My imagination is that of an engineer with astronomy post-grad qualifications. What I see in the more typical image below is more akin to a caricature the classical illustration of a Dodo (Head to the right, feet to the bottom). In Steve’s image I see only exquisite detail including Bok Globules (top centre) and lanes of silhouetted dust.

Image credits:
S. Crouch, 2008. IC 2948, Running Chicken Nebula
M.Lorenzi and G.Favretto, 2003. IC2948 Complex

Needless to say, the image is not a simple happy snap of the planet and its moon. The NASA site carries a description of how the image was composed but it also carries quite a bit of jargon that I’ll try to decode here.
The camera responsible for the image, called LEISA, is sensitive to infrared light: the sort of light emitted by your TV remote. Light is characterised by its wavelength, with infrared light having a slightly longer wavelength than the nearby visible red light. The warmer an object is, the shorter the wavelength of the bulk of light it emits… if it is warm enough it glows visibly red, yellow, blue… think stars. While Jupiter’s atmosphere is not hot enough to emit much infrared light just because of its temperature it does reflect a lot of sunlight. Different gases reflect/absorb light at particular wavelengths and this can give away the atmospheric composition. By taking images in light of a range of wavelengths (1.59, 1.94, 1.85 micrometres) the camera is effectively taking images of gas of certain compositions, temperatures and, by inference, depths in the atmosphere. Using comparative information such as these images a great deal can be learnt about the object. The three images above show an approximate reproduction of the original images around the Great Red Spot (GRS). The imaging team shaded the images red, green, and blue and merged them to form the image of Jupiter.

The overlaid image of Io was constructed using a monochrome (black and white) optical photograph taken with the Long-Range Reconnaissance Imager (LORRI) camera. Using images from another camera, sensitive to bluish light typical of methane, an artificial colouring has been applied. Once more Tvashtar is billowing, and lava is flowing on the surface.

You can experiment with splitting light with a spectroscope by following the links from my previous Science Projects in a Small World post. The LEISA camera is tuned to pick up light from one narrow section of a full spectrum, similar to targeting the prominent lines in the image to the left.

You might recall the hubbub surrounding last year’s International Astronomical Union (IAU) decision to put a definition on the term planet. The fact that Eris was initially assessed as larger than Pluto (2390 km), and that there were likely to be many more objects like it, partly drove the need to define planet. Pluto, the last planet to be discovered, was relegated to the new category of dwarf planet to join the asteroid Ceres and Eris.

The ways that astronomers have found to gather information about things they cannot even hope to get close to never ceases to impress me.

Clear Skies!

See also:

[1] Brown, M. E.; Trujillo, C. A.; Rabinowitz, D. L. Discovery of a Planetary-sized Object in the Scattered Kuiper Belt. The Astrophysical Journal, Volume 635, Issue 1, pp. L97-L100. NASA ADS Entry

[2] Bertoldi, F.; Altenhoff, W.; Weiss, A.; Menten, K. M.; Thum, C. The trans-neptunian object UB313 is larger than Pluto. Nature, Volume 439, Issue 7076, pp. 563-564 (2006). NASA ADS Entry

[3] Brown, M. E.; Schaller, E. L.; Roe, H. G.; Rabinowitz, D. L.; Trujillo, C. A. Direct Measurement of the Size of 2003 UB313 from the Hubble Space Telescope. The Astrophysical Journal, Volume 643, Issue 1, pp. L61-L63. NASA ADS Entry

[4] Michael E. Brown and Emily L. Schaller. The Mass of Dwarf Planet Eris. Science, Vol. 316. no. 5831, p. 1585. Journal link

Clear Skies!

