Stars and the Solar System

Appearance (Phases) of the Moon during a month

Phases of the Moon S U N R A Y SS U N R A Y S New Full First Quarter Third Quarter Waxing Crescent Waxing Gibbous Waning Crescent Waning Gibbous Earth

Notice the position of Mars, Saturn and Venus with respect to the nearby stars

A month later, planets have drifted to the east among stars which drift from east to west

Motion of planets towards east among stars is clearly seen

A month later, the sky map shows clearly that the planets move among the stars

Retrograde Mars apod.nasa.gov/apod/ap html Credit & Copyright: Tunc Tezel apod.nasa.gov/apod/ap htmlTunc Tezel Sun Earth Superior Planet Stars Notice how the changing position of the earth in its revolution round the sun and that of the planet causes the retrograde motion of the planet

Earth Moon Mercury Venus Sun Jupiter Mars Saturn Fixed Stars Realm of the Gods

Galileo discovered evidence to support Copernicus’ heliocentric theory when he observed four moons in orbit around Jupiter. Beginning on January 7, 1610, he mapped nightly the position of the 4 “Medicean stars” (later renamed the Galilean moons). Over time Galileo deduced that the “stars” were in fact moons in orbit around Jupiter. [Adapted from Galileo Galilei, 1610, Sidereus Nuncius (“The Starry Messenger.”)]

Possibly the most compelling argument Galileo made in favor of the Heliocentric Universe of Copernicus was based on the observations of Venus. Galileo observed the phases of Venus throughout the year. At times Venus presented a small but circular disk and at other times a large crescent. Based on these facts as illustrated in his drawings in Sidereus Nuncius, Galileo reasoned that Venus must orbit the Sun; proof of the Copernican Universe.

Orbits of the Three Inner Galilean Moons An animation of the three-way mean motion resonance that guarantees the stability of the Jovian system. Io orbits Jupiter in 1.77 days (about 43 hours). The next moon, Europa, completes an orbit in twice that period (3.55 days), while the third moon, Ganymede, completes an orbit in twice the period of Europa (7.15 days). In each case the orbital period defines the day/night cycle. All four Galilean moons always turn the same hemisphere to Jupiter because of tidal drag. Wikimedia image created 2006 by Splarka. TheNeighborhood /GalileanMoons.ht ml

Sun Venus Earth Phases of Venus 47 ° V E Sun Venus is always within an angle of 47° of the sun. That is why it is seen either just after sunset (evening ‘star’) or just before sunrise ( morning ‘star’).

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Solar System Not to Scale Venus Earth Saturn Jupiter Asteroids Mars Mercury Neptune SUN Uranus

Jupiter Mars Earth Venus Mercury Neptune Uranus Saturn Jupiter Inner Planets Outer Planets The Solar System Using just one scale it is difficult to show both the inner and the outer solar system in the same diagram. On the left is the complete solar system. On the right is the blow up of the inner solar system.

NASA Mercury Venus Earth Moon Mars Jupiter Saturn Uranus Neptune Asteroid (253) Mathilde, about 59 km x 47 km(253) Mathilde NASA Comet WestNASA Piece of a meteorite NASA

Pole Star All the stars belonging to a constellation are not at the same distance, as shown here for Ursa Major (Saptarishi)

NASA Constellation Orion, visible in winter

Constellation Leo, a zodiacal constellation

Source : ganymede.nmsu.edu/tharriso/ast110/class05.html Ecliptic Zodiac Belt There are 12 constellations (Rashis) in the Zodiac. The sun stays in each constellation for about a month. On 21 August the sun appears to be in Leo. On 21 July it is in Cancer. On 21 March it is in Pisces.

1 May :00 pm

1 May pm

2 May am

2 May am

1 May pm 1 May pm 2 May am 2 May am

Great Bear at six-hour interval during a night.

Star Trails in Northern Skies Credit and Copyright: David MalinDavid Malin

Star Trails In Southern Skies Credit: Photograph by David Malin Copyright: Anglo-Australian ObservatoryAnglo-Australian Observatory

Equator Axis of Rotation Earth Pole Star Ecliptic Plane 23.5°

(Northward Journey of the Sun) 23 Dec 21 JUN Uttaryan Dakshinayan Southward journey of the Sun

Ecliptic Equator Daily Motion of the Sun

E W N S 21 JUN 21 MAR, 23 SEP 23 DEC HORIZON CELESTIAL EQUATOR Annual and Daily Motion of the Sun

Moon’s Orbit Sun Earth Earth Shadow Total Lunar Eclipse Schematic diagram of lunar eclipse. The sizes of the sun, moon and the earth and distances between them are not to scale. When moon passes through the shadow of the earth, it is eclipsed.

Schematic diagram of solar eclipse. The sizes of the sun, moon and the earth and distances between them are not to scale. The shadow of the moon falling on the earth causes the solar eclipse. Sun Earth Moon Total Eclipse Partial Eclipse