Venus Transits and Saturn Rings

c.150 CE

Ptolemy calculated the distance between the Earth and the sun to be 1,210 times the radius of the Earth, or roughly 5 million miles (8 million km).

1619

Although the absolute values are unknown, Kepler's third law provides the ratio of planetary orbital sizes.

1610

Galileo announces the discovery of four moons orbiting Jupiter.

1631

The first known planetary transit is seen by French astronomer Pierre Gassendi as Mercury passes across the solar disk.

Pierre Gassendi

The first known planetary transit is seen by French astronomer ____ as Mercury passes across the solar disk.

1655

Titan, a moon orbiting Saturn that is 50% larger than the moon of Earth, is found by Christiaan Huygens.

Christiaan Huygens

Titan, a moon orbiting Saturn that is 50% larger than the moon of Earth, is found by ______>

1716

According to Edmond Halley, a precise timing of Venus's transit could result in a precise measurement of the Earth's distance from the sun.

1801

The first asteroid is located between Mars and Jupiter in its orbit.

1859

James Clerk Maxwell, a Scottish physicist demonstrates that Saturn's rings cannot be solid because they would disintegrate under the pull of gravity.

James Clerk Maxwell

a Scottish physicist demonstrates that Saturn's rings cannot be solid because they would disintegrate under the pull of gravity.

2012

The most recent Venus transit occurred; the next two will occur in 2117 and 2125.

Jeremiah Horrocks

In 1639, _____, a 20-year-old English astronomer, discovered inaccuracies in Kepler's tables, which led him to forecast Venus would cross the face of the sun.

William Crabtree

Horrocks wrote to his associate _____, urging him to observe the transit because it was only four weeks away.

helioscopes

Using ____, which focused the sun's image from a telescope onto a plane, Horrocks and Crabtree independently set up their systems on December 4, 1639.

December 4, 1639

Using helioscopes, which focused the sun's image from a telescope onto a plane, Horrocks and Crabtree independently set up their systems on _____.

Giovanni Cassini

an Italian astronomer working at the Panzano Observatory near Bologna, was given a cutting-edge refracting telescope by Rome's Guiseppe Campini in 1664.

Guiseppe Campini

Cassinis was given a cutting-edge refracting telescope by Rome's ______ in 1664.

Titan

He focused his telescope there on Saturn, whose largest moon, _____, had been found by Christiaan Huygens in 1655.

Iapetus and Rhea

In 1671 and 1672, Cassini found two more moons:

Tethys and Dione

In 1684, two more ephemeral satellites, _____, were found by him.