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"Armillary Sphere, an instrument used in astronomy. In its simplest form, consisting of a ring fixed in the plane of the equator, the armilla is one of the most ancient of astronomical instruments. Slightly developed, it was crossed by another ring fixed in the plane of the meridian." — The Encyclopedia Britannica, 1910

Armilla

"Armillary Sphere, an instrument used in astronomy. In its simplest form, consisting of a ring fixed…

"Sir Francis Drake's Astrolabe; an obsolete astronomical instrument of different forms, used for taking the altitude of the sun or stars, and for the solution of other problems in astronomy. "-Whitney, 1902.

Astrolabe

"Sir Francis Drake's Astrolabe; an obsolete astronomical instrument of different forms, used for taking…

A historical astronomical instrument used to predict positions of the Sun, Moon, planets and stars.

Later Astrolabe

A historical astronomical instrument used to predict positions of the Sun, Moon, planets and stars.

A historical astronomical instrument used to predict positions of the Sun, Moon, planets and stars.

Regiomontanus' Astrolabe

A historical astronomical instrument used to predict positions of the Sun, Moon, planets and stars.

An improvement upon the jackstaff from Davis, the Arctic navigator.

Backstaff

An improvement upon the jackstaff from Davis, the Arctic navigator.

Astronomer

Tycho Brache

Astronomer

Constellation: Cassiopeia

Cassiopeia

Constellation: Cassiopeia

During new and full moon, the earth, moon, and sun are all in the same straight line, but, that during the first and last quarters, they are at right angles. The portions of the earth and moon turned toward the sun are illumined, the shaded portions are in the darkness. To an observer on the earth, the moon, at <em>a</em>, appears new, since the dark part is turned toward the person; at <em>b</em>, however, it must appear full, since the illumined portions are toward the person. At <em>c</em>, and <em>d</em>, the positions of the quarters, only one-half of the illumined half, or one quarter, is seen.

Cause of the Phases of the Moon

During new and full moon, the earth, moon, and sun are all in the same straight line, but, that during…

The North Star (Polaris) varies so slightly from the true north that we may, for practical purposes, consider it true north. The North Star is easily identified by the pointers of the "Big Dipper."

Astronomical Compass

The North Star (Polaris) varies so slightly from the true north that we may, for practical purposes,…

Instantaneous axis of two cones, each with angular velocity

Conic Motion

Instantaneous axis of two cones, each with angular velocity

Astronomer

Copernicus

Astronomer

Nicolaus Copernicus (February 19, 1473 - May 24, 1543) was the first astronomer to formulate a scientifically based heliocentric cosmology that displaced the Earth from the center of the universe. His epochal book, <em>De revolutionibus orbium coelestium</em> (On the Revolutions of the Celestial Spheres), is often regarded as the starting point of modern astronomy and the defining epiphany that began the Scientific Revolution.

Nicolaus Copernicus

Nicolaus Copernicus (February 19, 1473 - May 24, 1543) was the first astronomer to formulate a scientifically…

"The earth shown as it would be if its axis were perpendicular to the plane of the orbit." -Wiswell, 1913

Earth's Axis Perpendicular to Plane of Orbit

"The earth shown as it would be if its axis were perpendicular to the plane of the orbit." -Wiswell,…

"A quadrant, or one fourth of a circle. The oblique lines indicate various angles with the base. The heavy line indicates the inclination of the earth's axis as compared with the plane of its orbit, which is represented by the base." -Wiswell, 1913

Inclination of Earth's Axis

"A quadrant, or one fourth of a circle. The oblique lines indicate various angles with the base. The…

"Relative positions of the earth and the sun on March 21 (spring equinox) and September 21 (autumn equinox) as seen from the position occupied by the earth on June 21 (summer solstice). Rays of light and heat meet the earth vertically on the Equator, and the days and nights are everywhere of equal length." -Wiswell, 1913

Spring Equinox and Autumn Equinox

"Relative positions of the earth and the sun on March 21 (spring equinox) and September 21 (autumn equinox)…

"The ancient southern constellation of the River (Po or Padus)." -Whitney, 1911

Eridanus

"The ancient southern constellation of the River (Po or Padus)." -Whitney, 1911

Astronomer

Galileo

Astronomer

"A zodiacal constellation, giving its name to a sign of the zodiac, lying east of Taurus, on the other side of the Milky Way." -Whitney, 1911

