Mercury is difficult to view with the human eye, but it may be seen using a telescope even during the day if you know where to look. When Mercury comes close to the Earth, a tiny disk may be seen, as well as phases (similar to the Moon's).
The best time to observe Mercury is when it is near the horizon in an area away from bright lights. It will appear as a crescent or half-moon. As you watch, it will gradually move upward into the morning sky until it is directly above you. Then it will begin to set again at sunset.
For most people, seeing Mercury is not easy because it passes quickly across the night sky. It only remains visible for a few hours at a time. But those who have looked with the proper equipment will know that it is worth watching because this planet is the closest to us outside of the Earth's own shadow.
Also, because it orbits so close to the Earth's shadow, some of its surface is always in darkness. This means that wherever you are on Mercury, there is a part that is never exposed to sunlight.
Finally, because Mercury has no atmosphere, everything on its surface is exposed to the influence of cosmic rays. These high-energy particles come from deep inside the Solar System and can damage electronic devices if they hit them.
Yes, Mercury is seen without a telescope since it is one of the five brightest planets. Mercury, on the other hand, is one of the five brightest planets and one of the most hardest to view. Mercury is the nearest planet to the Sun, and only from a few angles can Earthlings see it without interference from the Sun's light.
Venus is also visible to the naked eye, but it is dimmer than Mercury and difficult to find. From a dark location with no lights interfering, you should be able to see Venus as a yellow-white dot against the black background of night sky. It will appear low in the southeast just before dawn, getting higher as the day progresses. By mid-afternoon, it has risen above the horizon and by midnight it has set.
Mars is the next planet out from the Sun that can be seen with the unaided eye, though it is not easy. At its closest approach to the Sun (reduced distance of approximately 55 million km), Mars appears red and becomes brighter than the Moon. But it does not always show this at its closest approach - when it is on the opposite side of the Solar System from Earth - because we cannot see it then. Instead, it goes into hibernation, or martian winter. During this time, the atmosphere is cold enough to freeze water vapour into ice crystals that reflect sunlight back towards space, which causes the planet to go completely invisible.
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 bearer, Phoebus Apollo, and an even brighter body they called "Hemera" (meaning "red-hot"). Today, we know that these are just two faces of one world.
Modern telescopes have revealed many details about Mercury that were not known when it was first photographed by Mariner 1 in 1974. Scientists have found that it has a surprisingly complex surface with many large craters, some as big as 100 miles across. They also know that there is water under some of those craters!
You may have heard that Mercury has no axial tilt. This means that it orbits the Sun directly above the equator, like our Moon does. But this isn't true for all mercury sightings. If you see mercury around midnight, when it is right on top of the Sun, then it must be experiencing extreme axial tilt - more than 45 degrees! Because the Earth's axis of rotation is tilted by about 23.5 degrees, this means that half of mercury is facing up toward the sky and half is down toward the horizon.
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 is my teacher telling us that Mercury is a planet? He's not sure why it moved away from the Sun, but he thinks it might have an atmosphere. If you ask me, I think he is just having fun with words. I will say that it receives radio signals from Earth, which show that it has an iron core surrounded by a metal shell. It also has a day and night side. Although both are equally heated by the Sun, the night side is too cold for water ice or gas clouds like we see on Venus.
People have been talking about other planets for as long as they've been writing things down. The ancient Greeks used to call Jupiter "the king of gods and men" and Mars "the warrior god". In 1738, Isaac Newton proposed that all the Solar System's planets except Earth acted as giant balls of rock in close orbit around the Sun. He called this theory "ellipses". Today, most scientists agree that the other planets do indeed follow elliptical orbits, but they are not rocks rolling across the sky, but rather families of gases that circulate between the planets and their star.
Mercury cannot be seen by Hubble because it is too close to the Sun, the brightness of which would destroy the telescope's delicate sensors. Mercury has only been visible with a telescope since 1975.
Before then it was impossible to see with the unaided eye because it goes around the Sun every 48 hours and thus always shows the same face to Earth. Only when viewed through a telescope does Mercury's orbit around the Sun bring it out of sight each time it passes behind the Sun.
The reason for this is that astronomers use telescopes to look at objects beyond the limits of what we can see with our own eyes. Before the invention of telescopes, the only way to see far away objects was with your own two eyes. But there are some objects so distant that they are only visible as dots in the sky. For example, if you looked up at night with a light-sensitive plate you might see stars as points of light but you would never see planets or galaxies this way. To see these objects with your own eyes, you would need a very powerful telescope.
A telescope makes objects appear larger than they actually are and farther away than they are actually located.
Mercury is a tough planet to investigate in comparison to other planets. The speed necessary to reach there is relatively great, and its close closeness to the Sun makes maneuvering a spacecraft into a stable orbit around it challenging.
So far only one spacecraft has successfully visited Mercury, and that was NASA's Mariner 10 in 1975. It obtained early data on the composition of Mercury's atmosphere before losing contact with Earth.
Future missions are planned by the National Aeronautics and Space Administration (NASA). In addition to Mariner 10, they include MESSENGER, which was launched in 2004 and is currently orbiting Mercury; OSIRIS-REx, which is scheduled for launch in 2016; and BepiColombo, which will join Mercury Probe in 2019. Other countries have sent their own probes to study Mercury as well. They include the Soviet Union's MIG, France's SMART, and India's MOM.
The reason why visiting Mercury is difficult can be understood by thinking about how each planet was discovered. On Mars, we know that there is water under its surface from observations made by many different types of instruments on various missions over many years. On Jupiter, we know this from direct observations made by spacecraft flying through its clouds.