If you love sky gazing, the next couple of weeks are going to be busy for you. Three astronomical events are clustered near the coming weekend: the Geminids meteor shower, the last eclipse of 2020, and the lunar occultation of Venus. While the Geminids will be visible from most parts of the globe, the eclipse and the occultation can only be seen from a small fraction of the planet. In this article, let’s talk about the first event in line: the lunar occultation of Venus on December 13, 2020.
For more information on watching the Geminid meteor shower, see the video below. It is often regarded as the king of meteor showers! Don’t miss it.
What Is An Occultation?
An occultation is an astronomical event that occurs when one object is hidden by another object that passes between it and the observer. In other words, when the object in the foreground blocks the view of the object in the background, it is called an occultation.
But how is it different from the transit and an eclipse? Well, a transit occurs when the object in the foreground does not completely hide the object in the background. For example, when Mercury or Venus pass in front of the Sun as observed from the Earth, the event is known as a transit.
An eclipse is an astronomical event when a celestial body totally or partially disappears from the observer’s view either by an occultation or a transit. In simple words, if a shadow is cast onto an observer during an occultation or transit, it is called an eclipse.
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The term occultation is mostly used when the Moon passes in front of an astronomical object. The Moon’s orbit is inclined slightly to the ecliptic, meaning any stars with an ecliptic latitude of less than about ± 6.5 degrees may be occulted by it. Since the planets also lie in the ecliptic, they are often occulted by the Moon.
Lunar Occultation of Venus In December 2020
On December 13, The Moon will pass in front of Venus, creating a lunar occultation visible from parts of North America as shown below:
The map above shows the visibility of occultation across the world. Separate contours show where Venus’s disappearance is visible (shown in red) and where its reappearance is visible (shown in blue). Solid contours show where each event is likely to be visible through binoculars at a reasonable altitude in the sky. Dotted contours indicate where each event occurs above the horizon but may not be visible due to the sky being too bright or the Moon being very close to the horizon.
Outside of the contours, the Moon does not pass in front of Venus at any time, or is below the horizon at the time of the occultation. Lunar occultations are only ever visible from a small fraction of the Earth’s surface. Since the Moon is much closer to the Earth than other celestial objects, its exact position in the sky differs depending on your exact location on Earth due to its large parallax. The position of the Moon as seen from two points on opposite sides of the Earth varies by up to two degrees, or four times the diameter of the full moon.
This means that if the Moon is aligned to pass in front of a particular object for an observer on one side of the Earth, it will appear up to two degrees away from that object on the other side of the Earth.
For the rest of the world, the Moon will appear to pass very close to the morning star in the constellation of Libra.
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A Rare Alignment of Planets In December 2020
Though the lunar occultation of Venus is a rare astronomical event taking place in December 2020, the flagship event of the month (should say the year) is the great conjunction will take place on the day of the winter solstice. Interestingly, we had a major astronomical event on the Summer Solstice day, too: An annular solar eclipse.
Astronomers use the word conjunction to refer to a close approach of two celestial objects seen from the Earth. The term great conjunction is used for Jupiter and Saturn. On December 21, the solar system’s two gas giants will be one-tenth of a degree apart. In other words, the Earth, Jupiter, and Saturn will almost align.
The great conjunction takes place every 19.6 years on average. But the gap between the planets in the night sky varies. On 21 December 2020, the beasts will be closest to each other in nearly 800 years. Find all the details of this event in this article.