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In this new Hubble Space Telescope view, the nebula appears in a new light, as seen in infrared wavelengths. The nebula, shadowy in optical light, appears transparent and ethereal when seen in the infrared, represented here with visible shades. The rich tapestry of the Horsehead Nebula pops out against the backdrop of Milky Way stars and distant galaxies that are easily seen in infrared light.
The Horsehead was photographed in celebration of the 23rd anniversary of the launch of Hubble aboard the space shuttle Discovery.
The backlit wisps along the Horsehead’s upper ridge are being illuminated by Sigma Orionis, a young five-star system just off the top of the Hubble image. A harsh ultraviolet glare from one of these bright stars is slowly evaporating the nebula. Along the nebula’s top ridge, two fledgling stars peek out from their now-exposed nurseries.
Gas clouds surrounding the Horsehead have already dissipated, but the tip of the jutting pillar contains a slightly higher density of hydrogen and helium, laced with dust. This casts a shadow that protects material behind it from being photo-evaporated, and a pillar structure forms. Astronomers estimate that the Horsehead formation has about five million years left before it too disintegrates.

Iapetus Spins and Tilts
Saturn’s two-faced moon tilts and rotates for Cassini in this mesmerizing movie sequence of images acquired during the spacecraft’s close encounter with Iapetus on November 12, 2005.The encounter begins with Cassini about 850,000 kilometers (530,000 miles) distant from Iapetus. Cassini approached over the moon’s northern hemisphere, allowing for excellent full views of a 575-kilometer (360-mile) wide impact basin in northeastern Cassini Regio. Astronomer Giovanni Cassini discovered the light/dark dichotomy of Iapetus’ two hemispheres (among his other Saturn discoveries), and the dark region – as well as the spacecraft – bears his name.Also prominent in these images is a 380-kilometer (235-mile) wide basin to the northwest of the larger basin, in the transition zone between Cassini Regio and a brighter region called Roncevaux Terra, with its 150-kilometer (95-mile) wide crater Roland (at top, with a prominent central peak).The movie takes Cassini to its closest approach, at about 415,000 kilometers (260,000 miles) from Iapetus, then looks back at the moon’s receding crescent. The sequence ends with Cassini at a distance of about 460,000 kilometers (285,000 miles) from the moon.Iapetus is 1,471 kilometers (914 miles) across.Images taken using ultraviolet, green and infrared spectral filters in the narrow-angle camera were combined to create false-color frames for this movie. The color seen here is similar to that produced in (red, green and blue) natural color views. Resolution in the original images taken at closest approach to Iapetus was about 3 kilometers (2 miles) per pixel. The color frames were resized to create the movie.
Credit: NASA/JPL/Space Science Institute

Jupiter’s moon Io, photographed by Voyager 2, 10 July 1979.
The end of this blog’s Io-thon follows on from yesterday’s post.  The photos used in this gif were taken with longer exposures than yesterday’s, so there is a better contrast between Io and the background.  Two volcanic eruptions are clearly visible in the top-left: I think that they are from Amirani and Maui.  There’s also an eruption on the right-hand side, but as its only lit by reflected light from Jupiter, it requires a lot of brightening to see (NASA’s photojournal shows it here).
You can also see a volcano in the south, tall enough to stay in sunlight even as the surrounding areas fall into darkness.
Yesterday I mentioned the bright spot glinting near the equator.  I asked Jason Perry (who used to write an Io blog) about it on Twitter and he said that it “looks like specular reflection off of glassy, cooled lava near Hi’iaka Patera.”  So there you go.

Jupiter’s moon Io, photographed by Voyager 2, 10 July 1979.
Voyager 2 wasn’t scheduled to fly closely past Io, but the discovery of active volcanoes by Voyager 1 led to Voyager 2 taking a long sequence of Io photos for the purposes of a volcano movie.  Part tree of this blog’s Io-thon is part of that movie: you can see one of the volcanic plumes just popping into view in the top-right.  I think that the volcano is Amirani, based on this discussion at the Gish Bar Times blog, but you probably shouldn’t trust me on Io geography.
Also interesting is that spot that starts to glint, almost directly below (as seen in the frames) that volcano, near the equator.  I don’t know what’s causing that: sunlight reflecting off lava?
Solar Flare, April 12th 2013, 22:00 UTC.
Solar flare, April 11th 2013, 08:30 UTC.
This flare is 200 000 kilometers wide, about half the distance between the Earth and the Moon.
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