Astronomy Picture of the Day

Powers of Ten movie

Apparent Motions in the Sky

South Celestial Pole
Solar Eclipse
Lunar Eclipse
Earth's tilt, seasons, equinoxes and solstices
Retrograde Motion of Mars
Retrograde Motion Schematic in the Ptolemeic System
Retrograde Motion Schematic in the Copernican System
Phases of the Moon (animated)
Phases of Venus
"Earth Rise"
Kepler's unsuccessful Solar System model with Platonic Solids
Tycho Brahe and Johannes Kepler
Sir Isaac Newton
Escape Velocity
A schematic of Ocean tides
Ocean tides animation -- I
Ocean tides animation -- II
Rotating Moon, from Lunar Reconnaissance Orbiter

Light and Telescopes

EM Spectrum of radiation
Propagating Electro-Magnatic radiation
Example of an X-ray image
Pictures taken with an Infra-Red camera
Waves: transverse and longitudinal
Einstein's Nobel Prize
Electronic energy levels and transitions in a Hydrogen atom
Periodic Table of Elements and their Spectral lines
Three types of spectra: continuous (example: thermal), absorption, emission
Doppler Bumper Sticker
Doppler Effect applet
Diffraction applet -- I
Diffraction applet -- II
Blackbody, or Thermal Radiation Spectrum
Breaking the sound speed - a picture of the sonic boom
Explanation of Optics, and Pictures of Telescopes (prof. J. Dickey)
Large Binocular Telescope -- one of the two mirrors
Gemini optical telescope
Night Sky
Arecibo Radio Observatory, largest single dish

Formation of the Solar System --- Examples of Protoplanetary Systems

A portrait of Solar System planets (distances NOT to scale)
Solar System: planet distances to scale
Artist's conception of the Solar System during formation
Stages in the formation of the Solar System
The astronomers' Periodic Table of Elements
Orion star forming region in the Milky way Galaxy
Horsehead Nebula, a Star forming region
Eagle Nebula, a Star forming region
Protoplanetary Disks in Orion Nebula
A close-up of some Protoplanetary Disks
A Schematic View of Protoplanetary Disks in a Star Forming Region
Formation of Earth's Moon
Kepler telescope and its Earth trailing orbit around the Sun
Kepler telescope field of view
Extrasolar Planets

Earth, and the terrestrial planets

The Inner Planets
Venus, with and without the cloud cover
Map of the Earth
Pangaea: Fossils across continents
Plate Tectonics animation (UArizona site)
Plate Tectonics animation (Caltech site)
Greenhouse effect
Earth's Greenhouse effect
Atmospheric CO2 levels over Earth's history
Gullies on Mars
Gullies and Channels on Mars
Dust devil on Mars
Inclination of planets' axes of rotation

Jovian planets

Planets' Interiors
Jupiter's Great Red Spot
Jupiter's Galilean satellites
Io, Jupiter's moon, in true color
Volcanic eruption in progress on Io
Volcanic eruptions and its plume, on Io
Callisto, Jupiter's moon
Saturn's rings
Uranus
Neptune
Kirkwood gaps in the Asteroid Belt and here
Other examples of resonance: Child on a swing and Tacoma Narrows Bridge

Cratering in the Solar System

Asteroid Belt
Kuiper Belt and the Oort Cloud
Comet Tails
Pieces of comet Shoemaker-Levy 9
Comet Shoemaker-Levy 9 swallowed by Jupiter
Crater Chain on Ganymede
Impact crater on Mimas
Meteor Crater in Arizona

The Sun

Neutrino Detector, Sudbury, Ontario, Canada
History of neutrino discovery
More interesting information about neutrinos
Tokamak nuclear fusion reactor
Sun's photosphere
Solar Spectrum
Electronic energy levels of the Hydrogen atom
Sun's image in Hydrogen-alpha emission lines
National Solar Observatory, Sunspot, New Mexico and directions
Solar Corona seen during Solar eclipse
A close-up of a sunspot
Solar cycle (1995-present)
Solar cycle (1880-2000)
Sunspots at max and min of Solar Cycle
Doppler Image of Sun's rotation
Sun's tangled magnetic field
Solar prominence of Jan 17-18 2000, animation
Sun at Extreme UV wavelengths - short animations
Solar granulation
Solar 5-minute oscillations
Another mode of Solar oscillations

Stars

Stars
Absorption line spectrum superimposed on a thermal (blackbody) continuous spectrum
Spectral classification of stars
Eclipsing binary star system view 1 and view 2
HR diagram and with radii and with names of well known stars
Evolution of stars on the HR diagram - evolutionary tracks
Evolution of stars on the HR diagram - animation
Evolution of stars on the HR diagram - a schematic
Evolution of stars on the HR diagram - ...
Open and globular star clusters in the Andromeda galaxy
Globular star cluster M15
Planetary Nebulae
Planetary Nebulae (APOD)
Binding energy per nucleon: fusion vs. fission
A Spiral Galaxy with a Supernova on the edge
Supernova 1987A, in the Large Magellanic Cloud Galaxy (optical) and in X-rays and optical
Supernova Remnant (Tycho's)
Supernova Remnant (Crab Nebula)
Supernova Remnants
Binary Star System with an Accretion Disk
Periodic Table of Elements
Schematic of a pulsar
Schematic of an X-ray binary
Tests of the Theory of Relativity:
Time dilation, GPS system, Mercury's orbit Frame dragging (Gravity Probe B)
Artist's rendition of a Black Hole

Milky Way Galaxy

Schematic of Milly Way structure
Spiral galaxy M51
The Trifid Nebula
Reflection Nebula in Orion
The Pleiades Star Cluster, and its Reflection Nebula
The Eagle Nebula
Hydrogen Gas in the Milky Way Galaxy
A Map of the Milky Way's spiral structure
Interstellar Dust Grains
Interplanetary Dust Grains
Andromeda Galaxy in the UV
A Spiral Galaxy in different colors
Spiral arms animation
Galactic Center in the optical
Galactic Center in the Infra-Red
Galactic Center at Radio Wavelengths
Galactic Center: the very center
Galactic Center: stars orbiting the center and here

Galaxies

Dark Matter, Dark Energy and Cosmology