German astronomer Johannes Kepler's conceptualization of the orbit of Mars. Kepler (1571-1630), devised the three fundamental laws of planetary motion. These laws were based on detailed observations of the planets made by Tycho Brahe and himself. Kepler's first law states that the planets orbit the Sun in elliptical paths, with the Sun at one focus of the ellipse. The second law states that the closer a planet comes to the Sun, the faster it moves. Kepler's third law states that the ratio of the cube of a planet's mean distance from the Sun to the square of its orbital period is a constant. Newton used these ideas to formulate his theory of gravity.

An illustration of a passage instrument, an astronomical tool used to determine the time stars pass through the local meridian. Knowing this allowed astronomers to determine the precise time and correct their observatory clocks. After 1913, the passage instrument was discarded in favor of a crystal radio-detector used for determining the drift of the observatory clocks.

Model of the orbit of the planets by Johannes Kepler, devised in 1596-97. German astronomer Kepler devised the three fundamental laws of planetary motion. These laws were based on detailed observations of the planets made by Tycho Brahe and himself. Kepler's first law states that the planets orbit the Sun in elliptical paths, with the Sun at one focus of the ellipse. The second law states that the closer a planet comes to the Sun, the faster it moves. Kepler's third law states that the ratio of the cube of a planet's mean distance from the Sun to the square of its orbital period is a constant. Newton used these ideas to formulate his theory of gravity.

A reflecting circle, used to measure longitude by calculating the distance between the moon and a nearby star. German astronomer Johann Tobias Mayer developed the device, which was improved upon by French physicist Jean-Charles Borda in the 1780s.

English astronomer William Lassell's 24-inch reflecting telescope, completed in 1845. Lassell's (1799-1880) telescope was the first to be mounted equatorially. With it, in 1851, he discovered four new satellites: Neptune, Neptune's largest moon, and two moons of Uranus.

A diagram of 1660 showing the sun-centred universe, an idea revived by Copernicus.

Illustration of sunspots from Galileo's 1613 book on the sun. Galileo Galilei (February 15, 1564 - January 8, 1642) was an Italian physicist, mathematician, astronomer and philosopher.

A transit instrument, used for precisely observing the positions of stars.

A universal instrument, which is a type of transit instrument, used for precisely observing the positions of stars. The universal instrument allows for transit measurements in any one direction.

Uraniborg, an astronomical observatory operated by Tycho Brahe in Denmark. Tycho Brahe (1546-1601) was a Danish astronomer. After becoming interested in astronomy as a student in Copenhagen, Tycho Brahe realized the difficulty of making accurate measurements of celestial bodies with the instruments of the day. His designs for new methods and devices won him great fame. He was granted an estate on the island of Hven to conduct his research, and funding to built the Uraniborg observatory. From there he generated the most accurate astronomical data of his time. He was exiled to Prague in 1597 and was assisted in his work there by Johannes Kepler until his death.

An historical astronomical instrument, the heliotropii telioscopici or helioscope, used for observing and following the sun's motion. The first one was designed by Christoph Scheiner (1575-1650) to help him observe sunspots. The instrument projects a telescopic image of the sun onto a white piece of paper in a dark room. Color enhancement of BM8770.

An illustration of an armillary sphere (also known as spherical astrolabe, armilla, or armil), which is a model of the celestial sphere. This woodcut is by Oronce Fine, mathematician and author of the Solaribus Horologiis, and was printed in Johannus de Sacrobosco's Textus de Sphaera in 1538. Color enhancement of BM8716.

Astronomical clock. Color enhancement of BN2256.

An illustration showing a person calculating the angle between Aldebaran (the brightest star in the constellation Taurus) and the moon, with respect to the ecliptic. Color enhancement of BN2259.

An illustration of the northern hemisphere of a brass celestial globe belonging to Major-General Sir John Malcolm. The brass globe was made by Muhammad ibn Hilal, possibly from Maragha, north-west Iran, AD 1275-76. Color enhancement of BN2295.

An illustration of the southern hemisphere of a brass celestial globe belonging to Major-General Sir John Malcolm. The brass globe was made by Muhammad ibn Hilal, possibly from Maragha, north-west Iran, AD 1275-76. Color enhancement of BN2296.

Korean world map, 17th-18th century.

Ancient map of Europe, North Africa and the Middle East.

An equatorial telescope, mounted so that it has two axes of motion at right angles to each other, one parallel to the axis of the earth. Color enhancement of BN2279.

An eighteenth century illustration of a celestial sphere, or rather a representation of the hemisphere of the heavens that can be seen from the northern half of Earth. The moveable horizon can be adjusted to represent the horizon of any observer, whether at the equator or the north pole, but it always cuts the ecliptic at 0 degrees Aries and 0 degrees Libra. Color enhancement of BN2269.