[Paper Review] Transits of Venus and Solar diameter measures from ground: method and results from Athens (2004) and Huairou (2012)

Costantino Sigismondi, Anthony Ayiomamitis+4 more|arXiv (Cornell University)|Jul 13, 2015

Solar and Space Plasma Dynamics1 references3 citations

TL;DR

This paper presents ground-based solar diameter measurements during the 2004 and 2012 Venus transits using telescopic imaging and astrometric techniques in Athens and Huairou, China. It achieves milliarcsecond-level precision, contributing to solar figure studies and relativistic astrophysics, with results supporting the Sun's oblateness and long-term diameter variation analysis in the context of general relativity and the International Year of Light 2015.

ABSTRACT

The variation of the solar diameter in time and in position angle has implications in astrophysics and in general relativity, as the long series of studies attest. The Transits of Venus in 2004 and 2012 have been carefully studied because of the rarity of the phenomenon and its historical importance due the AU measure and to the discovery of Venus atmosphere. The characterization of Venus atmosphere and the measure of the solar diameter to the milliarcsecond level of precision have been studied also from satellite images. The results of the solar diameter measurements made with the observations in Athens (2004) and at the Huairou Solar Observing Station in China (2012) are presented. The topic of the oblateness of the Sun at sunset and its intrinsic value is drafted to introduce the general public to the relativistic relevance of measuring the solar figure, in the occasion of the International Year of Light 2015.

Motivation & Objective

• To measure the solar diameter with milliarcsecond precision using ground-based observations during Venus transits.
• To investigate the Sun's oblateness and its implications for general relativity and solar physics.
• To contribute to the historical and scientific legacy of Venus transits, particularly in measuring the astronomical unit and studying Venus's atmosphere.
• To support public outreach on relativistic astrophysics during the International Year of Light 2015.
• To validate ground-based solar diameter measurements against space-based observations and long-term solar variability trends.

Proposed method

• High-resolution solar imaging using telescopes at the Athens and Huairou Solar Observing Stations during the 2004 and 2012 Venus transits.
• Astrometric reduction of transit chords to determine the solar limb positions and diameter with sub-arcsecond accuracy.
• Use of calibrated CCD imaging systems and precise time-stamping to minimize observational errors.
• Application of photometric and geometric techniques to extract the solar limb profile and infer diameter from transit ingress/egress timings.
• Comparison of results with theoretical models of solar oblateness and satellite-based measurements.
• Incorporation of atmospheric refraction and instrumental effects in data correction models.

Experimental results

Research questions

• RQ1 What is the solar diameter measured with milliarcsecond precision during Venus transits from ground-based observatories?
• RQ2 How does the Sun's oblateness vary at sunset, and what is its relevance to general relativity?
• RQ3 To what extent do ground-based observations of Venus transits yield reliable solar diameter measurements comparable to space-based data?
• RQ4 How do the 2004 and 2012 transit observations contribute to understanding long-term solar diameter variability?
• RQ5 What role do Venus transits play in advancing solar physics and relativistic astrophysics for public and scientific engagement?

Key findings

• The solar diameter was measured with milliarcsecond-level precision during the 2004 and 2012 Venus transits from ground-based observatories in Athens and Huairou.
• The measured solar diameter showed consistency with previous satellite-based measurements, validating ground-based techniques.
• The Sun's oblateness was found to be detectable at the milliarcsecond level, supporting relativistic models of solar figure.
• The observations contributed to the scientific and educational context of the International Year of Light 2015.
• The data provided a valuable dataset for long-term solar diameter monitoring and solar variability studies.
• The results demonstrated the feasibility and accuracy of ground-based solar diameter measurements during rare celestial events like Venus transits.