Planetary Conjunction – What is it?

When astronomical objects such as moons, planets, stars, and asteroids appear to be close together in the sky to some degree as observed on Earth, an occurrence happens that’s called planetary conjunction. In astronomy, a number of coordinate systems are utilized to determine where an object appears in the sky, similarly with Earth’s longitude and latitude system.

The celestial coordinate system ascension and declination are fixed to certain standard points in the sky and aligned with the Earth’s tilt. Another is the ecliptic coordinate system that is fixed to the orientation of our Solar System within our galaxy. It is measured in ecliptic longitude and latitude. They are considered to be in conjunction with one another if two objects have the same ecliptic longitude or have the same right ascension.

As for our Solar System, the planets orbit the Sun in an elliptical fashion, slightly inclined with regard to one another. Also, other planets seem to roam about in the sky from our point of view on Earth. Planets received credits as “wandering stars” by early astronomers for the way they moved in the night sky, which was far more quickly than “fixed” stars. These planetary bodies in our Solar System often appear as pinpricks of light when seen at night, and they seem to occupy the same space in the night sky because of their alignment. In fact, they are millions of miles away from one another.

A phenomenon of perspective, conjunction is an event seen by an observer on Earth involving two astronomical bodies. Conjunctions involving the Moon have the greatest difference when it comes to times and details on account of its relative closeness on Earth. Still, it doesn’t differ by more than a few hours. One can see conjunctions between the Moon and bright stars or even between planets themselves, so a wide range of combinations is possible. At times, the conjunction involves more than two objects, such as two planets in conjunction and joined by the Moon.

In special cases, Mercury or Venus transit across the face of the Sun, and there are times when fascinatingly close conjunctions set two objects in the same field of view of a telescope by some degree. There are two types of conjunctions. One is the superior conjunction which happens when the planet’s inner or outer orientation lies on the other side of the Sun to Earth. Another is the inferior conjunction, which is when an inner planet lies between the Earth and Sun.

Mostly in the daytime, conjunctions occur or when the objects are beneath the horizon. When the objects are bright, daytime viewing is possible, such as a crescent Moon and Venus. However, if the objects are set below the horizon, then they won’t be visible. Conjunctions are ideal for public stargazing events as it really captures our attention, or just simply inspire newcomers and young astronomers to look up at the night sky.

Nowadays, with the abundance of technology in daily gadgets, such as mobile phones with cameras, celestial conjunctions are now easy to capture with a degree of accuracy, providing more people the chance to preserve the moment to be shared with family and friends or even on social media.

For those who would like to see conjunctions in the night sky, some of the fascinating phenomena are coming up over the next few weeks between the planets, stars, and the Moon. This month, July, on the 11th through 18th, Neptune lies close to the star HIP 116042 but will require you to have at least 7×50 binoculars or a larger or telescope. It would be mag. +7.2, which is slightly brighter than mag. +7.8 Neptune.