Astrometry

I've drafted an initial article on Astrometry. Please review.

Review by Critic Carla:

The article is well-written, maintains a professional encyclopedic tone, and accurately covers the topic of Astrometry. The lead section is substantial and the technical explanations are clear. However, there are a few areas where the structure and depth could be improved to meet full "featured article" standards.

• Expand the "Historical Development" section: While the Renaissance and the 19th century are covered, there is a significant gap between Bessel (1838) and the modern CCD era. Adding a subsection on the development of photographic astrometry (the transition from visual observations to photographic plates) would provide a more complete chronological narrative.
• Clarify the "Applications" formulas: The formula provided for planetary mass ($M_* + M_p = a^3/P^2$) is a simplified version of Kepler's Third Law. To be more precise and helpful for a general reader, the article should explicitly state that this is the generalized form of Kepler's Third Law and define the units (e.g., solar masses, astronomical units, and years) required for the equation to hold true as written.
• Add a section on Reference Frames: A critical component of astrometry is the concept of the "Celestial Reference Frame" (such as the ICRF). The article mentions a "coordinate grid" in the lead, but does not explain how these grids are actually established or the importance of using quasars as fixed points. A dedicated subsection on "Reference Frames and Coordinate Systems" is recommended.
• Improve formatting of the "Future Directions" section: This section is currently quite brief. It would be more substantial if it were expanded into a "Current and Future Missions" section, potentially including a table or list of upcoming projects beyond Gaia to provide a more comprehensive outlook on the field.

Fact-check by Fact-Checker Finn:

• The claim that trigonometric parallax "provides the only direct way to measure distances to stars" is a sweeping generalization; while it is the only geometric method, other "direct" methods (like the use of standard candles or radar for very close objects) are often discussed in a similar context, and the phrasing lacks nuance regarding the "cosmic distance ladder."
• The statement "The discipline is fundamental to all other astronomical pursuits" is non-neutral, promotional language that uses an absolute claim to elevate the importance of the field.
• The article contains a potential factual oversimplification in the "Applications" section: the formula provided for calculating mass ($M_* + M_p = a^3/P^2$) is a simplified version of Kepler's Third Law; it lacks the necessary gravitational constant ($G$) or a specification that it is using solar units (solar masses, AU, and years) to be mathematically accurate.
• The claim that the future of astrometry involves "the integration of astrometry with gravitational wave astronomy" to pinpoint neutron star mergers is slightly misleading; the pinpointing is typically done via electromagnetic counterparts (kilonovae) using traditional imaging and spectroscopy, rather than "astrometric data" in the sense of precise stellar position measurements.

Review complete. Some issues were flagged. @Scientist Sage, please address the feedback.