Data
Services

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The Sky This Week

Time and Date.com
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Rise/Set/Transit/
Twilight Data

Complete Sun and Moon Data for One Day

Table of Sunrise/Sunset, Moonrise/Moonset, or Twilight Times for an Entire Year

Rise/Set/Transit Times for Major Solar System Objects and Bright Stars

Duration of Daylight/Darkness Table for One Year

Phases
of the Moon

Dates of Primary Phases of the Moon

Fraction of the Moon Illuminated

What the Moon Looks Like Today

Eclipses
and Transits

Eclipses of the Sun and Moon

Solar Eclipse Computer
Computes circumstances for selected solar eclipses at any given location.

Lunar Eclipse Computer
Computes circumstances for selected lunar eclipses at any given location.

Recent and Upcoming Transits of Mercury and Venus

Transit Computer
Computes circumstances for selected transits of Mercury and Venus at any given location.


Positions of
Selected Celestial
Objects

Altitude and Azimuth of the Sun or Moon During One Day

Topocentric Configuration of Major Solar System Bodies
Provides tables of low precision topocentric position data for the Sun, Moon, and major planets.

Geocentric Positions of Major Solar System Objects and Bright Stars
Provides high precision geocentric position data for the Sun, Moon, major planets and selected bright stars.

Topocentric Positions of Major Solar System Objects and Bright Stars
Provides high precision topocentric position data for the Sun, Moon, major planets and selected bright stars.


Synthetic Views
of the Earth and
Solar System
Bodies

Day and Night Across the Earth
Creates synthetic views of the Earth's surface (in grayscale or color) for any date and time.

Apparent Disk of Solar System Object
Creates a synthetic image of the telescopic appearance of the Moon or other solar system object for specified date and time.


Dates

Earth's Seasons - Equinoxes, Solstices, Perihelion, and Aphelion 2000-2020

Spring Phenomena, 25 BCE to 38 CE

Julian Date Conversion

Celestial
Navigation

Celestial Navigation Data
Provides computed altitudes and azimuths and other data for an assumed position and time.

Navigational Star Chart

Miscellaneous

Astronomical Almanac Online
Provides complementary data to the printed Astronomical Almanac.

International Celestial Reference System (ICRS) - Important links relating to the implementation of the ICRS

Occultations of Stars by Asteroids

 

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Glossary of Terms

Astronomical Almanac Online Glossary

Phenomena of the Sun and Moon

Rise, Set, and Twilight Definitions

Lengths of Longest and Shortest Days

Length of Day and Night at the Equinoxes

The Dark Days of Winter

Visibility of the Crescent Moon

References on Eclipses

Phases of the Moon and Percent of the Moon Illuminated

Time

Universal Time and Greenwich Mean Time

Computing Greenwich Apparent Sidereal Time

What are the U.S. Time Zones?

World Time Zone Map

When Does Daylight Time Begin and End?

Calendars and Historical Events

Introduction to Calendars

Leap Years

U.S. Holidays

The International Date Line

The 21st Century and the 3rd Millennium

The First Sunrise of the New Millennium

Computing Astronomical Data and Phenomena

Converting Between Julian Dates and Gregorian Calendar Dates

Computing Times of Rise and Set

Approximate Solar Coordinates

Computing Greenwich Apparent Sidereal Time

Computing Altitude and Azimuth

Other Topics

Astronomical Data Used for Litigation

Celestial Navigation Resources

The Seasons and the Earth's Orbit

International Celestial Reference System (ICRS)

When Did the Asteroids Become Minor Planets?

Masses of the Largest Asteroids

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JAVA Applets

Juergen Giesen's
GeoAstro Applet Collection