Solar System Magnitude Scale
Magnitudes of the Sun, Moon, Planets, and More!
There are ten natural solar system objects you can see without optical aid. You may be surprised at what is on the list and what is not, and the order in which they rank! Magnitude is the number used to determine how bright an object is. The lower the number in magnitude, the brighter the object shines. The dimmest object that can be seen with the naked eye is anything around 6th magnitude. Here are the top 10, in order from brightest to dimmest:
- The Sun. No surprise here. The Sun shines at magnitude -26.7. Technically, the Sun can't even be looked at without optical aid when it is at its brightest. Sunrise and sunset are the best times to view our closest star.
- The Moon. The moon varies in brightness depending on what phase it is in. At its full phase when it is the brightest, it tops out at magnitude -12.6, and in a crescent phase it is about a -6.
- Venus. As with all the other solar system objects, Venus varies in brightness depending on a number of factors, including how close it is to Earth and what phase it is in. Venus can shine as brightly as -4.7 and is frequently referred to as the Evening Star or the Morning Star.
- Mars. Mars is the second closest planet to Earth after Venus, but it does not often reach its maximum magnitude of -2.9. Its reddish-orange hue helps to distinguish it from other planets.
- Jupiter. This gas giant is often brighter than Mars and at its maximum shines almost as bright, at magnitude -2.8.
- Mercury. Surprise! The rarely seen Mercury shines more brightly than Saturn at its best. Mercury can reach -1.9 magnitude but because of its position near the Sun, it does not get to be seen high in the night sky. Its brightness is often offset by the fact that you are viewing the planet near sunrise and sunset.
- Saturn. Saturn, which is stunning in a telescope sporting wide rings, is also a fairly easy catch without optical aid. At magnitude 0.7 it outshines most stars.
- Ganymede. Ganymede is the largest moon of Jupiter. Keen eyes can spot it circling Jupiter when the satellite is at its brightest, approximately 4.6 magnitude.
- Vesta. This asteroid, which was the fourth asteroid to be discovered, can reach magnitude 5.4 at its closest approach to Earth. Because it does not have a brighter sky marker, as Ganymede has with Jupiter, it is best to watch for it a couple nights in a row to see which dim "star" in the area appears to slowly move.
- Uranus. The seventh planet from the Sun appears at magnitude 5.5 at its best. Uranus is best picked up with the naked eye after first pinning down its location with binoculars or a telescope. It has a disk instead of a pinpoint image through an optical device and may even appear faintly bluish green.
Ceres is a bright asteroid but at magnitude 6.7, it would be a real trick to pick out with the eyes alone. Neptune at magnitude 7.7 and Pluto at 13 require optical aid. (Pluto, in particular, requires a large telescope.) There are transient solar system objects that occasionally appear bright enough to be seen without optical aid, such as meteors or comets.
