lpetrich
Contributor
Nearly a year ago, the Gaia spacecraft mission was ended. This spacecraft found the positions of a billion stars with great precision, observing them for 11 years. But the spacecraft was running low on reaction gas, and it would run out by the middle of that year. So it was sent out into a heliocentric orbit, all its data was downloaded, and it was decommissioned.
The spacecraft was launched in late 2013 and it went into its observation orbit in early 2014, an orbit at Sun-Earth Lagrange point L2, about 1.5 million kilometers from the Earth away from the Sun. After some months of testing, it was commissioned in mid-2014.
It is the successor of a similar satellite, Hipparcos, which observed over 1989 - 1993. It was intended to go into a geostationary orbit, like a communications satellite, but its "apogee kick" rocket engine failed to fire, and the spacecraft was stuck in a geostationary transfer orbit, with its closest point about 500 km above the Earth's surface. But it still performed very well.
Parallax? As the Earth orbits the Sun, a star's apparent position goes in a sort of reflected projection of our planet's orbit, and the angular size of that projection is the parallax angle. One finds the distance to each star from (Earth's orbit size) / (parallax angle). Astronomers like to use the parsec ("parallax second") as a unit of distance for interstellar and larger distances, with 1 second of parallax giving 1 parsec of distance.
Proper motion? That's the angular velocity of a star across the celestial sphere. It is useful for finding what population a star is in, and also for some sorts of distance measurements.
The first successful measurements of parallax were done in the 1830's, and ground-based observations can do something like 0.01". For an uncertainty of 10%, this means a distance of 10 parsecs. Hipparcos could go to 100 parsecs, and Gaia to 10,000 parsecs, around the distance to our Galaxy's center.
The Gaia team will continue to work on their huge harvest of data from their spacecraft. They released Data Release 1 (DR1) on 2016 Sep 14, two years into the mission, DR2 on 2018 Apr 25, EDR3 ("Early") on 2020 Dec 3, and DR3 on 2022 Jun 13. Two more data releases are being worked on, DR4 at the end of this year, with data from the first five years, or later, and DR5 on 2030 or later, with all the data collected by the spacecraft.
The Gaia spacecraft collected data on the luminosities of stars, enabling some tracking of variable-star variations, and also a lot of radial velocities. From its astrometry came data on the relative motions of stars in multiple systems, including some with black-hole companions.
The spacecraft:
The spacecraft was launched in late 2013 and it went into its observation orbit in early 2014, an orbit at Sun-Earth Lagrange point L2, about 1.5 million kilometers from the Earth away from the Sun. After some months of testing, it was commissioned in mid-2014.
It is the successor of a similar satellite, Hipparcos, which observed over 1989 - 1993. It was intended to go into a geostationary orbit, like a communications satellite, but its "apogee kick" rocket engine failed to fire, and the spacecraft was stuck in a geostationary transfer orbit, with its closest point about 500 km above the Earth's surface. But it still performed very well.
- Hipparcos observed 100,000 stars with a precision of 0.001" - 1 milli-arcsecond
- Gaia observed 1,000,000,000 stars with the brighter ones having a precision of 0.00001" - 10 micro-arcseconds
Parallax? As the Earth orbits the Sun, a star's apparent position goes in a sort of reflected projection of our planet's orbit, and the angular size of that projection is the parallax angle. One finds the distance to each star from (Earth's orbit size) / (parallax angle). Astronomers like to use the parsec ("parallax second") as a unit of distance for interstellar and larger distances, with 1 second of parallax giving 1 parsec of distance.
Proper motion? That's the angular velocity of a star across the celestial sphere. It is useful for finding what population a star is in, and also for some sorts of distance measurements.
The first successful measurements of parallax were done in the 1830's, and ground-based observations can do something like 0.01". For an uncertainty of 10%, this means a distance of 10 parsecs. Hipparcos could go to 100 parsecs, and Gaia to 10,000 parsecs, around the distance to our Galaxy's center.
The Gaia team will continue to work on their huge harvest of data from their spacecraft. They released Data Release 1 (DR1) on 2016 Sep 14, two years into the mission, DR2 on 2018 Apr 25, EDR3 ("Early") on 2020 Dec 3, and DR3 on 2022 Jun 13. Two more data releases are being worked on, DR4 at the end of this year, with data from the first five years, or later, and DR5 on 2030 or later, with all the data collected by the spacecraft.
The Gaia spacecraft collected data on the luminosities of stars, enabling some tracking of variable-star variations, and also a lot of radial velocities. From its astrometry came data on the relative motions of stars in multiple systems, including some with black-hole companions.
The spacecraft:
Gaia (spacecraft) -- launch 2013 Dec 19 - in orbit 2014 Jan 8 - start obs 2014 Jul 25 - end 2025 Mar 27 -- COSMOS ESA Gaia Science Community - Gaia - Cosmos -- ESA - Gaia operations -- Gaia Archive -- ESA - Gaia - Archive- Hipparcos -- 1989 Aug 8 - 1993 Aug -- ESA Science & Technology - Hipparcos
