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<p><strong><span style="font-size:20px;">IAU Symposium 401: Advancing Reference Systems, Ephemeris, and Standards</span></strong></p>
<div><br>
<span style="font-size:16px;">Dear Colleagues,</span><br>
</div>
<div><span style="font-size:16px;">It is our pleasure to announce that the International Astronomical Union (IAU) Symposium</span></div>
<div><span style="font-size:16px;">"Advancing Reference Systems, Ephemeris, and Standards: from the Earth and the Moon</span></div>
<div><span style="font-size:16px;">to Solar System Bodies" (IAUS 401) will be held from August 4 to 9, 2025, at the National</span></div>
<div><span style="font-size:16px;">University of La Plata (UNLP), La Plata (Argentina).</span></div>
<div> </div>
<div><span style="font-size:16px;">Reference systems and their standardization are of paramount importance to many fields</span></div>
<div><span style="font-size:16px;">of astronomy. Some examples are the reduction of ground-based observations, space</span></div>
<div><span style="font-size:16px;">astrometry, astrophysics missions, and space missions to solar system planetary bodies</span></div>
<div><span style="font-size:16px;">and beyond. The concept of a reference system and its realization requires the</span></div>
<div><span style="font-size:16px;">convergence of reference frames, ephemeris, and time scales to be developed respecting</span></div>
<div><span style="font-size:16px;">associated standards, thus fulfilling one of the IAU strategic goals as the provider of</span></div>
<div><span style="font-size:16px;">astronomical standards and their use.</span></div>
<div><span style="font-size:16px;">The IAUS 401 will provide a forum to discuss the latest results and prospects in these</span></div>
<div><span style="font-size:16px;">fields and thus facilitate the coordination of common standards across agencies and</span></div>
<div><span style="font-size:16px;">organizations.</span></div>
<div><br>
<span style="font-size:16px;">The IAUS 401 is structured in six key topics:</span></div>
<div><br>
<span style="font-size:16px;"><em>1.- Earth rotation models and Earth Orientation Parameters (EOP)</em></span></div>
<div><em><span style="font-size:16px;">2.- Celestial and terrestrial reference systems/frames</span></em></div>
<div><em><span style="font-size:16px;">3.- Reference systems/frames for the Moon and other solar system bodies</span></em></div>
<div><em><span style="font-size:16px;">4.- Time scales and time metrology</span></em></div>
<div><em><span style="font-size:16px;">5.- Ephemerides of solar system objects</span></em></div>
<div><em><span style="font-size:16px;">6.- Astronomical standards</span></em></div>
<div><br>
<span style="font-size:16px;">The IAUS 401 registration, abstract submission, and IAU travel grant applications are</span></div>
<div><span style="font-size:16px;">already open. The symposium will be in a hybrid format to welcome in-person and online</span></div>
<div><span style="font-size:16px;">participation.</span></div>
<div><span style="font-size:16px;">For additional information and contact details, please refer to IAUS 401 website:</span></div>
<div><span style="color:#0000ff;"><u><span style="font-size:16px;">https://iaus401.fcaglp.unlp.edu.ar/</span></u></span></div>
<div><br>
<span style="font-size:16px;">We are looking forward to seeing you in La Plata!</span></div>
<div><span style="font-size:16px;">Sincerely,</span></div>
<div><br>
<span style="font-size:16px;">Alberto Escapa and Laura I. Fernández,</span></div>
<div><span style="font-size:16px;">On behalf of the SOC and the LOC</span></div>
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<div dir="ltr" style="color: rgb(32, 33, 36); font-family: Arial, Helvetica, sans-serif; font-size: small; background-color: rgb(255, 255, 255);"><font color="#000000"><font face="arial, sans-serif">Geof. Mercedes Gil </font><br>
<font face="arial, sans-serif">Secretaria de Posgrado </font></font></div>
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<div dir="ltr" style="color: rgb(32, 33, 36); font-family: Arial, Helvetica, sans-serif; font-size: small; background-color: rgb(255, 255, 255);"><font color="#000000" face="arial, sans-serif">Facultad de Ciencias Astronómicas y Geofísicas<br>
Universidad Nacional de La Plata</font>
<div><font color="#000000" face="arial, sans-serif"><b style="line-height: 16.5px; background-color: rgb(252, 252, 252);">Teléfono</b><span style="line-height: 16.5px; background-color: rgb(252, 252, 252);">: (0221) - 423 - 6593 int. 1050</span><br>
<a href="http://www.fcaglp.unlp.edu.ar/area-docente/posgrado/posgrado" style="margin: 0px; padding: 0px; outline: none; background-image: initial; background-position: initial; background-repeat: initial;" target="_blank">http://www.fcaglp.unlp.edu.ar/posgrados</a></font><br>
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