Abstract

A total solar eclipse is a spectacular celestial phenomenon, allowing a direct observation of the Sun’s chromosphere, prominences, and corona without the need of a solar filter during the totality. In contrast, an annular solar eclipse, also known as the “ring of fire”, presents a different viewing experience. Throughout the entire process of an annular eclipse, eye protection via a solar filter remains essential and it prevents us from observing the faint chromosphere and prominences. However, with good site selection and a well-designed observing plan, it is possible to capture the chromosphere and prominences during an annular solar eclipse. In this article, I share a successful observation of the chromosphere and prominences acquired during the annular solar eclipse that occurred on October 14, 2023.

1. Introduction

On October 14, 2023, an annular solar eclipse could be seen in the US, as well as Central and South America. I went to New Mexico to observe this eclipse and I planned to perform an interesting solar eclipse observation. In the past, there were very few reports of observations of the chromosphere and prominences during an annular solar eclipse1^,2^,3^,4^,5^,6. This is because the photosphere of the Sun is much brighter than the chromosphere and solar prominences. Those features are usually observed during a total solar eclipse when the Moon blocks the Sun’s disk completely and no solar filter is required. On the other hand, there is a small part of the Sun blocked by the Moon briefly during the second and third contacts in an annular solar eclipse. In particular, if one observes near the northern or southern limit of the eclipse path, the annular eclipse will feature an asymmetric ring, creating a prolonged edge effect due to the Moon's tangential movement. This opens a window for a longer display of Baily’s beads and for observing the chromosphere and prominences.

While Albuquerque is right at the center line (see Figure 1) with an annularity duration of nearly 5 minutes, in order to observe features such as Bailey’s beads, as well as the chromosphere and prominences that are usually seen during a total solar eclipse (Figure 2), I observed in Santa Fe, located near (< 20 km) the northern limit of the eclipse path (Figure 1). In Santa Fe, the annularity lasted for about 2.5 minutes with an asymmetric ring. In this article, I share my experience of imaging the Sun’s chromosphere and prominences during an annular solar eclipse.

2. Instrumental setup and observation

In this observation, I used an Astrophysics Traveler telescope (Diameter=105mm, focal length=610mm) with a 2x Barlow lens as the optical setup. The telescope was protected by a Thousand Oaks Type 3+ solar filter. For the sensor, I used a Canon 60Da camera controlled with SETnC running on a PC7. The setup of the instrument is shown in Figure 3. It is very important to make sure that the solar filter is on all the time except for imaging the chromosphere and prominences during the annular eclipse (see below).

The imaging sequence of the entire eclipse was triggered by a customized SETnC script. I started the imaging sequence just before the first contact and I took images every 5 minutes. At about 30 seconds before the 2nd contact (C2), the solar filter was removed. No visual observation through the camera is allowed from this point forward. High-frequency imaging with an exposure time of 1/4000s was performed until 10 seconds after C2. The solar filter was then put on to protect the camera and to image the asymmetric ring. The filter was removed again about 30 seconds before the 3rd contact (C3). High frequency imaging was performed to image the chromosphere and Baily’s beads. The solar filter was put on ~30 seconds after C3 and the remaining imaging sequence of the partial phase continued until the end of the eclipse.

3. Results

In Figure 4, I show the snapshots of the entire sequence of the annular solar eclipse. At about 30 seconds before C2, I removed the solar filter to image the prominences and chromosphere, and the results are shown in Figure 5. The images clearly show the prominences and chromosphere of the Sun from 30 seconds before the 2nd contact (C2) to 30 seconds after the 3rd contact (C3) when the solar filter was taken off.

4. Discussion

By observing near the northern limit of an annular solar eclipse path, I successfully imaged the prominences and chromosphere of the Sun without a solar filter. I also observed a longer duration of Baily’s beads. My observing site is about 17 km from the eclipse grazing zone where a broken annular eclipse can be seen. Inside the grazing zone, the sunlight goes through the lunar limb where the mountains and valleys on the Moon create a ragged edge producing a “broken ring”. Prolonged (can be more than a minute) Baily’s beads can be seen instead of a complete “ring of fire”. Future observations inside a grazing zone will be planned.

Acknowledgment

This project is partly supported by the National Science and Technology Council of the Republic of China (Taiwan) through grant 112-2112-M-007-042.