is given.
60+ </ p > < a name ="peri "> </ a >
61+ < p >
62+ < b > Perihelion, Aphelion</ b > (10< sup > 6</ sup > km or 10< sup > 6</ sup > miles) - The closest and furthest points
63+ in a planet's orbit about the Sun, see "Distance from Sun" above.< br >
64+ * For the Moon, the closest and furthest points to Earth are given, known as the "Perigee" and "Apogee"
65+ respectively.
66+ </ p > < a name ="orbp "> </ a >
67+ < p >
68+ < b > Orbital Period</ b > (days) - This is the time in Earth days for a planet to orbit the Sun from one
69+ vernal equinox to the next. Also known as the tropical orbit period, this is equal to a year on Earth.< br >
70+ * For the Moon, the sidereal orbit period, the time to orbit once relative to the fixed background
71+ stars, is given. The time from full Moon to full Moon, or synodic period, is 29.53 days.
72+ For Pluto, the tropical orbit period is not well known, the sidereal orbit period is used.
73+ </ p > < a name ="orbv "> </ a >
74+ < p >
75+ < b > Orbital Velocity</ b > (km/s or miles/s) - The average velocity or speed of the planet as it orbits the
76+ Sun, in kilometers per second or miles per second.< br >
77+ * For the Moon, the average velocity around the Earth is given.
78+ </ p > < a name ="orbi "> </ a >
79+ < p >
80+ < b > Orbital Inclination</ b > (degrees) - The angle in degrees at which a planets orbit around the Sun is
81+ tilted relative to the ecliptic plane. The ecliptic plane is defined as the plane containing the Earth's
82+ orbit, so the Earth's inclination is 0.
83+ </ p > < a name ="orbe "> </ a >
84+ < p >
85+ < b > Orbital Eccentricity</ b > - This is a measure of how far a planet's orbit about the Sun (or the Moon's
86+ orbit about the Earth) is from being circular. The larger the eccentricity, the more elongated is the
87+ orbit, an eccentricity of 0 means the orbit is a perfect circle. There are no units for eccentricity.
88+ </ p > < a name ="orbo "> </ a >
89+ < p >
90+ < b > Obliquity to Orbit</ b > (degrees) - The angle in degrees the axis of a planet (the imaginary line running
91+ through the center of the planet from the north to south poles) is tilted relative to a line
92+ perpendicular to the planet's orbit around the Sun, north pole defined by right hand rule.< br >
93+ *Venus rotates in a retrograde direction, opposite the other planets, so the tilt is almost 180
94+ degrees, it is considered to be spinning with its "top", or north pole pointing "downward" (southward).
95+ Uranus rotates almost on its side relative to the orbit, Pluto is pointing slightly "down". The ratios
96+ with Earth refer to the axis without reference to north or south.
97+ </ p > < a name ="temp "> </ a >
98+ < p >
99+ < b > Mean Temperature</ b > (C or F) - This is the average temperature over the whole planet's surface
100+ (or for the gas giants at the one bar level) in degrees C (Celsius or Centigrade) or degrees F
101+ (Fahrenheit). For Mercury and the Moon, for example, this is an average over the sunlit (very
102+ hot) and dark (very cold) hemispheres and so is not representative of any given region on the planet,
103+ and most of the surface is quite different from this average value. As with the Earth, there will tend
104+ to be variations in temperature from the equator to the poles, from the day to night sides, and seasonal
105+ changes on most of the planets.
106+ </ p > < a name ="surp "> </ a >
107+ < p >
108+ < b > Surface Pressure</ b > (bars or atmospheres) - This is the atmospheric pressure (the weight of the
109+ atmosphere per unit area) at the surface of the planet in bars or atmospheres.< br >
110+ *The surfaces of Jupiter, Saturn, Uranus, and Neptune are deep in the atmosphere and the location and
111+ pressures are not known.
112+ </ p > < a name ="sats "> </ a >
113+ < p >
114+ < b > Number of Moons</ b > - This gives the number of IAU officially confirmed moons orbiting the planet. New
115+ moons are still being discovered.
116+ </ p > < a name ="ring "> </ a >
117+ < p >
118+ < b > Ring System?</ b > - This tells whether a planet has a set of rings around it, Saturn being the most
119+ obvious example.
120+ </ p > < a name ="magf "> </ a >
121+ < p >
122+ < b > Global Magnetic Field?</ b > - This tells whether the planet has a measurable large-scale magnetic
123+ field. Mars and the Moon have localized regional magnetic fields but no global field.
124+ </ p >
125+ < p >
126+ The term "terrestrial planets" refers to Mercury, Venus, Earth, Moon, Mars, and Pluto.< br >
127+ The term "gas giants" refers to Jupiter, Saturn, Uranus, and Neptune.
128+ </ p >
129+ < p >
130+ < hr >
131+
132+
133+ < a href ="index.html ">
134+ < img alt =" " src ="https://nssdc.gsfc.nasa.gov/bullet/red_bullet_half.gif "> Planetary Fact Sheet - Metric
135+ Units</ a > < br >
136+
137+ < a href ="planet_table_british.html ">
138+ < img alt =" " src ="https://nssdc.gsfc.nasa.gov/bullet/red_bullet_half.gif "> Planetary Fact Sheet - U.S.
139+ Units</ a > < br >
140+
141+ < a href ="planet_table_ratio.html ">
142+ < img alt =" " src ="https://nssdc.gsfc.nasa.gov/bullet/red_bullet_half.gif "> Planetary Fact Sheet - Values compared
143+ to Earth</ a > < br >
144+
145+
146+ < a href ="https://nssdc.gsfc.nasa.gov/planetary/planetfact.html ">
147+ < img alt =" " src ="https://nssdc.gsfc.nasa.gov/bullet/red_bullet_half.gif "> Index of Planetary Fact Sheets</ a >
148+ - More detailed fact sheets for each planet< br >
149+
150+
151+ < hr >
152+
153+ < address >
154+ Author/Curator:< br >
155+ Dr. David R. Williams, < a href ="mailto:dave.williams@nasa.gov "> dave.williams@nasa.gov</ a > < br >
156+ NSSDCA, Mail Code 690.1< br >
157+ NASA Goddard Space Flight Center< br >
158+ Greenbelt, MD 20771< br >
159+ +1-301-286-1258< br >
160+ </ address >
161+ < br clear ="left ">
162+ < hr >
163+ < h6 > NASA Official: Dave Williams, david.r.williams@nasa.gov< br >
164+
165+
166+ Last Updated: 20 December 2021, DRW</ h6 >
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