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Tvashtar in Motion

The unenhanced image can be seen to the right (click for larger version). In this image we can clearly see ring (annulus) of light around the planet’s edge caused by sunlight being refracted (bent) through the outermost atmospheric layers toward the camera. The ring system, Saturn’s most distinctive feature, is brightly lit and clearly visible beyond the extent of the planet. Where the rings pass in front of the planet they appear dark, obscuring the weak illumination of the planet’s dark side by light reflected from the rings. The broad, dark band in the rings is visible from Earth in modest amateur telescopes and is called the Cassini Division after its discoverer Giovanni Cassini. The Cassini division was thought to be a vacant gap between the A (outer) and B (inner) rings. Just inward from the very bright edge of the ring system (F ring, discovered 1979) is the Encke Gap named for Johann Encke. Near the planet’s lower left edge is a bright spike that hints at another ring, and below the planet is a faint blue streak that one could be forgiven for thinking was some kind of lens flare.

The image truly comes alive when the brightness levels are adjusted (left). The Cassini Division no longer looks like an abrupt break in the rings as more, faint, rings appear in the ‘gap’; their locations dictated by orbital resonance with Saturnian moons. The bright spike has resolved into a ring (G ring) discovered by the Voyager mission in 1980-1. The pale blue streak is fully illuminated, betraying its nature as a full ring (the E ring, discovered 1966). The character of the reflected light tells us that E ring differs from the majority of the rings; it consists of diffuse microscopic particles rather than larger lumps of ice and rock. The source of this material is thought to be volcanism on the Saturnian moon Enceladus which orbits within the haze. New rings, not easily visible in this scaled image were discovered by Cassini scientists in this image data (“Janus/Epimetheus” Ring between F and G, and “Pallene” Ring betwee G and E).

Spectacular as the image of Saturn is, the thing that really tugs on my sense of wonder is an almost insignificant dot called the Earth that makes an appearance just inside the G ring in the centre-right. At the time this image was taken Cassini-Huygens was about 2.2 million kilometres from Saturn and 1.5 billion kilometres from Earth. A similar image, in which the Moon can be seen as a bump on the side of Earth is here.

Read more about the Saturn ring system at Wikipedia.

Image Credit: NASA/JPL/Space Science Institute
PIA08329: In Saturn’s Shadow
PIA08324: Pale Blue Orb

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The outer circle of the image on the tee is marked in French with the twelve months of the year. Inside that ring is the inscription ‘Orbite ou route de la terre autour du soliel’ meaning something like ‘Orbit or road of the earth around the Sun’ (Soleil is the modern spelling). The other marking ‘Sytème de Ptolemée’ indicates that the diagram is of the Ptolemaic System (or geocentric system). The four circular symbols at March, June, September, and December depict the Earth, its equator, tropics and polar circles, and its orientation to the sun at this time.

The device in the middle is an armillary sphere (a term that escaped me on the night). The armillary does indeed have an astronomical purpose in that it is an abstract representation of the sky and the paths of objects in it, particularly the Sun. The armillary was developed by the Greeks around the third century BCE, and the Chinese around the first century BCE although simpler devices existed prior to this. The device can be used to make astronomical measurements of star positions, as the ancient Chinese, Greeks and Ptolemy did, or as a navigational aid. Many armillary spheres have a purely instructional purpose, demonstrating the relationship between various points, planes, and paths in identification of points in the sky. Armillaries are fairly common as purely ornamental objects.

In early armillary spheres the object at the centre represented the Earth because everybody knew the Earth was the centre of the Universe. Some later spheres depict the Sun at the centre after the Copernican view. The Earth is supported by a rod that forms the north-south axis of rotation and points to the north and south celestial poles. Surrounding the central object are a series of rings of various sizes and orientations and sometimes an object representing the Moon. The exact numbers of rings vary from device to device although the major ones are always present.

