Talk:Gaia (spacecraft)

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What about stars brighter than magnitude 5.7?[edit]

Will they just not be measured?

The problem is that the CCDs will over-saturate observing brighter stars and therefore they are not capable of making accurate measurements. I know this from my own experience working on Gaia but there should be some paper/techdoc out there describing this... *search* -- Aepsil0n (talk) 14:46, 8 November 2012 (UTC)
I recently saw a discussion (on the Gaia website?) that they have made a software fix for handling star fields that include bright stars so that they'll be able to extract positions for even the brightest stars. I'll try to trace it down.--SteveMcCluskey (talk) 13:08, 21 September 2016 (UTC)
I've done some further digging and, checking the sources cited, have not been able to identify the source for the 5.7 magnitude limit. It is clear that ESA is in the process of developing methods for measuring very bright stars, using the point spread functions in the region surrounding the saturation area. A quotation from a forthcoming article in Astronomy and Astrophysics, T. Prusti and the Gaia Collaboration, "The Gaia mission", DOI:, describes the nature and current status of this process:
"The onboard detection is effective at the bright end down to magnitude G ∼ 3 mag: the detection efficiency is ∼94% at G = 3 mag and drops rapidly for brighter stars to below 10% for G = 2 mag. The 230 brightest stars in the sky (G < 3 mag, loosely referred to as very bright stars) receive a special treatment to ensure complete sky coverage at the bright end (Martín-Fleitas et al. 2014; Sahlmann et al. 2016). Using the Gaia observing schedule tool (GOST), their transit times and across-scan transit positions are predicted, based on propagated Hipparcos astrometry and the operational scanning law, and SIF [service-interface-function] data are acquired for these stars in the sky mapper (SM) and subsequently downloaded.… The reduction and analysis of these data are special, off-line activities, which are not yet operational. The ultimate scientific quality of these data will primarily depend on the achievable quality of the calibration of the sky-mapper detectors and point spread functions.… Because centroiding of these images in the uncalibrated detector frame can be carried out to within 50 µas, it is expected that a single-measurement precision of 100 µas will ultimately be achievable, which corresponds to end-of-life astrometry with standard errors of a few dozen µas."
We apparently need to state something like "ultimately Gaia will measure the positions of even the brightest stars", with appropriate citations to this article. --SteveMcCluskey (talk) 01:07, 22 September 2016 (UTC)
Done --SteveMcCluskey (talk) 01:40, 22 September 2016 (UTC)

Data releases[edit]

The third and subsequent dates for data releases are listed in the source as "TBC" (to be confirmed, no year specified). In particular, if the mission is extended by as much as four more years (and, dare we hope, more?), there could be even more releases beyond 2022. TomS TDotO (talk) 05:18, 21 September 2016 (UTC)

Agree that there seems to be some ambiguity about the later data releases; on the one hand the research community will want prompt access to the data as it is produced; on the other there will be later releases if the missin is extended. I suspect (no evidence as yet) that ESA will provide regular interim releases with the final release after end of mission. Any way we could express the ambiguity in the article without straying into WP:OR? --SteveMcCluskey (talk) 13:01, 21 September 2016 (UTC)

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