Earth and Space

Wednesday, December 28, 2011

Moving sand dunes

In several desert areas, the slow motion of sand dunes can be a challenge for modern human activities and a threat for the survival of ancient places or archaeological sites. However, several methods exist for surveying the dune fields and estimate their migration rate. Among these methods, the use of satellite images, in particular of those freely available on the World Wide Web, is a convenient resource for the planning of future human settlements and activities. More at http://arxiv.org/abs/1112.5572

The barchans move. Note the dunes on the tracks.

Thursday, October 27, 2011

Giant Waterworld Around Naked Eye Star

Giant Waterworld Confirmed Around Naked Eye Star - Technology Review
"55 Cancri A is a Sun-like star some 40 light years away. It has an apparent magnitude of about 6 and so is visible to the naked eye in the constellation of Cancer.
This star is unusual in that it is just one of a handful that are known to have at least 5 planets. The innermost of these planets--55 Cancri e--was discovered in 2004 and has since had plenty of attention from astronomers. Various groups have observed the the changes in radial velocity that it causes its parent star. This tells them about that it orbits its star every 18 hours and that its mass is about 8 times Earth's or about half Neptune's.""The innermost planet around 55 Cancri A is almost certainly an exotic waterworld with a radius about twice Earth's, say astronomers"

Friday, October 7, 2011

Eta Carinae's Homunculus

Homunculus Nebula is surrounding the star system Eta Carinae. The nebula is embedded within a much larger ionized hydrogen region, which is the Carina Nebula. Homunculus is believed to have been ejected in a huge outburst from Eta Carinae in 1841, so brightly to be visible from Earth. This massive explosion produced two polar lobes and an equatorial disc, moving outwards. Though Eta Carinae is quite away, approximately 7,500 light-years, it is possible to distinguish in the nebula, many structures with the size of about the diameter of our solar system. Knots, dust lanes and radial streaks appear quite clearly in many images.

At the http://staff.polito.it/amelia.sparavigna/Astronomical-astrofractool-web.htm, I am comparing the imaging of Homunculus Nebula, obtained by Hubble Space Telescope, and that from the Gemini South Telescope.
See also http://arxiv.org/abs/1005.4323, A comment on Eta Carinae's Homunculus Nebula imaging.