What is a Faculae?

Those of you who study astronomy or space science have probably heard of the sunspots and faculae. These are regions of light that shine from the sun. They are areas where the sun is shining in white light, or where the solar irradiance is high enough to be visible. There are some models of the formation of faculae, and we can use this knowledge to understand how they formed. We can also look at the sun in the sky in white light, and find that there are different variations in total irradiance.

Observations of the sun in white light

A white light solar filter is a great way to view the Sun’s photosphere. It removes most of the sunlight before it enters the eyepiece. This reduces the intensity of the light by up to 100,000 times.

The photosphere is the thin outer layer of the Sun. It is composed of gas and plasma that is less than one percent of the atmosphere of Earth. Light is emitted by excited hydrogen atoms. These atoms emit specific wavelengths, and the light from the photosphere is similar to light coming from a solid glowing body.

When looking at the Sun, you may see it as a red or orange color, or a yellow or white light. Depending on the seeing conditions, you might not be able to see much detail.

When observing the Sun, you should always use good eye protection. Never look directly at the Sun, as you might hurt your eyes. Instead, hold a piece of paper or thick cardboard behind your eyepiece.

With a white light solar filter, you’ll be able to see sunspots, prominences, and other features in the photosphere. You can also see the disk of the Moon during a solar eclipse.

Another option for observing the Sun is a pinhole camera. To build a pinhole camera, you’ll need a tiny hole in a piece of thick paper or cardboard. Once you’ve made the hole, you can project the image onto a second piece of paper. This technique will result in a small image of the Sun, but it will reveal the progress of a partial solar eclipse.

Finally, a H-alpha telescope is a great way to see the surface of the Sun. You’ll be able to find prominences, granules, and other features in the Sun’s photosphere.

Models of the formation of faculae

Faculae are relatively bright and hot regions of the photosphere of the Sun. They can be found on the limb or the disc, and they are characterized by a relatively strong magnetic field. There are many types of faculae. Some have been called flocculi, hollows, and pits.

The magnetic field of faculae is unipolar. However, observers suggest that the magnetic field of faculae is multipolar. This implies that they are a type of magnetic vortex. It is not entirely clear, however, what is responsible for the multipolar character of the field.

A number of mathematical models have been developed to explain the formation of faculae. One, the “hillock and cloud model”, describes enhanced brightness in regions near sunspots.

Another theory, the “tachocline dynamo”, explains the long-period oscillations in the faculae. These are caused by significant masses of gas.

Finally, models using the Ceres crater production function suggest that impact-induced lateral mixing is a possible process for burying the faculae. Since impacts may have triggered aqueous activity in the early history of Ceres, the salt deposits found there could be related to liquid brines that had frozen in the impact region.

Faculae are relatively dense, with a density about 15 times that of the surrounding photosphere. Because of the large number of particles, these structures are relatively high in temperature. In fact, they are 1000 K warmer than the average photosphere.

A number of researchers have devoted a lot of attention to the problem of the structure of these features. Most of the models have been developed within the context of mean field theory. Yet, these models do not explain the long-period oscillations, which are not attributed to MHD waves.

Variations in total solar irradiance caused by sunspots

The Sun is the main source of energy for the solar system. It provides energy to Earth in the form of radiation. In turn, the Sun has a large influence on the climate of our planet.

Sunspots are large, dark splotches that emerge from the Sun’s surface. They are formed when magnetic ropes travel through the interior of the Sun. As the ropes pass by, they form a sunspot. These spots have a strong magnetic field, which prevents convective heat flow to the surface.

When a sunspot disappears, the total solar irradiance (TSI) decreases. However, some experts argue that these decreases are not related to changes in solar activity.

One explanation is that the Sun’s magnetic field is weaker during Grand Solar Minimums. The reduced field will reduce the amount of heating emitted by the Sun, which in turn will lead to a reduction in terrestrial temperature.

Another explanation is that the sunspots are not the only feature of the Sun. Diffuse bright areas, called faculae, are also present on the solar disk. Faculae are more diffuse and easier to see near the edges of the disk.

The increase in the brightness of features like these exceeds the dimming of sunspots. This can explain how a short-term decrease in TSI results from a sunspot, but not the longer-term decrease.

During the most recent Grand Solar Minimum, the sunspot numbers have declined significantly. Nevertheless, other features of the 11-year solar cycle continue to occur.

A model of the sunspots and TSI variation suggests that the phase relation between the two is very well-defined. The authors find a correlation coefficient of 0.94 for the daily composite TSI between 1991 and 2021.

Age differences between faculae and Occator crater

The origin of Occator’s bright deposits has been debated. It is thought to be an accumulation of salts. But new work suggests that it is similar to the same process occurring on Ceres, the moon closest to the Sun.

A possible explanation for the distribution of bright material in the Occator crater is impact-induced fracturing. Initially, impact-generated fractures dug out the crater. Impact heating then mobilized deep-seated brine reservoirs, which were later exposed as vents. In turn, these vents allowed water and dissolved gases to erupt. These events led to the formation of a system of fractures and a network of bright, carbonate-rich material.

However, crater count measurements suggest that the maximum age for the crater is 18 Ma. Several asteroid-flux derived chronology models provide ages of 1 to 53 Ma, although statistical errors on these ages are usually on the order of a few millions of years.

However, the model ages are not peer-reviewed. The crater count may be a more accurate estimate of the age of Occator’s bright deposits. This is because the crater counts for small count areas (areas with less than 10 craters) are generally lower than those of larger areas. Consequently, small craters tend to be more susceptible to degradation and erasure.

Another explanation for the Occator’s bright material is that it was sourced from a melt chamber. The crater has a jagged ridge. The ridge is interpreted as a remnant of a former central mountain. Phyllosilicates cover the surface of the crater. As temperatures rose, gases forced carbonate-rich materials to ascend. They then erupted from the fractures, eventually forming a bright dome.

Conclusions

The sunspot-faculae relationship is one of the key factors in solar physics. Faculae are the bright areas of the photosphere that precede the formation of sunspots. Faculae have a significant influence on the total irradiance of the solar disk. They are approximately two times hotter than the ambient plasma, emitting an extra 15% energy.

A number of studies have looked at these processes. Although they may explain some of the excess irradiance during the solar maximum, there is still a large part of the excess that cannot be explained by faculae.

One way to look at this relationship is to compare the total irradiance to the area of the sunspot. This ratio is calculated by smoothing the irradiance during the 11 year sunspot cycle. It is found that the average value for the ratio is 16.7 +- 0.51.

Other types of features that have been studied are hollows and pits. Hollows are steep sided flat bottomed depressions. Pits are much larger, and occur in fields as large as tens of kilometers in diameter.

Another observable phenomenon is the long-period oscillations in faculae. These oscillations can last from a few minutes to a few hours. However, they are not always associated with MHD waves. Most researchers interpret these oscillations as the manifestation of acoustic waves.

Although the structure of the faculae is not yet understood, a new approach can be taken by looking at the structure of the sunspot. A proposed model describes periodic concentric rings and segmental brightening.

A more comprehensive analysis is required to reach a definitive conclusion on the connection between faculae and sunspots. In the meantime, this information can be used to develop a more accurate understanding of irradiance variations.

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