Visual and H-alpha measurements of solar diameter of 9 may 2016 mercury transit

TL;DR

This study compares visual and H-alpha measurements of the 2016 Mercury transit to evaluate solar diameter variations and active regions, finding a slight radius variation and questioning the Sun's oblateness at minimum activity.

Contribution

It provides a comparative analysis of solar diameter measurements in visible and H-alpha light during Mercury transit, challenging the oblate Sun theory at minimum activity.

Findings

Detected a -0.12" variation in photospheric radius

Identified 1.84" of active H-alpha regions at transit latitude

No confirmation of Sun's oblateness at minimum activity

Abstract

Visual observations of 2016 Mercury transit ingress made in visible light (Rome) and in H-alpha line (Tehran) are compared to evaluate the quote 1.84" of active H-alpha regions at the solar latitude of the transit, without a confirmation of the theory of an oblate Sun at minimum activity. A variation of -0.12" in the photospheric radius, within 0.17" is found.