International Celestial Reference Frame in the context of "Universal Time"

Play Trivia Questions online!

 or

Skip to study material about International Celestial Reference Frame in the context of "Universal Time"
Ad spacer

⭐ Core Definition: International Celestial Reference Frame

The International Celestial Reference System (ICRS) is the current standard celestial reference system adopted by the International Astronomical Union (IAU). Its origin is at the barycenter of the Solar System, with axes that are intended to "show no global rotation with respect to a set of distant extragalactic objects". The coordinates are basically the declination and right ascension based on the mean celestial equator and mean celestial equinox at the J2000 epoch.

The International Celestial Reference Frame (ICRF) is a realization of the International Celestial Reference System using reference celestial sources observed at radio wavelengths. In the context of the ICRS, a reference frame (RF) is the physical realization of a reference system, i.e., the reference frame is the set of numerical coordinates of the reference sources, derived using the procedures spelled out by the ICRS.

↓ Menu

>>>PUT SHARE BUTTONS HERE<<<

👉 International Celestial Reference Frame in the context of Universal Time

Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle (ERA, which serves as the replacement for Greenwich Mean Sidereal Time). UT1 is the same everywhere on Earth. UT1 is required to follow the relationship

where Tu = (Julian UT1 date − 2451545.0).

↓ Explore More Topics
In this Dossier

International Celestial Reference Frame in the context of Proper motion

Proper motion is the angular speed of a celestial object, such as a star, as it moves across the sky. It is an astrometric measure, giving an object's change in angular position over time relative to the center of mass of the Solar System. This parameter is measured relative to the distant stars or a stable reference such as the International Celestial Reference Frame (ICRF). Patterns in proper motion reveal larger structures like stellar streams, the general rotation of the Milky Way disk, and the random motions of stars in the Galactic halo.

The components for proper motion in the equatorial coordinate system (of a given epoch, often J2000.0) are given in the direction of right ascension (μα) and of declination (μδ). Their combined value is computed as the total proper motion (μ). It has dimensions of angle per time, typically arcseconds per year or milliarcseconds per year.

↑ Return to Menu
LINKED FROM (PARENTS)
← Proper motion ← Universal Time
LINKS TO (CHILDREN)
Celestial reference system → International Astronomical Union → Barycenter → Solar System → Declination → Right ascension → Celestial equator → Celestial equinox → J2000 → Frame of reference →