## 4 Discussion
### The Process and Characteristics of a Solar Eclipse  
Our study was based on the measurements from the GMR on the day of eclipse and several days before and after eclipse occurred. During a solar eclipse, the sun might be totally or partially shaded by the moon, which could affect the irradiance level from the sun. Therefore, we tried to use the radiometer to observe the process of a solar eclipse. To describe the solar eclipse, we accurately calculated the eclipse obscuration, and it was determined as a covered-to-total solar disc surface ratio [28,29]. The non-covered ratio is shown with a blue dash line in Figures 6 and 7 for 26 December 2019 and 21 June 2020, respectively.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Date**} & \multirow{2}{*}{**Eclipse Phase**} & \multicolumn{3}{c}{**Ad (K)**} & \multicolumn{3}{c}{**\(\beta\) (\({}^{\circ}\))**} \\ \cline{3-8}  & & **22.235 GHz** & **25.0 GHz** & **30.0 GHz** & **22.235 GHz** & **25.0 GHz** & **30.0 GHz** \\ \hline \multirow{2}{*}{26 December 2019} & BE & 89.4 & 136.4 & 157.7 & 4.6 & 3.9 & 3.3 \\  & ME & 79.2 & 121.1 & 142.3 & 4.7 & 3.8 & 3.4 \\ \hline \multirow{2}{*}{21 June 2020} & BE & 86.1 & 127.6 & 150.3 & 4.6 & 3.7 & 3.4 \\  & ME & 29.8 & 44.7 & 52.5 & 4.6 & 3.9 & 3.3 \\ \hline \end{tabular}
\end{table}
Table 4: The parameters obtained by curve fitting with the Gaussian function at each of the three frequencies. BE means “before eclipse” and ME means “maximum eclipse”.  
Figure 5: The variation of T\({}_{\rm B}\) increment during the scanning of the sun at the azimuth on 21 Jun 2020. BE means “before eclipse” and ME means “maximum eclipse”. The dots are observed data and the line is a fitting of the Gaussian function (Gau). (**a**) 22.235 GHz, (**b**) 25.0 GHz, (**c**) 30.0 GHz.  
We calculated and analyzed the T\({}_{\rm B}\) increment of the sun as it reached the GMR antenna. The relationship between the eclipse obscuration and the T\({}_{\rm B}\) increment are also shown in Figures 6 and 7, the signed line curve gives the experimentally observed values, and we tried to achieve the closest agreement between the observed and theoretical eclipse curves. In order to compare the change between the eclipse obscuration and the T\({}_{\rm B}\) increment, we also provided the non-eclipse observation data. According to our observations, a good agreement between the calculated non-covered ratio curve and the observed eclipse curves were found at every frequency. Normally, the T\({}_{\rm B}\) increment had no obvious fluctuation during non-eclipse conditions, but the solar eclipse started to affect the T\({}_{\rm B}\) increment when it initially occurred (first contact), and this effect disappeared at last contact. The observation results showed that the T\({}_{\rm B}\) increment was at a minimum when the shadow area was at a maximum.  
Figure 6: The variation of the T\({}_{\rm B}\) increment (left axis) during the solar eclipse on 26 December 2019 (red solid curve with \(\ddagger\) marks) as compared with that before and after the solar eclipse on 22 December and 27 December (black curve with other marks). All times were local times (CST). The blue dash line represents the percentage of the unshaded solar disk area (right axis). (**a**) 22.235 GHz; (**b**) 25.0 GHz; (**c**) 30.0 GHz.