Mars Oppositions - 1995-2005
In positional astronomy, opposition is used to indicate when two bodies are on opposite ends of the sky when observed from a fixed point(usually Earth bound). A particular instance would be that two planets are in opposition when their ecliptic longitudes are 180° from one another.
A celestial body is said to be in opposition when it is in opposition to the Sun as seen from the Earth. When a planet is like this several things happen: that body is visible for most of the night. It will rise at sunset, culminate at midnight, and set at sunrise, it is at its closest point to Earth(perihelion), the portion of the body that is visible from Earth is totally illuminated(full), and the opposition effect( the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer) increases the reflected light from bodies with unobscured rough surfaces. Opposition can only occur with planets that are farther from the Sun than Earth(superior planet). The Moon is in opposition to the Sun during its full phase. When it is exactly in opposition, a lunar eclipse occurs.
Opposition is very helpful in determining the location of objects on the celestial sphere on a certain date, time, or observational location on Earth.
We have written many articles about opposition for Universe Today. Here’s an article about the distance of Venus from the Earth, and here’s an article about the distance from Earth to Mars.
If you’d like more info on opposition, check out NASA Science article about the approaching Mars, and here’s a link to NASA’s Lunar and Planetary Science page.
We’ve also recorded a series of episodes of Astronomy Cast about every planet in the Solar System. Start here, Episode 49: Mercury.
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