How do we understand Mercury crossing in front of the sun? How do we monitor it?

Hani Al - Dhalia

As Mercury nears the sun's disk, images of astronomical phenomena in our Arab countries and most of the world will spread on Monday 11 November 2019; some people think that Mercury is a hole or hole in the sun in the form of a deep black well that penetrates the surface of the sun .

But the fact is that it is a natural astronomical phenomenon to cross Mercury, which orbits Venus in two internal orbits between the Earth and the Sun, allowing them on certain occasions called "internal conjugation" to cross in front of the sun disk, they appear in the form of two dark spots compared to the bright glow of the sun Around them.

Mercury's current transit will last from one hour in the Eastern Arab countries to five and a half hours in South America, the peak of the event.

What transit?
It can be said that the transit phenomenon is very similar to the solar eclipse when the moon crosses in front of its disk; The eclipse is originally a transit, but is specific to the moon, while the term transit concerned the passage of planets Mercury and Venus in front of the sun disk, or even the passage of a celestial body or spacecraft.

Mercury crosses 13 times every 100 years, the last of which is in 2016, and the next time will be in 2032, 13 years later, while the flower occurs twice every 121.5 years, the last in 2012, and the next in 2117.

Mercury spot and sun disk
The virtual sun disk of the sky occupies about half of the 360-degree diameter of the full planetarium circle, or the equivalent of 1937 arc seconds on the day of transit, and the arc second is part of 3600 parts of the degree, the arc minute adjusts sixty arc seconds, and is called arc because Part of the 360 ​​° circle bracket.

On the day of the transit, because of the different position of the Earth from the Sun on the one hand and its position relative to the planet Mercury on the other hand (because of the orbits of Earth and Mercury, the ovals, when they approach the Sun and away from it at other times), the diameter of the planet Mercury will be ten arc seconds, that is, one sixth Arch micro.

This diameter is about 1/194 the diameter of the apparent solar disk that day, a tiny diameter that cannot be seen with the naked eye looking at the sun from behind the filters. For comparison, the diameter of the Sun is actually 109 times larger than Earth, 115 times larger than Venus, and 285 times Mercury.

How do we monitor transit?
It is well known that looking at the sun disk is not possible with the naked eye at any time of the day, except for some moments of sunset only, it is a great danger and certain damage to the eye, and therefore found safe means can be used to protect against the damage caused by the intensity of illumination The sun falling on the eye.

Looking at the naked eye on this particular occasion will be of little use until sunset when its rays completely subside. The naked eye cannot distinguish Mercury in front of the sun to finish its smallness. The only way is to use magnifying lenses such as a telescope or Telescope. Using these tools here is one of two ways:

Method 1: Directly look at the sun through the telescope / trail after placing a filter in front of the object, until pure and clear sunlight enters without heat and a strong beam.

The second method is the projection of the image of the sun through the telescope / drbel on a piece of white cardboard, where the sun disk will appear clearly, and the planet Mercury will appear a circular spot, and will appear sunspots if any and any object crossing in front of the sun at that moment as an aircraft or so.

Doha students monitor the crossing
Transit starts in Doha about one hour and 11 minutes before Mercury begins entering from the upper left edge of the sun disk at 15:35 pm, and continues until sunset at 16:46 pm.

From the green hill in the southwest corner of the cultural district (Katara) in Doha, about 500 students from various state and international schools and community schools will gather on the afternoon of the event as part of the so-called Qatar National Olympiad Astronomy Contest. In addition to the rare annular solar eclipse project in Qatar and a number of Arab countries in late December.

Supervising astronomers will provide a number of telescopes to allow students, their parents and those interested in watching the crossing in scientific and safe ways.