USNO Leads the Way in Aligning the Sky

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USNO Leads the Way in Aligning the Sky

Post by bystander » Sat Sep 08, 2018 12:43 am

USNO Leads the Way in Aligning the Sky
U.S. Naval Observatory | 2018 Sep 07

On August 30th, the International Astronomical Union (IAU) adopted the International Celestial Reference Frame -- 3 (ICRF3) as the standard reference frame for the celestial background. The IAU voted to adopt ICRF3 effective January 1, 2019, replacing the current reference frame, ICRF2, which had been adopted in 2009 by the IAU. ICRF3 is a “realization” of an idealized reference frame, tied to the center of mass of our solar system. It is analogous to lines of latitude and longitude on the Earth extended into the sky -- along with actual markers on the surface of the Earth to set those lines. These celestial reference points are used by all astronomers to determine positions and motions of celestial objects. The ICRF is used by Earth-orbiting spacecraft to determine their orientation (or direction of pointing), and by ground stations tracking space probes as they travel through the solar system. The ICRF is also used to measure the motions of the Earth in 3-dimensional inertial space with very high precision, making capabilities such as the Global Positioning System (GPS) possible.

The ICRF3 consists of 4536 extra-galactic “active galactic nuclei” (AGN), which are the supermassive black holes in the center of distant galaxies. They are chosen because they are very bright in radio frequencies, and because they do not appear to wobble or move over time--that is, they are extremely distant and stable reference points. The ICRF3 includes, for the first time, observations in three different radio frequencies: S/X, K and X/Ka, making it the first multi-wavelength reference frame. This is important, as different frequencies support different types of users: the S/X band is used to determine the Earth’s orientation, K is used primarily radio astronomers for astronomical measurements, and X/Ka is used by NASA, ESA, and other space agencies for solar system navigation. ...
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

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GFZ: A New Reference Frame for the Sky

Post by bystander » Thu Sep 13, 2018 4:29 pm

A New Reference Frame for the Sky
GFZ German Research Centre for Geosciences | Helholtz Centre, Potsdam | 2018 Sep 13
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor