Talk:Gaia (spacecraft)

What about stars brighter than magnitude 5.7?

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: http://dx.doi.org/10.1051/0004-6361/201629272, 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

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)

Gaia italics?

I recently reverted an edit that italicized the name Gaia throughout the article. Upon removing the new italics, I saw that the article was inconsistent in its usage (for example, most of the occurences in the lead were italicized). I notice that the ESA web pages on Gaia do not italicize the name and, by analogy, the article on the satellite Hipparcos, a direct precursor of Gaia, does not italicize that spacecraft's name. The Manual of Style also notes that "most real-world spacecraft and rockets at this time are not given proper names, thus [italics] are not appropriate". In the interest of consistency, I recommend that we delete the remaining italics for Gaia in this article. --SteveMcCluskey (talk) 02:32, 11 December 2017 (UTC)

Gaia looks like a proper name to me. It is a single object and it is called Gaia. Same as Challenger, for example. --mfb (talk) 07:15, 11 December 2017 (UTC)

Yes, it is a proper name and named spacecraft on Wikipedia are italicized (not the projects, which cover the "most real-world spacecraft" in your post, but the individual craft if they have a specific name). As the reverted italicizer of the title, thanks for bringing this to the talk page. Randy Kryn (talk) 10:28, 11 December 2017 (UTC)

Thanks for the comment, here's the full paragraph from MOS:

The vessels convention does not apply to smaller conveyances such as cars, trucks, and buses, or to mission names. Also, most real-world spacecraft and rockets at this time are not given proper names, thus Apollo 11, Saturn V, Falcon 9, etc. are not appropriate.

A further check of the actual usage in Wikipedia makes Hipparcos an outlier; Spirit (rover); Magellan (spacecraft); Voyager 2 and Cassini-Huygens are all italicized, although Apollo 13 is not. It llks like your plan to italicize Gaia may be appropriate, although it doesn't quite follow MOS. Perhaps some clarification at MOS is in order. --SteveMcCluskey (talk) 14:54, 11 December 2017 (UTC)

I've read more about it as well, and from our description it seems like a named capsule, probably on the order of Friendship 7 and the other named capsules of the Mercury program. I'm glad you objected, thank you, it's given me a chance to learn more about this spacecraft and what it's accomplishing. Randy Kryn (talk) 17:00, 11 December 2017 (UTC)

It is not a "smaller conveyance[] such as cars, trucks, and buses" and most of the time it is not used as mission name. While most spacecraft don't have real names, Gaia does. Apollo 13 is a systematic name - the 13th (sort of) mission of the Apollo program. --mfb (talk) 21:05, 11 December 2017 (UTC)

@Mfb: Thanks for the comment. You might want to contribute to the discussion at Wikipedia_talk:Manual_of_Style/Text_formatting#Spacecraft_names_(once_more).--SteveMcCluskey (talk) 21:40, 11 December 2017 (UTC)

@Randy Kryn:After discussion at Wikipedia_talk:Manual_of_Style/Text_formatting#Spacecraft_names_(once_more) the Manual of Style was clarified to indicate that a spacecraft's name should be italicized but a mission name should not be "except where it coincides with a craft's name".

Therefore, Gaia should consistently be in italics. Since you've made additional edits since my deletion, could you please restore those I've removed. Thanks. --SteveMcCluskey (talk) 02:33, 20 December 2017 (UTC)

Thanks. And the article is an interesting read either way. Randy Kryn (talk) 10:12, 20 December 2017 (UTC)

Interferometry??

How does the name “Gaia” imply the use of interferometry? I am inclined to strike that line unless someone can explain this to me. It makes no sense and can be confusing or the reader.

“Despite its name, Gaia does not actually use interferometry to determine the positions of stars” OriEri (talk) 00:06, 17 January 2019 (UTC)

Read the History section. It states: "The name "Gaia" was originally derived as an acronym for Global Astrometric Interferometer for Astrophysics. This reflected the optical technique of interferometry that was originally planned for use on the spacecraft. While the working method evolved during studies and the acronym is no longer applicable, the name Gaia remained to provide continuity with the project.[21]" Cheers, Rowan Forest (talk) 01:00, 17 January 2019 (UTC)

While true I agree with OriEri the line in Measurement Principles is unnecessarily confusing because of the lack of context. It's already been explained in the History section in a more complete and less confusing way, so it seems superfluous here. All that section needs to say it was originally an interferometer and now it's not.ChiZeroOne (talk) 01:13, 17 January 2019 (UTC)

Gaia will create a precise three-dimensional map ...

This implies that it hasn't yet started doing so. — Preceding unsigned comment added by 31.50.84.235 (talk) 11:41, 5 February 2019 (UTC)

Launched in 2013, anyone can figure it is in the process of mapping. Rowan Forest (talk) 23:32, 5 February 2019 (UTC)

Inconsistencies in claims towards exoplanet detection

The article (as well as ESA's statements) are inconsistent with regards to exoplanet detection. While the introduction as well as ESA's original description of Gaia do mention planetary detection, Gaia's current mission status clearly states that Gaia's radial velocity measurement equipment will not be sensitive enough to detect exoplanets.. The article should thus be changed accordingly or at least include this more recent assessment of Gaia's capabilities (Pcauchy (talk) 13:34, 15 March 2019 (UTC))

The detections are expected to come from astrometry (detecting periodic variation of the position of the star in the sky), not from radial velocity measurements. --mfb (talk) 14:03, 15 March 2019 (UTC)

References

Early Data Release 3 Images

@Drbogdan: An IP recently changed two images to reflect the latest data release (EDR3). These images were reverted by Drbogdan because the older image "seems better" and requested comment on talk.

I have restored the IP's edit since it reflects the current status of Gaia data releases; I trust this is satisfactory. --SteveMcCluskey (talk) 21:59, 12 December 2020 (UTC)

@SteveMcCluskey: Thank you for your comments - yes - all seems ok after all - no problem whatsoever - Thanks again - Stay Safe and Healthy !! - Drbogdan (talk) 22:49, 12 December 2020 (UTC)

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No data on Bete

From the Betelgeuse article:

Although the European Space Agency's current Gaia mission was not expected to produce good results for stars brighter than the approximately V=6 saturation limit of the mission's instruments, actual operation has shown good performance on objects to about magnitude +3. Forced observations of brighter stars mean that final results should be available for all bright stars and a parallax for Betelgeuse will be published an order of magnitude more accurate than currently available. There is no data on Betelgeuse in Gaia Data Release 2.

There should be similar information on difficulties with bright stars in the Gaia article. -- Dan Griscom (talk) 12:47, 17 September 2023 (UTC)

Some references:

- "Gaia observations of naked-eye stars: status update" (2016): https://iaus330.sciencesconf.org/data/pages/vbs_A0.pdf

- "Gaia Early Data Release 3 - Q&A - Bright Stars" (December 3, 2020): https://www.youtube.com/watch?v=1TsggnXA2Zg

- "Gaia Early Data Release 3" (April 28, 2021): https://www.aanda.org/articles/aa/full_html/2021/05/aa39498-20/aa39498-20.html#S8 Dan Griscom (talk) 13:07, 17 September 2023 (UTC)

Why does it need precise pointing when it is constantly spinning ?

Under Mission progress it says "The limiting factor to further mission extensions is the supply of nitrogen for the cold gas thrusters of the micro-propulsion system. The amount of dinitrogen tetroxide (NTO) and monomethylhydrazine (MMH) for the chemical propulsion subsystem on board might be enough to stabilize the spacecraft at L2 for several decades. Without the cold gas, though, the space craft can no longer be pointed on a microarcsecond scale." - but Gaia is constantly spinning (6 hr rotation period) so the only thing that is pointed is the axis of rotation ? What is the impact on data collection when cold gas runs out ? - Rod57 (talk) 12:20, 11 December 2024 (UTC)