The rings can be divided into two groups; the great circles and others. There are typically five great circle rings:

• The projection of the Earth’s equator to form the celestial equator (Label A). This ring lies on a plane perpendicular to the axis through the Earth and is often marked with twenty-four divisions representing the hours of a day and used to identify the right ascension of an object. Right ascension is analogous to longitude on the Earth’s surface.
• The meridian ring (Label L), mounted on the top and bottom of the axis rod and crossing the equatorial ring at right angles. This ring is typically marked in degrees from zero at the equator through to 90 at the poles and is used to indicate the declination of a point in space. Declination is the astronomical equivalent of latitude on the Earth’s surface.
• The apparent path of the Sun through the sky over a year is represented by a ring (Label B) mounted at an angle of approximately 23 degrees to the equatorial ring. The angle comes from the tilt the Earth’s axis has. The ring is marked, often ornately, with twelve divisions representing the zodiacal constellations and its width may represent the range in which the Moon and classical planets wander in (23 plus/minus 9 degrees). This ring lies in a plane called the ecliptic plane. Aries is aligned with the intersection of the equatorial ring where this ring passes from the southern to northern hemisphere.
• The equinoctial colure (Label G) passes through the two poles and the intersection of the equatorial and ecliptic rings. Equinoctial means “equal night”, is related to the term equinox, and identifies the location of the Sun on two days when day and night are of equal length (roughly 20 March and 23 September).
• The solsticial colure (Label H) passes through the two poles and is perpendicular to the equinoctial colure. Its intersection with the ecliptic ring identifies the location of the Sun at its northern- or southernmost point in the sky during the year. These times are called the solstices and are approximately 21 June and 22 December. These are the longest and shortest daylight periods of the year.

Often a disc is present to represent the local horizon of the observer (Label M). The sphere can be mounted on a movable stand (as in the diagram) to allow it to be tilted and rotated for use at various latitudes and times.

Smaller rings are mounted to represent:

• The antarctic and arctic circles. These rings are parallel to the equator and approximately 23 degrees from the poles.
• The Tropic of Cancer approximately 23 degrees north of the equator and coincident with the northernmost excursion of the ecliptic. The name comes from the position of the Sun in the constellation Cancer at the June solstice… at least it was when the name was given. The Sun is now in Taurus at the June solstice because of the effect of precession.
• The Tropic of Capricorn approximately 23 degrees south of the equator and coincident with the southernmost excursion of the ecliptic. The naming rationale is similar to that for the Tropic of Cancer except for the December solstice (now Saggitarius).

The armillary sphere also makes a stylised appearance on the Portugese flag. Officially it symbolises the seafaring prowess of the Portuguese throughout history and particularly during the reign of King Manuel I (1495–1521) when Portugal was a major maritime leader. Astronomical observation and instruments like the armillary has a long history in navigation, particularly at sea where there are no landmarks. The sphere also features prominently in Portuguese Manueline architecture.

Want to build yourself an armillary sphere? Try here.

Clear skies!

The Antenna Galaxies get their name from their appearance in optical images taken from the ground. Visible on the left of image to the right (click for larger version) are two streams of stars that have been thrown out by gravitational interaction between the galaxies. From studies of the dynamics of the stars in these galaxies we believe that they started to interact something like 200-300 million years ago. The tails are the result of this initial interaction. The remnants of the original galaxy core regions are the two bright orange hued regions in the right hand pane of this image.

Despite the typical galaxy containing a billion or more stars it is very unlikely that the stars themselves would collide with each other: the average distance between stars being too large. The two galaxies interact with each other through gravitation resulting in disruption to established stellar motions. In the dense core regions of typical galaxies are large amounts of free gas and dust which will merge in the even of collision. Large brown lanes of dust, obscuring the light from the stars behind, are clearly visible around the image centre and running down the arm to the bottom of the image. In regions where the gas and dust reach high enough density we would expect to see a local peak in star formation. In the image to the left (click for large version) these star formation regions are numerous and appear as bluish clusters of hot, new stars surrounded by ionised hydrogen gas (pink glow).

I chose this image because it demonstrates the dynamics of galactic interaction and of star formation. It also gives a glimpse of the fate of our own galaxy should it ultimately it collide with the relatively nearby Andromeda Galaxy in a few billion years or so.

