By the end of the month, you might be able to see Mercury with binoculars in the morning twilight, low in the east-northeast about an hour before dawn. On July 4, Mercury will be at its greatest elongation, 22 degrees from the sun, however its apparition will be unfavorable for watchers in the mid-northern hemisphere. Only those living near the Arctic or Antarctic circles will be able to see it during this time.
Its surface is covered by a thin veneer of rock and soil called regolith that was once molten lava. Because of this history, many features on Mercury can still be seen with modern telescopes: craters, valleys, even parts of a continent.
Mercury has only half as much air as Earth does, so there are very few clouds there. The atmosphere is made up of sulfur dioxide gas that spreads out from the sunlit side of the planet into space. This gas creates a global magnetic field that protects the planet from most radiation from outside sources.
The average temperature of Mercury is 450 degrees Fahrenheit (230 degrees Celsius). Most of the time, the entire surface is heated by the sun to more than 500 F (260 C), but every now and then portions of the planet's surface freeze over. These frozen areas are called "mercurial deserts". The only place on Mercury where water may exist in liquid form is in two small volcanic regions that remain warm enough for some activity all year round.
If you monitor it between July 20th and August 9th, you'll notice Mercury wandering, offering strong evidence that it is, in fact, a planet. Infrared images (center, 2007) can be rebuilt, or the Messenger mission can fly to Mercury and photograph it directly (right).
Why do we know this? Because astronomers have been able to see signs of activity on Mercury for more than 100 years. The first observations were made by Asaph Hall, an American astronomer who studied Mercury using telescope surveys. In 1877, he reported finding markings that appeared to change shape over time. These changes could only have been due to Mercury having an internal source of heat, which is what causes our planet to swell and shrink as it orbits the Sun.
More recently, NASA's Mariner 10 spacecraft discovered large deposits of water ice near the north pole of Mercury, providing further evidence that it has an internal source of heat.
So, is there anything else about Mercury that makes scientists wonder if it's a planet? It takes 89 days to orbit the Sun, so it must be close to Earth in size. But it travels much farther away from the Sun every cycle, so it must be larger than Earth.
The most accurate way to measure distance is with parsecs (or pc), but because Mercury is so far away from the Sun, even the closest telescopes cannot resolve its image completely.
Mercury was detected at wavelengths of 3.75, 4.75, 8.6, and 12 microns before, during, and after the inferior conjunctions of September 29, 1969 and May 9, 1970. The average temperature on the dark side is 111 deg +-3 deg K. On the light side, the average temperature is 48 deg +-5 deg K.
During these periods of observation, the planet appeared black because there are no clouds or other particles to reflect sunlight like Earth's atmosphere does. Instead, there is a thin layer of carbon dioxide between the surface and the sky. When sunlight hits this gas, it bounces back into space.
Carbon Dioxide has two states of matter: a solid (ice) and a gas (air). Carbon Dioxide exists as solid ice in all the planets except Earth, where it is a gaseous molecule. CO2 molecules are very stable and don't easily decompose; they can be found in many different forms within the galaxy, including rocks, clouds, and bodies such as Mercury.
The average distance between the Sun and Mercury is 147 million km (92 million miles). At this distance, the sun emits about 1020 W/m2. This is more than enough energy to evaporate water from the surface of Mercury, but not enough to heat it up significantly.
The Transit of Mercury When Mercury passes in front of the Sun, it appears as a small black dot silhouetted against the Sun's disk. The most recent Mercury transit occurred on November 11/12, 2019. The next one will take place on November 12/13, 2032.
It is not possible to see Mercury's shadow crossing the Earth, because it crosses only the portion of Earth that lies in between the Sun and Mercury. However, scientists can study events during a transit by using information from other sources. For example, observers in places where it gets dark early can use this fact to estimate when and where Mercury is passing over their heads. Also, scientists use data from probes orbiting Mercury to learn more about its interior structure and composition.
Data from NASA's MESSENGER spacecraft indicate that the area near the center of Mercury is very hot. This region may be a large volcano that has been active recently. Data from the European Space Agency's (ESA's) Mercury Magnetometer (MAG) instrument reveal that there are strong and variable magnetic fields everywhere on the planet except at the equator. The cause of these fields is still being investigated by scientists. They may be generated by currents flowing within the planet itself or they may be due to interactions with Jupiter and Venus.
In addition to the two transits mentioned above, Mercury also passes behind Earth every 878 days.
It will be visible from the majority of the Earth's surface. From South America, eastern North America, and far-western Africa, the whole trip is visible. Mercury's most recent transit occurred in 2016. The next one will not happen until 2032.
People around the world will have a chance to watch as Mercury passes between Earth and the Sun today (Tuesday). The planet will appear to slide across the face of the star-studded sky as it orbits towards the center of our Solar System every 88 days.
This event is called a "mercurial transit" and it can only happen when Mercury is close to Earth and at least partly inside the Earth's orbit. Because of this, we only get to see one every 12 years or so. Today's transits are visible from pretty much everywhere on Earth apart from North America.
You need a clear view of the night sky to see Mercury crossing the Sun. This happens approximately at 11:00 a.m. EST (8:00 a.m. PST). However, if you're in an area where there is some kind of activity happening on the ground (such as people, cars, buildings) then you could miss out on seeing Mercury because it is hidden behind these objects.
Mercury is our solar system's nearest planet to the Sun. It is only seen in the early morning, soon after dawn, or after sunset since it is so near to the sun. In fact, ancient Greek astronomers once thought Mercury was two distinct objects. They called the bright object "Phoebus" after its Roman name.
Today, most people see Mercury when it is low on the horizon after dusk. It can also be glimpsed during a lunar eclipse. But even from far away, it looks incredibly small and dim. The closest approach that Mercury makes to the Earth is 453,000 miles (741,000 km).
It used to be possible to see Mercury with the unaided eye during an evening twilight. But this has been known to happen only three times in the last 150 years - in 1882, 1932-33, and 1949. On each of these occasions, reports of seeing Mercury with the naked eye came from parts of the world where there had been no previous indication that it was visible from that location. So it seems these observers were actually seeing something else - probably Venus - very close to the position where Mercury should have been visible.
The next opportunity to see Mercury will be on May 9th when it rises around 4:00 a.m. PDT (7:00 a.m. EDT), just as the Sun begins its daily descent toward the west.