Niu LIU

Biography

I am a tenure-track Assistant Professor and PhD advisor at the School of Astronomy and Space Science, Nanjing University. I received my BSc and PhD in Astronomy from Nanjing University in 2015 and 2020, respectively. From November 2017 to October 2018, I was a visiting PhD student at the Paris Observatory, supported by the China Scholarship Council. In September 2020, I joined Nanjing University as a postdoctoral researcher under the Yuxiu Young Scholars Program.

Frontier Seminar in Astronomy: Mondays at 15:00, Tea Room 216, Astronomy Building. The seminar focuses on recent advances in astrometry and related fields.

Office Hours: Mondays, 9:00–11:00, Office 317, Astronomy Building.

Teaching

Spherical Astronomy (Undergraduate course, Spring semester, offered annually)

This course provides a systematic introduction to celestial coordinate systems, time systems, apparent motions of celestial bodies, precession and nutation, Earth rotation, and the fundamental theories of astrometry. Emphasis is placed on the intrinsic connection between spatial geometric modeling and observational data, making the course an important theoretical foundation for high-precision space-time reference systems and astrometric methods.

Astronomical Reference Systems (Graduate course, Spring semester, offered biennially; most recent offering: 2026)

This course introduces the principles underlying the realization of celestial and terrestrial reference systems, including the implementation of the ICRF and ITRF, Earth orientation parameters, and their applications in space geodesy, satellite navigation, and deep-space exploration.

Research Interests

● High-precision Astronomical Reference Frames: My research focuses on the construction, realization, and long-term maintenance of celestial reference frames. By combining Gaia space astrometry with ground-based VLBI observations, I aim to improve the accuracy of celestial position measurements and the stability of reference frames. This work supports astrophysical applications of microarcsecond-level astrometric data, as well as the development of high-precision space-time reference systems and deep-space navigation.

● Multi-wavelength Astrometry: My research explores unified modeling methods and systematic-error corrections for astrometric measurements at different observing wavelengths. It investigates the frequency-dependent positions of reference sources and the effects of their physical structures, supporting the comparison, combination, and consistency assessment of high-precision celestial reference frames.

Publications

● Publications and Selected Research Outputs: My research spans high-precision astrometry, celestial reference frames, Gaia–VLBI frame comparisons, multi-wavelength position measurements, and pulsar-timing astrometry. The results have been published in international journals such as The Astrophysical Journal and Astronomy & Astrophysics. Selected publications include:

○ Liu N., Yang J., Cheng X., Zeng A.-L., Chen W., Yang X.-L., Hong X., Zhang X.-X., Liu J.-C., & Zhu Z., “Detections of Nearly Bias-free Core Shifts with 5–30 μas Precisions at 8–43 GHz in BL Lacertae,” The Astrophysical Journal, 1003, 54 (2026).

○ Liu N., Zhu Z., & Liu J.-C., “Secular aberration drift in stellar proper motions: An additional term due to the change in line-of-sight direction,” Astronomy & Astrophysics, 688, L24 (2024).

○ Liu N., Zhu Z., Antoniadis J., Liu J.-C., & Zhang H., “Systematics of planetary ephemeris reference frames inferred from pulsar timing astrometry,” Astronomy & Astrophysics, 674, A187 (2023).

○ Liu N., Lambert S. B., Charlot P., Zhu Z., Liu J.-C., Jiang N., Wan X.-S., & Ding C.-Y., “Comparison of multifrequency positions of extragalactic sources from ICRF3 and Gaia EDR3,” Astronomy & Astrophysics, 652, A87 (2021).

○ Liu N., Lambert S. B., Zhu Z., & Liu J.-C., “Systematics and accuracy of VLBI astrometry: A comparison with Gaia Data Release 2,” Astronomy & Astrophysics, 634, A28 (2020).

● Complete Publication List: For more publications, citation information, and updated records, please visit my NASA ADS publication library.