This week in Spacewatch we delve into some extreme skywatching targets. The Northern Hemisphere's current evening sky contains the brightest planet, the most luminous star known, the largest star, the most colorful star and finally the most distant object that can be seen with the naked eye.

All but one of them is also visible from parts of South America and Australia.

These are five objects that present a range of viewing opportunities, from the absolute easiest naked-eye skywatching to some that requires a telescope. In truth, we've gone over the edge: one object is not even visible from Earth in optical wavelengths (can you guess which one?); we've supplied a Hubble Telescope picture of it.

See how many of these extreme objects you can locate.

Astronomers are sometimes asked whats the largest known star? The answer to this question can be found within the constellation of Auriga, the Charioteer.

Auriga can be seen emerging from above the east-northeast horizon after 10 p.m. local daylight time. The Greek and Roman legends made Auriga a famed trainer of horses and the inventor of the four-horse chariot. However, the most ancient legend had Auriga as a goatherd and patron of shepherds. The brilliant golden yellow Capella was known as "The She-Goat Star." A nearby triangle of fainter stars are her kids.

One of the three kids is Epsilon Aurigae, a so-called eclipsing binary star. Here, two stars revolve about their common center of gravity over a period of 27 years. When the edge of the dark and much larger companion grazes across the front of the smaller, brighter star, Epsilon appears only half as bright.

This eclipse lasts a full year. The most recent was in 1983, the next in 2010.

The brighter of the pair is a supergiant star (called Epsilon Aurigae A), about 3,300 light years away and 60,000 times more luminous than our Sun. But it is the dark "ghost" companion that is believed to be the largest, coolest, and most rarified star known. With an estimated diameter of 2.4 billion miles, it would fill up much of the solar system out to beyond the orbit of Saturn!

To put this into a size perspective, imagine a model of the Sun that's the size of a soccer ball. On that scale, the larger star (Epsilon Aurigae B) would be a globe that measures nearly one-third of a mile (more than half a kilometer) across.

On that same scale, our puny Earth would be no larger than a sesame seed.

Scientists aren't sure of their explanation of the two stars. It's possible that we are not looking at a dark companion star at all, but rather a tremendous cloud of interstellar dust. But how could such a cloud maintain itself as it orbits around a massive supergiant star such as Epsilon Aurigae A?

Back in 1988 it was proposed that in reality, there might actually be a pair of less luminous and cooler dwarf stars that in turn are enshrouded by a vast, elongated cloud of dust. The two dwarf stars orbit each other, while in turn orbiting about Epsilon Aurigae A every 27 years. But how these supposed dwarf stars might generate the dust is a complete mystery, and if this hypothesis is correct it would make the Epsilon Aurigae system with its dual dwarf stars and massive dust cloud -- unique among any known star system in our galaxy.