March 2014 is a great time for greatest elongations. I'm talking about Mercury and Venus being at their highest above the sun in the morning sky. Continue reading →
¡SkyCaramba! Weekly astronomy blog for the week ending March 8, 2014
March 2014 is a great time for greatest elongations. I’m talking about Mercury and Venus being at their highest above the sun in the morning sky.
The angle between an object and the sun as we see them is called elongation. A planet that’s rising as the sun is setting has about 180° of elongation. After all, it’s about halfway around a 360° dome. If the planet’s high overhead at sunrise or sunset, it’s about a quarter of the way around and so it has about 90° of elongation. An object with 0° elongation could be between us and the sun. It could also be on the other side of the sun. The moon has 0° elongation during a total solar eclipse.
Venus and Mercury never get close to 180° elongation. Instead, they reach what’s called greatest elongation. That’s when they’re at the greatest angle from the sun before turning around and going the other way. Mercury will be at ...