Gemini

"A zodiacal constellation, giving its name to a sign of the zodiac, lying east of Taurus, on the other…

Constellation: Hercules

Hercules

Constellation: Hercules

Sir William Herschel, famous English astronomer

Sir William Herschel

Sir William Herschel, famous English astronomer

An instrument which could more readily adapt itself to the swaying of the observer's body in a sea-way, soon displaced in good measure the astrolabe on shipboard. It in several ways modified forms for a long time served mariners as a convenient help in ascertaining the altitude of the celestial bodies. Precisely when it was first introduced is not certain; but the earliest description of it which has been found is that of Werner in 1514.

Jackstaff

An instrument which could more readily adapt itself to the swaying of the observer's body in a sea-way,…

Astronomer

Kepler

Astronomer

Johannes Kepler (1571-1630) was a German mathematician, astronomer, and astrologer. A key figure in the 17th century scientific revolution, he is best known for his laws of planetary motion, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican Astronomy. These works also provided one of the foundations for Isaac Newton's theory of universal gravitation.

Johannes Kepler

Johannes Kepler (1571-1630) was a German mathematician, astronomer, and astrologer. A key figure in…

If the earth were uniformly covered with a layer of water, the passage of the moon over any place as at <em>a</em>, would cause the water to lose its globular form, become bulged at <em>a</em>, and <em>b</em>, and flattened at <em>c</em>, and <em>d</em>. In other words, the water would become <em>deeper</em> at <em>a</em>, and <em>b</em>, at the parts of the earth nearest and farthest from the moon and <em>shallower</em> in all places 90 degrees or at right angles to these points.

Lunar Tide

If the earth were uniformly covered with a layer of water, the passage of the moon over any place as…

Constellation: Man with the Serpent

Man with the Serpent

Constellation: Man with the Serpent

Telescopic view of the moon, 1901.

Moon

Telescopic view of the moon, 1901.

Moon.

Moon

Moon.

The phases of the moon.

Moon Phases

The phases of the moon.

(1835-1909) American astronomer and mathematician.

Simon Newcomb

(1835-1909) American astronomer and mathematician.

"Two stars in the Big Dipper opposite the handle indicate the direction toward the North Star, which, though not very bright, is the first very noticeable star in line." -Wiswell, 1913

Finding the North Star

"Two stars in the Big Dipper opposite the handle indicate the direction toward the North Star, which,…

"Observatory at Delhi."

Ancient Indian observatory

"Observatory at Delhi."

Constellation: Orion

Orion

Constellation: Orion

Constellation: Persues

Persues

Constellation: Persues

The flood tides are the highest, and the ebb tides are the lowest. These are called <em>spring tides</em>. They occur twice during every revolution of the moon-once at <em>full</em>, and once at <em>new</em> moon. When the sun and moon are 90 degrees apart, each produces a tide on the portion of the earth directly under it, diminishing somewhat produced by the other body. High tide, then, occurs under the moon, while the high tide caused by the sun, becomes by comparison, a low tide. Such tides are called <em>neap tides</em>.

Positions

The flood tides are the highest, and the ebb tides are the lowest. These are called spring tides.…

(1837-1888) English astronomer

Richard A. Proctor

(1837-1888) English astronomer

Claudius Ptolemaeus, known as Ptolemy, was an ancient geographer, astrologer, and astronomer.

Ptolemy (Claudius Ptolemaeus)

Claudius Ptolemaeus, known as Ptolemy, was an ancient geographer, astrologer, and astronomer.

Claudius Ptolemaeus, known as Ptolemy, was an ancient geographer, astrologer, and astronomer.

Ptolemy Holding a Document

Claudius Ptolemaeus, known as Ptolemy, was an ancient geographer, astrologer, and astronomer.

(1477-1547) Famous German astronomer and cartographer.

Johannes Schoner

(1477-1547) Famous German astronomer and cartographer.

