Constellation of the Month: Orion
Orion Constellation
Betelgeuse (Alpha Orionis): Last month we spoke about Aldebaran in Taurus. Well, this is another giant red star, but it plays in a superior league. Being located 520 light-years from us has a diameter 700 times greater than our Sun and is 10,000 times brighter than our "home" star. This star is a variable type one due that it expands and shrinks, a behavior common to many red giants and as a result it has a mean magnitude of 0.7, reaching sometimes 0.2 magnitude and having a period of 5.7 years. The name "Betelgeuse" means "shoulder" and this name is well suited because it reflects its relative position in the constellation.
Rigel (Beta Orionis): Again, this star has a name well suited to its relative location in Orion, because it means "foot". Rigel has a white-blue color and is a very hot star. Located about 900 light-years from us, has a diameter 50 times greater than our Sun and is 57,000 brighter than the Sun!. This means that it's burning its nuclear fuel at high-speed, so its live will be short, in astronomical terms, of course. Its magnitude is 0.3, so this is an example where the star "Alpha" of the constellation (Betelgeuse) is not as brighter as Beta.
Rigel is a double star, but we would need at least a telescope with a 150mm (6") aperture in order to split it because the great difference in magnitude; its companion star has a magnitude of 6.7 and is separated by 9.4 of seconds of arc.
The arch (Pi1..Pi6): This stars are interesting because observing them with your naked eye you can establish the limiting magnitude of the sky for a particular night. The respective magnitudes from Pi1 to Pi6 are: 4.7, 4.4, 3.3, 3.8, 3.9 and 4.7. If for example, you can't see Pi1 or Pi6 then don't expect to hunt all but the brightest Messier objects in that night.
Mintaka (Delta Orionis): If Rigel is out of reach as a double for our refractor, Mintaka (the more western star of the belt of Orion) is a very "easy" double. The main component has a magnitude of 2.4 and even at only 25x appears another component with magnitude 6.8. Both stars are separated by 53" seconds of arc (about 0.5 light years, so its rotation period can be as high as 1 million years). In fact, Mintaka is one of the most easy to split double stars in the sky with a telescope.
Sigma Orionis: This is a multiple system of stars. With our refractor we can observe up to 4 stars. The main component has a magnitude of 4, and the rest of components have magnitudes of 10, 7 and 6, being separated respectively by 11, 13 and 41 seconds of arc.
Lambda Orionis: Located in the "Head" of the Hunter, this is another interesting double. The main component has a magnitude of 3.7, and located only 4.4seconds of arc appears another component with magnitude 5.6. You will need at least 100x in order to split it, and don't hesitate in using higher magnification if you wish.
Iota Orionis: This one is more easier to split than Lambda Orionis. The main component has a magnitude of 2.9 and the another component, with magnitude 7.4 is located 11.4 seconds of arc apart. 100x is the best magnification to observe it.
Alnitak (Zeta Orionis): This star is the most eastern one in the belt of Orion. It is a triple star and the main component has a magnitude of 2. Separated by only 2.1 seconds of arc there is another component with magnitude 4.2, so you'll need at least 100x, or better yet 200x in order to split it. Located 57 seconds of arc there is the third component shining with only magnitude 9. To split it you only need about 40x or even less.
Theta 1 Orionis: See M42
M42 (Orion Nebula): There is an unofficial "top-ten" list of the most beautiful objects in the sky, and M42 is almost always the most voted in it, only second to Saturn. It's visible with the naked eye and a telescope reveals a fantastic view. Located 1,600 light-years from us, has a diameter of 50 light-years and it's an stellar nursery where several new born stars live, with ages of only from 10,000 to 100,000 years. One of this young stars is Theta1 Orionis.
Theta 1 Orionis, the Trapezium
Better known as "The Trapezium", Theta1 Orionis is a multiple system with six observable components, four of them relatively easy to observe. In fact, with only 40x you can observe components A, B, C and D (with respective magnitudes of 6.8, 8.0, 5.4 and 6.3, but in order to observe components E and F (with same magnitude 11) you will need really dark skies, because the theoric magnitude limit of a 90 mm aperture scope is 11.5. This implies an interesting observing challenge, so I'm planning a trip to the mountains in order to "hunt" these weak components. The challenge is not an easy one, but I would bet it can be done at 100x under excellent skies with averted vision and using very good eyepieces. Of course, if you get it, please notify me in order to publish it in these pages.
M78: After speaking about M42, M78 appears a bit less interesting. It is an small nebula located about 2.5 degrees northeast from Zeta Orionis (Alnitak)