Io: Moon over Jupiter

IoOverJupiter_Cassini

How big is Jupiter’s moon Io? The most volcanic body in the Solar System, Io (usually pronounced “EYE-oh”) is 3,600 kilometers in diameter, about the size of planet Earth’s single large natural satellite.

Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet’s relative size. Although in the featured picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter.

That puts Io nearly 350,000 kilometers above Jupiter’s cloud tops, roughly equivalent to the distance between Earth and Moon. In July, NASA’s Juno satellite began orbiting Jupiter and will sometimes swoop to within 5,000 kilometers of Jupiter’s cloud tops.

The Easterbunny Comes to NGC 4725

NGC 4725

At first called “Easterbunny” by its discovery team, officially named Makemake is the second brightest dwarf planet of the Kuiper belt. The icy world appears twice in this astronomical image, based on data taken on June 29 and 30 of the bright spiral galaxy NGC 4725.

Makemake is marked by short red lines, its position shifting across a homemade telescope’s field-of-view over two nights along a distant orbit. On those dates nearly coincident with the line-of-sight to the spiral galaxy in the constellation Coma Berenices, Makemake was about 52.5 astronomical units or 7.3 light-hours away. NGC 4725 is over 100,000 light-years across and 41 million light-years distant. Makemake is now known to have at least one moon. NGC 4725 is a famous one-armed spiral galaxy.

Perseid, Aurora, and Noctilucent Clouds

Perseid, Aurora, and Noctilucent Clouds
Perseid, Aurora, and Noctilucent Clouds

Night skies over northern Sweden can hold some tantalizing sights in August. Gazing toward the Big Dipper, this beautiful skyscape captures three of them in a single frame taken last August 12/13.

Though receding from northern skies for the season, night shining or noctilucent clouds are hanging just above the horizon. Extreme altitude icy condensations on meteoric dust, they were caught here just below an early apparition of a lovely green auroral band, also shining near the edge of space.

The flash of a Perseid meteor near the peak of the annual shower punctuates the scene. In fact, this year’s Perseid shower will peak in the coming days, offering a continuing chance for a night sky photographer’s hat trick.

Colliding Galaxies in Stephan’s Quintet

Colliding Galaxies
Colliding Galaxies

Will either of these galaxies survive? In what might be dubbed as a semi-final round in a galactic elimination tournament, the two spirals of NGC 7318 are colliding. The featured picture was created from images taken by the Hubble Space Telescope.

When galaxies crash into each other, many things may happen including gravitational distortion, gas condensing to produce new episodes of star formation, and ultimately the two galaxies combining into one. Since these two galaxies are part of Stephan’s Quintet, a final round of battling galaxies will likely occur over the next few billion years with the eventual result of many scattered stars and one large galaxy. Quite possibly, the remaining galaxy will not be easily identified with any of its initial galactic components.

Stephan’s Quintet was the first identified galaxy group, lies about 300 million light years away, and is visible through a moderately-sized telescope toward the constellation of the Winged Horse (Pegasus). Free Download: APOD 2017 Calendar: NASA Images