So, where is Mercury?
Published on Feb 2, 2008 at 8:53 am.
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Filed under Mercury, observing, planets.
Over the last couple of weeks, I’ve posted several things about the planet Mercury. So, you might be tempted to ask, “Can I see Mercury in the sky tonight?” Unfortunately, the answer is, “Probably not.”
In the image below, I show the view to the western sky right at sunset. The Sun is on the horizon, and Mercury appears just a hand’s width above it in the sky. By the time that the Sun is low enough for the sky to be dark enough to see Mercury with your naked eye, it will be too low. This image is created for here in Texas. Much farther north, or for observers in the southern hemisphere, the geometry is even worse. Mercury will appear even lower in the sky.
Remember that Mercury orbits the Sun much closer than does Earth. So, that means that Mercury always appears fairly close to the Sun, as seen from Earth. That makes it hard to see. Only a few times per year does Mercury appear far enough from the Sun to be easy to see. Worse, Mercury has a very elliptical orbit, and it is now near the closer point in the orbit to the Sun, so that makes it appear even closer to the Sun in the sky. In the sky schematic here, you see Neptune near Mercury in the sky. That does not mean that Mercury and Neptune are actually near one another in space. Rather, Mercury is close to us, and Neptune is clear across on the far side of the Solar System. You have to look past the Sun to see Neptune. Since Mercury appears near the Sun, you look past Mercury to see Neptune. Below, I have a graphic of the relative positions of the planets of the inner solar system, as it would be seen from far above the north pole of the Sun.
Also, don’t wait for Mercury to be in a better position to view. It will be some time before that happens. Right now, Mercury is moving towards inferior conjunction, the position between Earth and the Sun. That means that Mercury will steadily become even closer to the Sun in the sky, making it even tougher to observe. So, you’ll have to be content with looking at pictures of Mercury sent back by the MESSENGER spacecraft.
-Astroprof
Images created using Starry Night Enthusiast
