MALOLOS CITY—If you missed Monday night’s lunar halo, do not despair, because there are more optical phenomena that can be seen every night 6,000 meters above us in the coming days.
Frederick Gabriana, a professor at the Rizal Technological University (RTU) said as the weather gets colder, lunar halos can be seen in the nights to come. “We can expect more moon bows in the days ahead,” said Gabriana noting that the optical phenomenon usually occurs during cold weather which leads to the formation
of ice crystals in the atmosphere.
As a mathematician, Gabriana said that ice crystals formed in the earth’s atmosphere are just 6,000 meters above the surface of the earth. He said that average coldest day of the year in Metro Manila is January 26.
This means that there is more possibility of seeing lunar halos in the sky in the two weeks. However, the mathematician said that the appearance of the optical phenomenon is dependent on the cloud formation.
“It depends on the presence of cirrostratus clouds,” he said and explained that specific type of cloud that produces halos are called cirrostratus nebulosus. Gabriana said that nebulosus species is featureless and uniform and is formed by gently rising air.
“If the sun or moon shines through this kind of cloud, a halo is formed,”he said. He added, “cirrus clouds are made up of ice crystals that are usually hexagonal in shape. These kind of crystals usually refract light by 22 degrees. Thus it forms a halo 44 degrees in diameter. Because of the different wavelengths, the inner side of the halo is usually reddish while the outer side is usually bluish.
The red halo is 21.54 degrees in radius and the blue halo is 22.37 degrees in radius. That’s why it looks somewhat like a rainbow around the moon.” On Monday night, skywatchers here were amazed at the ring formation around the moon.
Some called it moon bow, but astronomers said its proper name is “lunar” or moon halo, The appearance of the lunar halo was repeated on Tuesday night. However, the appearance on Monday was brighter. As this developed, Gabriana said that changing brightness of the moon is caused by its phase.
It meant that the moon is brightest when it is opposite the sun. So the halos are brighter during full moon. He also said that ice crystals are formed because it is cold in the northern hemisphere. “Remember that it
is warm in the southern hemisphere now. So the distance between the earth and sun is not the reason for the seasons.
It’s the tilt of the earth’s axis that causes it. In fact, the earth just passed perihelion so it is actually closer to the sun now.,” he said.
