User:Loooke/sandbox

Methods of detecting exoplanets
This is a list of ways to detect exoplanets. Exoplanets are planets that orbit other stars past the Sun. Scientists have found thousands of exoplanets.

However, exoplanets are very small and they do not give off visible light like stars. So, only a few exoplanets have been found directly. Most exoplanets have been found by looking at the changes they cause on their stars.

Confirmed methods
These are the methods that have worked at least once, to detect a planet for the first time or after it is found.

Astrometry
Astrometry is the science of measuring the position of a star in space over time. When planets move in orbits around stars due to the star's gravity, the star moves slightly due to the planet's gravity. So, a star with a planet orbiting it will "wobble" in a circle around the center of mass, and the star's position will keep changing.

Astrometry was first used for binary stars, and it is the oldest method to find exoplanets. For example, in 1943, the astronomer Kaj Strand announced that there was a planet orbiting 61 Cygni. A few more planets were claimed to be found, including several planets said to be around Lalande 21185. Scientists now know that these "planets" likely do not actually exist. This is because planets only cause a very small wobble on their stars, and the shifts in the stars' positions were too small to be detected by earlier telescopes.

Technology today is able to measure positions with more accuracy. A team using the Hubble Space Telescope could detect a planet around Gliese 876, but it was already discovered earlier. NASA's Exoplanet Archive lists one planet found using astrometry, named DENIS-P J082303.1-491201 b. Also, the Gaia spacecraft, which launched in 2013, can measure positions of stars to 10 millionths of an arcsecond, and may find tens of thousands of exoplanets.

Planetary nebulae to add
to List of planetary nebulae:


 * NGC 6445
 * NGC 6578
 * NGC 6818
 * NGC 6886
 * NGC 7026
 * NGC 7139
 * Pease 1