Neptune in Conjunction
Published on Feb 10, 2008 at 6:28 pm.
2 Comments.
Filed under astronomy, planets.
According to my Observer’s Handbook, Neptune will be in conjunction with the Sun in less than two hours. So, I thought that I’d take a moment to explain what we mean by the terms conjunction and opposition when we are talking about planets. For this discussion, I’ll focus on superior planets, which are defined as those planets farther out from the Sun than we are. Inferior planets are those closer to the Sun than we are. So, that means that Mercury and Venus are inferior planets to Earth. The rest, though, (Mars, Jupiter, Saturn, Uranus, Neptune) are superior planets.
The farther from the Sun that a planet orbits, the longer it takes to go around. So, that means that Earth orbits the Sun faster than the superior planets. Thus, Earth is sometimes on the same side of the Sun as the superior planet, and sometimes on the opposite side of the Sun. The terms conjunction and opposition refer to the orientation of the planet and Sun as seen from Earth. When two bodies are in conjunction, that means that one or both of them have been moving and the conjunction is the closest that they are going to be to one another. In other words, they have been getting closer and after conjunction are getting farther apart.
For a superior planet, conjunction occurs when the planet is on the opposite side of the Sun than Earth. Since the planets orbit the Sun in nearly the same plain, then conjunctions will always be very close to the Sun in the sky. In fact, if you could dim out the Sun, the planet will occasionally be directly behind the Sun. But, the orbits are not exactly in the same plain, so sometimes the planet would appear slightly above or below the Sun in the sky at conjunction. That is, it would appear that way if the Sun were dim enough to see past it!
When Earth and the Sun are on the same side of the Sun, the planet appears nearly opposite of the Sun in the sky. The planet is then said to be in opposition. Since Earth moves much faster around the Sun than Neptune, in six months Earth will be on the opposite side of its orbit from where it is now, but Neptune will have not moved very much. So, opposition will occur in just over six months, on August 15.
As for observing the planets, when they are in conjunction, forget it! The Sun is simply too bright to see past. Opposition, however, is another matter. That is also about when the planet and Earth are closest, making the planet appear largest in the telescope. Also, the planet is opposite the Sun, so it rises at about sunset and sets at about sunrise. That means it is up all night at opposition. Conversely, at conjunction, the planet is behind the Sun, so it rises at sunrise and sets at sunset.
For inferior planets, those that orbit closer to the Sun than Earth, there is never an opposition because the planet can never be in a position on the far side of the Earth than the Sun. But, they can have two conjunctions, one when they are between Earth and the Sun, and once on the far side of the Sun. In this case, we call the conjunction between Earth and the Sun an inferior conjunction and the conjunction on the far side of the Sun a superior conjunction.
-Astroprof
Astroprof’s Page » Saturn at Opposition on February 24, 2008 at 4:40 pm: 1
[…] About a week and a half ago, I wrote about Neptune being in conjunction with the Sun. That was when Neptune was on the opposite side of the Sun from Earth. Today, I am writing about another planetary alignment. Saturn is in opposition. That means that Saturn is on the opposite side of the sky from the Sun, as seen from Earth. Another way to look at this is from outside the Solar System. There, you would see Saturn and Earth on the same side of the Sun, forming a line with the Sun, Earth, and Saturn. […]
Pam on May 16, 2008 at 1:57 pm: 2
What does this mean???