As part of the tests to try and diagnose the stray light issue noticed in the first month of instrument commissioning, the Gaia operations team is making a series of spacecraft orientation changes.
The spacecraft was first tilted from 45 to 42 degrees and then to 0 degrees, that is, facing its sunshield directly at the Sun. Then the spacecraft was returned to 45 degrees.
Gaia tilt seen from Earth
Astronomers Peter Veres and Bryce Bolin, who were following a call for Earth-bound observations to improve the prediction of Gaia’s brightness under different viewing conditions, used the 2.24m telescope on Mauna Kea in Hawaii to capture Gaia’s tilt from 0 to 45 degrees on 27 February.
The resulting movie nicely illustrates the change in brightness of the spacecraft over a period of around half an hour (12:14:52 UT to 12:42:06 UT), as Gaia’s sunshield tilted away from the Earth. Gaia is the bright object in the centre of the movie and moves downwards.
Dave Tholen, who processed the images, said: “We started with 10 second exposures for the first 30 exposures, then increased the exposure time to 20 seconds to get images 31 to 35, then increased again to 40 seconds for images 36 to 40. The last three exposures were 80 seconds each.”
The observations also captured a main belt asteroid (2002 RS34) moving from top centre to the right of the field of view in the movie.
As for the issue of stray light, the data are still being analysed. The tilting process will be repeated again, at a much slower rate, in order to gather more information from on-board systems during the transition period.
This is a Hubble Space Telescope composite image of a supernova explosion designated SN 2014J in the galaxy M82, at a distance of approximately 11.5 million light-years from Earth. Astronomers using a ground-based telescope discovered the explosion on January 21, 2014. This Hubble photograph was taken on January 31, as the supernova approached its peak brightness.
São Paulo poised to join megatelescope
Nature 506, 7489 (2014). http://www.nature.com/doifinder/10.1038/506417a
Author: Elizabeth Gibney
Brazilian state mulls support for Giant Magellan Telescope.
Einstein’s lost theory uncovered
Nature 506, 7489 (2014). http://www.nature.com/doifinder/10.1038/506418a
Author: Davide Castelvecchi
Physicist explored the idea of a steady-state Universe in 1931.
The remnant of a merger between two dwarf galaxies in Andromeda II
Nature 507, 7492 (2014). doi:10.1038/nature12995
Authors: N. C. Amorisco, N. W. Evans & G. van de Ven
Driven by gravity, massive structures like galaxies and clusters of galaxies are believed to grow continuously through hierarchical merging and accretion of smaller systems. Observational evidence of accretion events is provided by the coherent stellar streams crossing the outer haloes of massive galaxies, such as the Milky Way or Andromeda. At similar mass scales, around 1011 solar masses in stars, further evidence of merging activity is also ample. Mergers of lower-mass galaxies are expected within the hierarchical process of galaxy formation, but have hitherto not been seen for galaxies with less than about 109 solar masses in stars. Here we report the kinematic detection of a stellar stream in one of the satellite galaxies of Andromeda, the dwarf spheroidal Andromeda II, which has a mass of only 107 solar masses in stars. The properties of the stream show that we are observing the remnant of a merger between two dwarf galaxies. This had a drastic influence on the dynamics of the remnant, which is now rotating around its projected major axis. The stellar stream in Andromeda II illustrates the scale-free character of the formation of galaxies, down to the lowest galactic mass scales.