Astronomy Picture Of the Day (APOD)Comet Hale-Bopp Inbound
Headed toward the inner Solar System, the much anticipated Comet Hale-Bopp has promised to put on a big show next spring. The comet's apparent brightness is currently approaching 4th magnitude and its inbound journey has been closely followed by many observers.
A Sky Full Of Hydrogen
Interstellar space is filled with extremely tenuous clouds of gas which are mostly Hydrogen. The neutral hydrogen atom (HI in astronomer's shorthand) consists of 1 proton and 1 electron. The proton and electron spin like tops but can have only two orientations; spin axes parallel or anti-parallel.
Mercury, the closest planet to the Sun, remains the most mysterious of the Solar System's inner planets. Hiding in the Sun's glare it is a difficult target for Earth bound observers.
Nebula Nova Cygni Turns On
Old photographs show no evidence of the above nebula. In 1992, a white dwarf star in Cygnus blew off its outer layers in a classical nova explosion: an event called Nova Cygni 1992. Light flooded the local interstellar neighborhood, illuminated this existing gas cloud, excited the existing hydrogen, and hence caused the red emission.
Microlensing of the Einstein Cross
The famous "Einstein Cross" is a case where a single object is seen four times. Here a very distant QSO happened to be placed right behind a massive galaxy. The gravitational effect...
Our Solar System from Voyager
After taking spectacular pictures of our Solar System's outer planets, Voyager 1 looked back at six planets to take our Solar System's first family portrait. Here Venus, Earth, Jupiter, Saturn, Uranus, and Neptune, were all visible across the sky.
Disorder in Stephan's Quintet
Five closely grouped galaxies are visible in this image made using the Kitt Peak National Observatory 2.1 meter telescope. The grouping is commonly known as Stephan's Quintet. Four of the galaxies show essentially the same redshift suggesting that they are at the same distance from us.
The Milky Way Through the Summer Triangle
There are more than a few stars in our Galaxy. The light from many of them combines to appear as a wisp of faint light across the night sky - the Milky Way.
Starburst Ring in Galaxy NGC 1317
Where do stars form? A typical place is an area of dense nebular gas common to arms in spiral galaxies. Sometimes, however, a burst of star formation can occur with unusual geometry. Nearby galaxy NGC 1317 shows such an unusual ring of star formation surrounding its barred nucleus.
Comet Halley's Nucleus
Here is what a comet nucleus really looks like. For all active comets except Halley, it was only possible to see the surrounding opaque gas cloud called the coma. During Comet Halley's most...