This week, Venus and Mercury will be visible in the early sky. Mars, Jupiter, Neptune, and Saturn will all be visible at night. Earth Sky released a comprehensive guide to viewing the planets, including information about Uranus (via WCVB).
Venus is the brightest object in the evening twilight, while Mercury is the brightest object after midnight. They can both be seen with the naked eye on a clear night without optical aid. In fact, ancient peoples used to watch these objects disappear one by one as they went through the phases of the moon. Today's astronomers use telescopes to see them as dots of light against the blackness of space.
Jupiter is the king of the planets and its enormous size makes it easy to see with the unaided eye even in daylight. It's located between Saturn and Mars and lies over 10th magnitude in the constellation Virgo. The other planets are too small or faint for the average person to see with the unaided eye. However, scientists have discovered many additional objects called "extrasolar planets" which are larger than Earth but probably less massive. Some of these may be able to support life and could be similar to our own planet in many ways but others may be very different from Earth. Scientists are still debating what role, if any, these objects may have played in creating us humans.
The planets Venus, Mars, Jupiter, and Saturn will be visible in the sky tonight. Meanwhile, Mercury, Uranus, and Neptune will be visible, but you will most likely require a telescope to see those three planets. Pluto is no longer considered a planet, so it won't be visible tonight.
Venus is the brightest object in the evening sky after the Sun. It can appear as a golden-yellow star if it rises before sunset or as a white light if it sets after midnight. If you are able to see Venus without a telescope, you should be able to see it with the naked eye, although it will be quite dimly.
Mars is the next-brightest object in the evening sky after Venus. It appears as a red star if it is rising before sunset and as a white one if it is setting after midnight. If you have binoculars or a small telescope, you should be able to see Mars even though it is not very bright.
Jupiter and Saturn are the two largest objects in the night sky after the Moon and Earth. They appear as the four brightest stars in the west just before dawn. Although they do not change position relative to other stars, they are often called "wandering" stars because they seem to wander across the sky from night to night.
Unfortunately, you will never be able to view all eight planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune – in the night sky at the same time. Uranus and Neptune are not visible with the naked eye and need the use of a telescope. The other seven can be seen with the naked eye, but they are so far away from the Earth that only certain areas of the sky contain them all at once.
From around 300 million years ago until about 75 million years ago, when conditions were right, Mars may have had oceans covering much of its surface. These may have been filled with water, as well as containing other elements such as silicon and oxygen. Some scientists believe that if enough evidence is found, it might be possible to find signs of past life on Mars today.
In 1610, German astronomer William Herschel discovered four more planets then known to science: Mercury, Venus, Mars, and Jupiter. He was the first person to observe each of these planets except for Mercury. Today, we know that there are actually hundreds of millions of planets in our galaxy alone. Many astronomers believe that there could be billions of planets in our galaxy and others like it. We just haven't reached yet to find out.
The majority of the planets in the solar system are visible with the naked eye, with just Neptune and Uranus eluding unaided observers. However, the five "bright" planets, Mercury, Venus, Mars, Jupiter, and Saturn, seldom share the night sky at the same time. From Earth they appear as luminous points of light with other stars appearing around them in the sky. Because of this reason, these objects are called "wanderers" or "stars".
Even though they are very bright objects most people cannot see them with their naked eyes under normal circumstances. The human eye is not designed to see faint objects such as planets, so experts recommend using a telescope to look at them.
From about 50 years ago to the early 1990s, astronomers used photographic plates to record images of the night sky. They then analyzed these photographs looking for changes in the positions of celestial objects. This method revealed many new objects such as galaxies far beyond our own galaxy, quasars (extremely distant active galactic nuclei), and supernovae.
Since 1995, scientists have used digital cameras to take pictures of large areas of the sky and computer programs have been able to analyze these pictures in order to find interesting objects such as new planets or even new galaxies. So far, these surveys have revealed many new objects including several planets that were previously unknown to exist.
Which planets can be seen with the naked eye from Earth? For much of the year, Mercury, Venus, Mars, Jupiter, and Saturn are visible. Neptune and Uranus are not visible, and the eighth planet in our solar system is, of course, Earth. Mars, Mercury, and Venus can be visible at dawn and dusk during this period. Jupiter and its moons can be seen in the night sky with the aid of a telescope.
Earth's neighbor, Venus, can often be seen as a bright light in the morning or evening sky. From Venus, the Earth looks unusually small, perhaps half the size of the moon, because it is so far away. Because of this distance, the features on Earth appear extremely large compared to those on Venus. However, even though Venus appears larger than Earth from such a great distance, it is still quite a small world for its size: About 442 miles in diameter, or 740 km. The next largest planet, Mars, is about 64% of Earth's diameter.
Mercury, the closest planet to the Sun, cannot be seen with the unaided eye but which is visible as a faint crescent when viewed through a good telescope on a clear night. It takes over eight months for Mercury to orbit the Sun due to its close proximity. During that time, it goes from being invisible outside of a telescope to becoming completely illuminated by the Sun's rays.
Mercury, Venus, Mars, Jupiter, and Saturn are referred to as the "bright planets" because they are the five brightest planets visible to the naked eye. These planets can sometimes be seen soon as it starts to turn dark. At times, they are only visible late at night. They are called "morning stars" because they are the first ones visible in the morning sky.
These planets appear bright because they are very close to Earth and reflect sunlight back to us. The further away a planet is from us, the fainter it appears. Even though they are far away from us, they still rotate around our star every day. When viewed from Earth, these planets look fixed in place but this isn't true; they travel across the sky at high speeds.
Mars is the closest planet to Earth and can often be seen with the naked eye. It becomes visible after sunset and before sunrise when light from the moon and stars doesn't reach the earth's atmosphere to interfere with viewing of Mars. On an clear night with no clouds or light pollution, you should be able to see several moons hanging in the sky along with Mars and Jupiter.
Jupiter is by far the largest planet in our solar system and can be seen with the unaided eye even in urban areas. It's also the most distant planet from Earth, which means it takes 12 years for it to make one full rotation around our star.