Images courtesy of NASA, Hubble Heritage and the STScI
News Release Number: STScI-1997-34
News Release Number: STScI-2006-46

The two Viking Mars missions each consisted of a lander and an orbiter. Using 102 images taken by the orbiters Jody Swann, Tammy Becker, and Alfred McEwen used the PICS(Planetary Image Cartography System) image processing system developed at the U.S. Geological Survey to produce this mosaic image. The mosaic images were reprojected and stitched together to give the effect of a global view from 2500 km altitude. The entire Valles Marineris system is visible. Also visible are three volcanoes, dark red spots on the west (left) edge, in the Tharsis region. These volcanoes also dwarf their terrestrial counterparts, rising about 25 kilometres above their surrounds.

You can take a video tour of the canyons at Google Video here. Other versions for download can be had here. Google Mars also provides views here.

Image courtesy NSDDC and NASA
NSDDC Mars Photos

The full image from September 2006 can be seen to the right (click for larger image). The current outburst of this star was first noticed by an Australian amateur astronomer, Nick Brown, on 6 January 2002. Nick was, as many amateurs do, surveying the sky photographically looking for novas and noticed a ‘new’ star on his images. At first the star seemed to be a typical nova but in mid-February it staged a massive 60-fold brightness increase, faded, and repeated to performance in March. It has been fading ever since.

The Hubble Telescope has imaged this area over time. The evolution of the illuminated area is highlighted in the image to the left. The bright dust clouds are seen because they reflect light that was emitted by the star’s outburst. The cloud appears to grow as the light moves progressively further from the star but the dust itself is not moving at any substantial pace; it was in-situ at the time of the outburst, perhaps ejected by the star at a much earlier stage. The effect is called a light echo in direct analogy to a sound echo rolling off objects at varying distances (think roll of thunder).

When professional astronomers identified the progenitor star as an F-class, 15.6 magnitude star with no history of variability the truly unique nature of V838 became apparent. This star has gone from a yellow star, a little heavier and hotter than the Sun, to a red giant in the space of a few months. Typically we would expect such a transition over periods of millions of years. There is certainly some good physics to explore here, and that’s why I find these images interesting.

Images courtesy of NASA, ESA and H.E. Bond (STScI)
STScI-2003-10
STScI-2006-50

There are two plumes in the full image (left, click for larger view).
The first and most obvious is the bluish cloud rising from the limb of the moon. The cloud protrudes about 140 km above the surface in a region called Pillan Patera (a caldera or volcanic depression).

The second volcanically active area is near the image centre and the boundary between light and dark. It is a light coloured circular feature with the shadow of the plume trailing away to the right (reddish shadow). This is the Prometheus plume, which has probably been active continuously since the Voyager images.

The discovery of volcanism on Io was entirely unexpected. A body as small as Io was expected to be dead and cold, having long since lost its internal heat to space. The diameter averages 3650 kilometres, but the moon is distorted from spherical by the gravitational effects of its close proximity to Jupiter. Just as the Moon raises tides on Earth, Jupiter raises tides in the body of Io. The kneading of the moon’s body causes heating which is probably the driver of the volcanism we see.

The colours present in the plumes and on the surface of Io are mainly due to the presence of large amounts of sulphur in the volcanic ejecta. Sulphur is ejected as 2-atom molecules of sulphur gas. After the gas settles near the surface and starts to cool it solidifies into 3- and 4-atom sulphur molecules giving a reddish hue. Slowly the molecules rearrange into a stable 8-atom ring that gives the familiar yellow colour of sulphur.

To me this image embodies the excitement of discovery of the completely unexpected. In 1977 nobody was seriously expecting to find volcanic activity among the icy outer bodies of the solar system; yet here they are. Voyager also discovered examples of volcanism on Triton, a moon of Neptune. Our solar system continues to surprise us.

Image: Courtesy NASA/JPL-Caltech.
PIA01081: Color Mosaic and Active Volcanic Plumes on Io