Stars move300 years ago it was discovered that stars move relative to each other and the constellations slowly change their shapes.

The images to the left show Barnard's star, which has the largest proper motion of all stars. It moves by 10.4 arcseconds per year and its parallax amounts to 0.55 arcseconds. Can you spot the star in the photos to the left?

Sky&Telescope

The annual motion of the Earth relative to the Sun causes stars to follow a small elliptical path in the sky. The size of the ellipse (parallax angle) tells us about the distance to the star. The smaller the parallax, the further away is the star.

apparent motion, distant star

apparent motion, nearby star

position of Earth in January

position of Earth in July

Sun

1951 2013

70,000 years ago

25,000 years ago in 70,000 years

parallax angle

Sky&Telescope

With a small telescope one can recognize the fast motion of the star and its annual variation due to the motion of the Earth around the Sun within an observational period of one and a half years.

1 arcsecond

1996,0

54º

52º

50º

48º

46º

44º

42º

40º

38º

49.0 s 48.8 s 48.6 sright ascension 17h 57min

decl

inat

ion

+40º

40’

Apr 23

May 22

Jun 23 1994,5

Jul 22

Aug 24

Sep 20

Oct 23

Nov 23

1995,0

Mar 4

Mar 27Apr 12

May 7

Jun 6

Jun 18Jul 4 1995,5

Aug 8

Sep 7

Oct 10Nov 6

Dec 8

observations by D. di Cicco

motion of Barnard’s star

Parallaxes are very smallThe closest star has a parallax of only 0.74 arcseconds. A star near the centre of our Galaxy has a parallax of about 0.0001 arcseconds. In order to measure such small angles we need an instrument like Gaia.

Today80,000 arcseconds = 22 degrees

1 arcsecond

10 years of proper motion and parallax

The shape of Ursa Major throughout time

Parallax

The first credible parallax was

measured for the star 61 Cygni in

1838.

3

Content and design Universitat de Barcelona / ICC / IEEC; Adaptation and translation by ARI, ZAH, Heidelberg and Lohrmann Observatory, Dresden; Sponsored by MINECO-FEDER and DLR