The proper motion of a star is the measurement of its change in position in the sky over time after improper motions are accounted for. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth The improper motion of a Star refers to the change of its Coordinates on the sky not originating from the motion of the star itself as opposed to Proper motion This contrasts with radial velocity which is the time rate of change in distance toward or away from the viewer. Radial velocity is the Velocity of an object in the direction of the line of sight (i

Introduction

Over the course of centuries, stars appear to maintain nearly fixed positions with respect to each other, so that they form the same constellations over historical time. In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture Ursa Major, for example, looks nearly the same now as it did hundreds of years ago. Ursa Major ( is a Constellation visible throughout the year in most of the northern hemisphere However, precise long-term observations show that the constellations change shape, albeit very slowly, and that each star has an independent motion. In Physics, motion means a constant change in the location of a body

This motion is caused by the true movement of the stars relative to the Sun and solar system through space. The Sun (Sol is the Star at the center of the Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. It is measured by two quantities: the proper motion angle and the proper motion itself. The first quantity indicates the direction of the proper motion on the celestial sphere (with 0 degrees meaning the motion due north, 90 degrees due east, and so on), and the second quantity gives the motion's magnitude, in seconds of arc per year. In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius " A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree.

Proper motion may also be given by the angular components in the right ascension (μ_α) and declination (μ_δ). Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either The net proper motion (μ) is given by:^[1]

where δ is the declination. The proper motion angle (θ) is related to these components by:[1]

Barnard's Star, showing position every 5 years 1985–2005.

Barnard's star has the largest proper motion of all stars, moving at 10. Barnard's Star ( is a very low-mass Red dwarf Star approximately 6 Light-years away in the Constellation of Ophiuchus (the 3 seconds of arc per year. Large proper motion is usually a strong indication that a star is relatively close to the Sun. The Sun (Sol is the Star at the center of the Solar System. This is indeed the case for Barnard's Star which, at a distance of about 6 light-years, is, after the Sun and the Alpha Centauri system, the nearest known star to Earth (yet, being a red dwarf, too faint to see without a telescope or powerful binoculars, with an apparent magnitude of 9. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by Alpha Centauri (α Centauri / α Cen also known as Rigil Kentaurus, Rigil Kent, or Toliman, is the brightest Star in the southern Constellation This list of stars nearest to the Earth is ordered by increasing distance out to a maximum of 5 Parsecs (16 According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool Star, of the Main sequence, either late K A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 54).

In 1992, Rho Aquilae became the first star to have its name invalidated by moving to a neighbouring constellation - it is now a star of the constellation Delphinus^[2]. Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar) Rho Aquilae (ρ Aql / ρ Aquilae is a Star in the Constellation Delphinus - it moved across the border from Aquila into Delphinus Delphinus (dɛlˈfaɪnəs Dolphin) is a rather small (ranked 69th northern Constellation very close to the Celestial equator. This will next happen to Gamma Caeli, which is due to become a star of the constellation Columba in the year 2400^[3]. Columba (kəˈlʌmbə Dove) is a small constellation just south of Canis Major and Lepus. The 24th century of the Anno Domini ( common) era will span the years 2301&ndash2400 of the Gregorian calendar.

A proper motion of 1 arcsec per year at a distance of 1 light-year corresponds to a relative transverse speed of 1. 45 km/s. For Barnard's star this works out to 90 km/s; including the radial velocity of 111 km/s (which is at right angles to the transverse velocity) gives a true motion of 142 km/s. True or absolute motion is more difficult to measure than the proper motion, as the true transverse velocity involves the product of the proper motion times the distance; that is, true velocity measurements depend on distance measurements, which are difficult in general. Currently, the nearby star with the largest true velocity (relative to the Sun) is Wolf 424 which moves at 555 km/s.

