Apollo 16 view of the Earth taken with a hand-held Hasselblad camera about an hour and a half after translunar injection on 16 April, 1972. Most of the United States is visible at right center, including Lake Michigan and Lake Superior and Florida. Mexico and part of Central America are also visible. The slightly different shade of blue below Florida is the Bahama Banks. The Earth is 12,740 km in diameter and north is at roughly 1:00. (Apollo 16, AS16-118-18885)


Location & Time Information
Date/Time (UT): 1972-04-16
Distance/Range (km): N/A
Central Latitude/Longitude (deg): +35.,110.
Orbit(s): N/A

Imaging Information
Area or Feature Type: global view, clouds, water
Instrument: Hasselblad Camera
Instrument Resolution (pixels): Film Type – 70 mm
Instrument Field of View (deg): N/A
Filter: None
Illumination Incidence Angle (deg): N/A
Phase Angle (deg): N/A
Instrument Look Direction: N/A
Surface Emission Angle (deg): N/A

Ordering Information
CD-ROM Volume: N/A
NASA Image ID number: AS16-118-18885
Other Image ID number: N/A
NSSDC Data Set ID (Photo): 72-031A-01F
NSSDC Data Set ID (CD): N/A
Other ID: N/A
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Updated 29 January 2003, DRW.


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Image catalogue Earth

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Apollo 16

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Foucault pendulum

1851 Paris Observatory proof of rotation

The pendulum’s swing rotated clockwise 11° per hour, making a full circle in 32.7 hours.

Amundsen–Scott South Pole Station (click image to Wiki)

South Pole Foucault Pendulum – Winter, 2001

Principal Investigators: Mike Town, Ph.D. candidate, University of Washington; John Bird, Ph.D., FBIS, P.Eng, York University; R. Allan Baker, Sonoma State University

A Foucault Pendulum at the South Pole was determined to have a period of 24 hours, ± 50 minutes.

“Standing on the bottom of the world the Earth spins backward relative to the direction it spins in the Northern Hemisphere. Our first attempt with the pendulum showed the Earth spinning backward from what was expected. We didn’t notice this at first because we’re all from the Northern Hemisphere and are accustomed to the earth spinning in an anticlockwise direction. We then realized that from our frame of reference the earth should be spinning clockwise so we had to modify the pendulum. At an altitude of 11,000+ feet we think a bit more slowly.

The air resistance against this weight caused the pendulum itself to rotate. This gave us spurious results for our first attempt. Later we fashioned the weight so that it was hanging horizontally to the plane of the floor and we got results consistent with what was expected. Our second attempt showed the earth rotating in the proper direction but at an angular velocity twice what is expected (i.e., 12 hour days instead of 24).  Our last attempt showed that the earth spins on its axis once every 24 hours, as expected.

It was difficult to make the pendulum swing in a plane instead of an ellipse. After several attempts with various techniques of holding the bob and dropping it we always got some kind of ellipse instead of a plane. This adds to our error because it is more difficult to locate and mark the pendulum arc’s apex. “



International Earth Rotation and Reference Systems Service established in 1987 by the International Astronomical Union and the International Union of Geodesy and Geophysics.  IERS provides data on Earth orientation, on the International Celestial Reference System/Frame, on the International Terrestrial Reference System/Frame, and on geophysical fluids.

“The variability of the earth-rotation vector relative to the body of the planet is caused by the gravitational torque exerted by the Moon, Sun and planets, displacements of matter in different parts of the planet and other excitation mechanisms. The observed oscillations can be interpreted in terms of mantle elasticity, earth flattening, structure and properties of the core-mantle boundary, rheology of the core, underground water, oceanic variability, and atmospheric variability on time scales of weather or climate.

The International Celestial Reference System

The International Terrestrial Reference System

Observation techniques

Global Positioning System (GPS) – Satellite Laser Ranging (SLR) – Lunar Laser Ranging (LLR) – Very Long Baseline Radio Interferometry (VLBI) – Doppler Orbitography and Radiopositioning – Integrated by Satellite (DORIS)

whatBarycentric Dynamic Time (click image for source)

Sidereal time or star time

A solar day is exactly 24 hours (of solar time). The Earth must rotate an extra 0.986 degrees between solar crossings of the meridian. In 24 hours of solar time, the Earth rotates 360.986 degrees. Sidereal time is based on the Earth’s rate of rotation relative to fixed stars. A mean sidereal day is 23 hours, 56 minutes, 4.0916 seconds (23.9344699 hours or 0.99726958 mean solar days), the time it takes the Earth to make one rotation relative to the vernal equinox. The longer “true” sidereal period is called a stellar day.

US Naval Observatory  “Sidereal time is the hour angle of the vernal equinox, the ascending node of the ecliptic on the celestial equator. The daily motion of this point provides a measure of the rotation of the Earth with respect to the stars, rather than the Sun. Local mean sidereal time is computed from the current Greenwich Mean Sidereal Time plus an input offset in longitude (converted to a sidereal offset by the ratio 1.00273790935 of the mean solar day to the mean sidereal day.) Applying the equation of equinoxes, or nutation of the mean pole of the Earth from mean to true position, yields local apparent sidereal time. Astronomers use local sidereal time because it corresponds to the coordinate right ascension of a celestial body that is presently on the local meridian.”

The moon and sun are moving parallel to the horizon in the video collection of the Amundsen-Scott station provided by the Earth System Research Laboratory Global Monitoring Division (U.S. Department of Commerce | National Oceanic and Atmospheric Administration) link

Latitude: 90.00° South
Longitude: 59° East
Elevation: 2840 masl
Cooperating Agencies: National Science Foundation

The time-lapse video collection has no updates in 2015.  link


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Scott SouthPole



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