Stars and ConstellationsPhysics 113 Goderya

Chapter(s): 2Learning Outcome:

Constellations

In ancient times, constellations only referred to the brightest stars that appeared to form

groups, representing mythological figures.

Finding objects in the sky

• Constellations

Source: Jodrell Bank Observatory

Finding objects in the sky

• Orion Nebula

Source: Jodrell Bank Observatory

Constellations (2)

Today, constellations are well-defined regions on the sky, irrespective of the presence or absence of bright stars in those regions.

Apparent viewThe stars of a constellation only appear to be close to one another

Usually, this is only a projection effect.

The stars of a constellation may be located at very different distances from us.

Star NamesStars are named by a Greek letter () according to their relative brightness within a given constellation + the possessive form of the name of the constellation:

OrionBetelgeuze

Rigel

Betelgeuse = OrionisRigel = Orionis

Circumpolar Constellations

Non Circumpolar Constellations

Constellation of the ZodiacDue to Earth’s revolution around the sun, the sun appears to move through the zodiacal constellations.

Constellations from Different Places

(SLIDESHOW MODE ONLY)

Stellariumhttp://www.stellarium.org

Go download it if you have a computer at home. Its Free

Source: Jodrell Bank Observatory Screen from STELLARIUM (A freeware software)

Angles in Astronomy

• Angles– Circle = 360º =2π radians– Two Perpendicular lines = 90º– 1º = 60 ‘ (arc minutes)– 1‘ = 60 " (arc seconds)– 1 radian = 360x60x60/2π = 206265 "– Sun & Moon Diameter = 0.5º = 30 “– Extended fist = 5º

Angles in Astronomy

Small Angle Formula

distance

diameterlinear

5206,26

diameterangular

km 384,000

km 3476

5206,26

diameterangular

5.06060

18700187diameterangular

Example for Moon