Usefulness in Astronomy

Stars with large proper motions tend to be nearby; most stars are far enough away that their proper motions are very small, of order a few thousandths of an arcsecond per year. It is possible to construct nearly complete samples of high proper motion stars by comparing photographic sky survey images taken many years apart. The Palomar Sky Survey is one source of such images. The National Geographic Society - Palomar Observatory Sky Survey (NGS-POSS is a major photographic survey of the night sky completed at Palomar Observatory in 1958 In the past, searches for high proper motion objects were undertaken using blink comparators to examine the images by eye, but modern efforts use techniques such as image differencing to automatically search through digitized image data. A blink comparator was a viewing apparatus used by Astronomers to find differences between two photographs of the night sky shot using Optical telescopes Image differencing is an Image processing technique used to determine changes between images Because the selection biases of the resulting high proper motion samples are well-understood and well-quantified, it is possible to use them to construct an unbiased census of the nearby stellar population -- how many stars exist of each true brightness, for example. Selection bias is a distortion of evidence or data that arises from the way that the data are collected Studies of this kind show that the local population of stars consists largely of intrinsically faint, inconspicuous stars such as red dwarfs. According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool Star, of the Main sequence, either late K

History

Proper motion was discovered in 1718 by Edmund Halley, who noticed that Sirius, Arcturus and Aldebaran were over half a degree away from the positions charted by the ancient Greek astronomer Hipparchus roughly 1850 years earlier. Edmond Halley FRS (ˈɛdmənd ˈhɔːlɪ ( November 8, 1656 &ndash January 14, 1742) was an English Astronomer Sirius is the brightest star in the night sky with a visual Apparent magnitude of &minus1 |- bgcolor="#FFFAFA"| note (category variability || H and K emission vary Aldebaran ( α Tau α Tauri Alpha Tauri is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky Hipparchus ( Greek; ca 190 BC &ndash ca 120 BC was a Greek Astronomer, Geographer, and Mathematician of the Hellenistic

In research published in 2005, the first measurement of the proper motion of a galaxy (the Triangulum Galaxy) was made. The Triangulum Galaxy (also known as Messier 33 or NGC 598) is a Spiral galaxy approximately 3 million light-years away in the ^[4]

Stars with high proper motion

The following are the stars with highest proper motion from the Hipparcos catalog. Hipparcos (an Acronym for Hi gh P recision Par allax Co llecting S atellite) was an Astrometry mission ^[5] It does not include stars such as Teegarden's star which are too faint for that catalog. Teegarden's Star, also known as SO0253005+165258, is a Star in the Constellation Aries which was found in 2003 to have a very large

Software

There are a number software products that allow a person to view the proper motion of stars over differing time scales. Two free ones are:

• Moovastar^[7] - Freeware - Windows, Fairly Basic. You can choose a region of the sky, set the limiting magnitude and set a time sequence (time step, number of steps, and step interval). The program will simulate the motion of the stars. There's a clear help function included.
• HippLiner^[8] - Freeware - Windows, Moderately sophisticated, with some pretty displays. Still under development, needs some more navigation and configuration features.

References

1. ^ ^{a b} Majewski, Steven R. (2006). Stellar Motions. University of Virginia. Retrieved on 2007-05-14. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1264 - Battle of Lewes: Henry III of England is captured in France making Simon de Montfort the
2. ^ Book-Review - Sky Catalogue 2000.0 - V.1 - Stars to Magnitude 8.0 ED.2 (1992). Retrieved on 2008-05-16. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1204 - Baldwin IX Count of Flanders is crowned as the first Emperor of the Latin Empire.
3. ^ Hamilton Amateur Astronomers (1996). Retrieved on 2008-05-16. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1204 - Baldwin IX Count of Flanders is crowned as the first Emperor of the Latin Empire.
4. ^ McKee, Maggie. "Distant galaxy's subtle sidling measured", New Scientist, March 3, 2005. Retrieved on 2007-07-21. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 356 BC - Herostratus sets fire to the Temple of Artemis in Ephesus, one of the Seven Wonders of the World  
5. ^ Staff (September 15, 2003). The 150 Stars in the Hipparcos Catalogue with Largest Proper Motion. ESA. Retrieved on 2007-07-21. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 356 BC - Herostratus sets fire to the Temple of Artemis in Ephesus, one of the Seven Wonders of the World
6. ^ SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved on 2007-07-21. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 356 BC - Herostratus sets fire to the Temple of Artemis in Ephesus, one of the Seven Wonders of the World
7. ^ http://www.xs4all.nl/~sahjps/astro.html
8. ^ HippLiner - A 3D interstellar spaceship simulator with constellation writing function

See also the article on the Solar apex

External links

• Hipparcos: High Proper Motion Stars
• Edmond Halley: Discovery of proper motions