Tag Archives: Mercury

Observing the Inner Solar System: Mercury and Venus

When guests visit the local observatories, staff astronomers always look to impress them with great views of the Moon, Jupiter, Saturn and Mars when any of these worlds are observable. The wealth of detail visible through each facility’s telescopes can awaken the sense of awe within children and adults alike. What child hasn’t marveled at the Moon’s vast craters? Who hasn’t watched the parade of Jupiter’s Galilean moons orbiting this gigantic planet and not thought about Galileo’s first view of this phenomenal sight? We sky interpreters love to hear the oohs and aahs as folks get a glimpse of Saturn’s magnificent rings for the first time. And when dust storms on Mars don’t spoil the view of this desert-like world, who can’t help but wonder if life may exist beneath its surface? Any night amateur astronomers can introduce casual stargazers to these magnificent worlds is a wonderful experience.

However, while the afore-mentioned objects get most of the glory, there are two inferior planets of our solar system that are often neglected. No, they do not have any neuroses. Inferior is an astronomical term meaning these planets orbit between the Sun and the Earth. I’m referring to Mercury and Venus. Consequently, they do not stray far from the Sun in the sky from our Earthly perspective. Examine this brief video which explains what we observe. Whenever Mercury and Venus appear above either the eastern or western horizon these events are called elongations. Mercury can appear no more than a maximum of 28 degrees away from the Sun, while Venus can appear no more than a maximum of 48 degrees away from the Sun. Elevation above one’s horizon varies from one elongation to another.

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Transit of Mercury: A Unique Astronomical Event November 11, 2019

Venus and Mercury transits occur when these worlds, which orbit between the Earth and the Sun, can be seen to pass directly in front of the solar disk and transit across the face of our star. Why don’t we experience a transit of Venus or Mercury every time they pass between the Earth and the Sun (called inferior conjunction)? It all has to do with the orbits of these planets and our ever-changing viewing angle. Most of the time Venus and Mercury pass above or below the solar disk as seen from the Earth. This concept is simply stated here, but it took the greatest astronomical minds of the past to solve this great mystery. The process took much observation, dedication and deduction to determine the solar system design and the celestial mechanics that govern its motion.

Venus transits are rare astronomical events. They always occur in pairs, eight years apart. We last experienced transits of Venus in 2004 and 2012. Their immediate predecessors occurred back in 1884 and 1882. And the next pair won’t be until 2117 and 2125!

However, another planet can transit the Sun—Mercury. Though not as rare as Venus transits, transits of Mercury occur 12-13 times per century. The last one occurred on May 9, 2016 and it was observed in its entirety locally. The Mercury transit prior to that occurred on November 8, 2006, but in Southern New England we were clouded out. Unfortunately, the next one visible here after the upcoming November 11 event won’t be until May 7, 2049.   

Continue reading Transit of Mercury: A Unique Astronomical Event November 11, 2019