"The constellation which is prominent in early summer in the skies of the southern United States (where the whole of the magnificent tail clears the horizon), contains the first magnitude red star Antares and several of the second magnitude. With the Chaldeans and Greeks is extended over one sixth of the planetary circle, the scorpion being represented with exaggerated claw embracing a circular space where Libra is now placed." &mdash;Whitney, 1889

The Scorpio Constellation, with Libra

"The constellation which is prominent in early summer in the skies of the southern United States (where…

"Relative positions of the earth and the sun during the spring equinox, the summer solstice, the autumn equinox, and the winter solstice." -Wiswell, 1913

Seasons from Earth's Orbit

"Relative positions of the earth and the sun during the spring equinox, the summer solstice, the autumn…

"One standing at O will only see the half of the Sky which is above the circle NESW. The whole sky will seem to be turning about the line POP'; the Stars will seem to be moving along the paths EQW, BAB', etc. Stars so near the North Pole that they are inside the dark area KPN will never set."&mdash;The Foundation Library, 1911

The Sphere of the Sky

"One standing at O will only see the half of the Sky which is above the circle NESW. The whole sky will…

"Relative positions of the earth and the sun on June 21, the summer solstice. Summer and long days north of the Equator; winter and short days south of it." -Wiswell, 1913

Summer Solstice

"Relative positions of the earth and the sun on June 21, the summer solstice. Summer and long days north…

"Relative positions of the earth and the sun on December 21, the winter solstice. Winter and short days north of the Equator; summer and long days south of it. 1, North Frigid Zone; 2, North Temperate Zone; 3, Torrid Zone; 4, South Temperate Zone; 5, South Frigid Zone." -Wiswell, 1913

Winter Solstice

"Relative positions of the earth and the sun on December 21, the winter solstice. Winter and short days…

An optical instrument employed in viewing distant objects, as the heavenly bodies.

Telescope

An optical instrument employed in viewing distant objects, as the heavenly bodies.

"A telescope is an instrument designed for the observation of distant objects, and consists essentially of an objective for the formation of an image of the object and of an eyepiece for magnifying this image." &mdash; Avery, 1895

Telescope

"A telescope is an instrument designed for the observation of distant objects, and consists essentially…

"These telescopes were all reflectors; that is, instead of looking up at a star through a tube with a glass in the upper end [Herschel] would look down into the tube away from the star and see its reflecting in a concave mirror at the lower end of the tube."&mdash;The Foundation Library, 1911

A Great Reflecting Telescope

"These telescopes were all reflectors; that is, instead of looking up at a star through a tube with…

"The Galilean telescope has a double-concave eye-lens that intercepts the rays before they reach the focus of the objective." — Avery, 1895

Galilean Telescope

"The Galilean telescope has a double-concave eye-lens that intercepts the rays before they reach the…

"The reflecting telescope has an objective a concave mirror, tecnically called a speculum. The images formed by the speculum are brought to the eyepiece in several different ways. Sometimes the eyepiece consists of a series of convex lenses placed in a horizontal tube." — Avery, 1895

Reflecting Telescope

"The reflecting telescope has an objective a concave mirror, tecnically called a speculum. The images…

"The spy-glass or terrestrial telescope avoids the inversion of the image by the interposition of two double-convex lenses, m and n, between the objective and eyepiece. The rays diverging from the inverted image at I cross between m and n, and form an erect magnified, virtual image at ab." — Avery, 1895

Terrestrial Telescope

"The spy-glass or terrestrial telescope avoids the inversion of the image by the interposition of two…

Zenith telescope constructed at the International Stations at Berlin by Hermann Wanschaff.

Zenith Telescope

Zenith telescope constructed at the International Stations at Berlin by Hermann Wanschaff.

Constellation: The Crab

The Crab

Constellation: The Crab

Constellation: The Crow

The Crow

Constellation: The Crow

Constellation: The Dog

The Dog

Constellation: The Dog

Constellation: The Dragon

The Dragon

Constellation: The Dragon

Constellation: The Eagle

The Eagle

Constellation: The Eagle

Constellation: The Great Bear

The Great Bear

Constellation: The Great Bear

Constellation: The Hunter and Hounds

The Hunter and Hounds

Constellation: The Hunter and Hounds

Constellation: The Lion

The Lion

Constellation: The Lion

Constellation: The Lyre

The Lyre

Constellation: The Lyre

Constellation: The Scales

The Scales

Constellation: The Scales