Science Snippet:

Explore Mercury

Mercury (top) and Venus (bottom) align with the moon by Paranel Observatory. Author: ESO/Y. Beletsky. CC BY 4.0

Mercury is a difficult planet to observe. It is the smallest planet and it is currently over 121 million miles away. But that is not why Mercury is hard to see. While Mercury may be small for a planet, it is not that small. It is slightly larger than the moon. In our sky, Mercury is often brighter than all but the brightest stars. Mercury is hard to observe because it is much closer to the sun than we are. Venus is also closer to the sun but it is quite easy to find. Venus is much further from the sun than Mercury is. While Venus is closer to Earth than it is to the sun, Mercury is closer to the sun than to Earth. This means that Mercury travels through our sky with the sun, never rising long before the sun or setting long after it.

The best time to try to find Mercury is when it is at greatest elongation. At these times, the Mercury is as far from the sun as possible in our sky. To visualize this, imagine the solar system as a clock with the sun in the center of the disk. If the Earth was at the 6 o’clock position, Mercury would be at either the 3 or 9 o’clock position when it is at greatest elongation.

Not all greatest elongations are good times to find Mercury, however. Mercury has the most elliptical orbit of any of the planets. This makes Mercury’s actual distance to the sun (as opposed to its distance from the sun in our sky) vary considerably. At times when it is closer to the sun, it will appear fairly close to the sun from our point of view, even at greatest elongation. But if a particular elongation is not very good, there will be another elongation fairly soon. Mercury orbits the sun every 88 days so there are either six or seven elongations every year. Although Mercury’s speedy orbit produces many elongations every year, it also has a drawback. Each elongation lasts only a few weeks at most. At the end of this article, I’ll include a list of upcoming elongations of Mercury.

Mercury shows phases like Venus but its phases are harder to see. Some people have seen Mercury’s phases with binoculars, but a small telescope greatly increases your chances of seeing them. Even with a telescope, Mercury’s phases can be difficult to see. Mercury is always near the horizon. This means that Mercury is shining through more air compared to an object that is higher in the sky. This can make Mercury appear out of focus.

Mercury is currently moving further away from Earth. It will reach its furthest point at the beginning of July when it will be over 123 million miles away. Using the travel method I’ve discussed in other articles, we could cover all of Earth’s land, the Pacific Ocean, and part of the Arctic Ocean before we had covered 123 million miles. This September, Mercury will be much closer to Earth at only 58 million miles away. Occasionally Mercury can even be the closest planet to Earth. This only happens when both Venus and Mars are at their furthest points from Earth in their orbits.

Mercury will be at elongation on the following dates. Usually, you can find it a few days before and after elongation as well. Look for it about half an hour before sunrise for morning appearances or half an hour after sunset for evening appearances. It will be near the horizon in the area of the sky lit by the sun.

  1. July 30, 2023: Evening (Very low)
  2. September 24, 2023: Morning
  3. December 9, 2023: Evening (Very low)
  4. January 8, 2024: Morning
  5. March 25, 2024: Evening
  6. May 15, 2024: Morning (Very low)
  7. July 13, 2024: Evening (Fairly low)
  8. September 7, 2024: Morning
  9. November 21, 2024: Evening (Very low)
  10. December 23, 2024: Morning