Astrometry, definition and study. A-Z index of Cognitio.

Astrometry is the field of astronomy that deals with the measurements, positions, distances and movements of stars and other celestial bodies.

Among the various objectives of astrometry, there is the construction of a scale of cosmic distances.

Besides the fundamental function of providing astronomers with a precise reference system on which to base observations, astrometry is also at the base of celestial mechanics, stellar dynamics and galactic astronomy. Astrometry is essential to keep track of time, since the UTC time zone represents the International Atomic Time synchronized with the rotation of the Earth, obtained thanks to extremely precise astrometric observations.

Earth origins, definition and study. A-Z index of Cognitio.

Earth origins

Thanks to it, over the centuries there have been important steps forward in science and technology. An example of more recent development was the use of Cepheid variables to measure nebulous distances. This led to the discovery of galaxies external to ours by Edwin Hubble who used the parallax method on neighboring Cepheid’s, and was thus able to correlate their period of variation with their absolute luminosity.

Galaxy, definition and study. A-Z index of Cognitio.

Galaxy

Measuring therefore the period and the apparent luminosity of the Cepheid’s present in the nebulae, he managed to determine their distance, coming to formulate what was called the Hubble law, which is still one of the fundamental properties of the Universe. The latest development of astrometry is represented by its application to space technology: from 1989 to 1993 the Hipparcos satellite of the European Space Agency

Hipparcos satellite of the European Space Agency

Hipparcos satellite of the European Space Agency

collected accurate astrometric measurements that led to the compilation of a catalog with more than a million stars, with positions accurate up to 20 or 30 thousandths of a second of arc.

Mu Cephei, also known by the names of star Grenade, in the constellation of Cepheus, is the largest of the stars visible to the naked eye. VY Canis Majoris, in the larger dog, considered to be of greater mass, is instead completely invisible to the naked eye. Moreover, according to some recent measures, the size of the latter would be lower, not higher than the Star Grenade.  No star of comparable size is close enough to the Solar System to allow a precise measurement of its distance.

Solar system, definition and study. A-Z Index of Cognitio.

Solar system

And the dimension that we can deduce for a star varies precisely as a function of its distance from us: an error in the determination of distance has repercussions in a similar uncertainty on its radius. For this reason until the astrometric satellites – in particular the Gaia satellite, ESA launched in December 2013

Gaia satellite, ESA launched in December 2013

Gaia satellite, ESA launched in December 2013

Will not give much better measurements of the space that separates us from distant stars, we will not be able to draw precise conclusions about their size.

Astrometry, definition and study. A-Z index of Cognitio.

© ALL RIGHTS RESERVED

 

To open the video  click on the image, good view from your Alessandro Brizzi.



Astrometry, definition and study. A-Z index of Cognitio.

Astrometry