Beginner’s guide to Orion


By Tom Burns - Stargazing



One of the holiday season’s astronomical ironies is that many much-anticipated telescopes end up under trees, but few of them get used until May. It’s hard to point a ‘scope when your feet are frozen to the ground.

This winter is complicated by the lack of bright planets in the evening sky. Prime telescope objects like Jupiter and Saturn are setting in the southwest. Of the autumn planetary spectacular, only Uranus and Mars remain.

Uranus will look like a tiny aquamarine dot if you can manage to find it. Mars is easy enough to find. Look southwest for a bright orange-yellow star.

However, Mars has faded from its autumn glory. At almost 80 million miles away, the 4,000-mile-wide planet has shrunk to, yes, another dot somewhat larger than Uranus.

Of course, there’s always the moon, but the fascination of its craters and flat, gray plains, called maria, soon fades.

Carefully plan your stargazing session to maximize your observing pleasure in winter. One technique is the time-honored method of “constellation mopping.” Take a familiar star grouping and work your way through it.

An ideal place to start is the constellation Orion, which dominates the winter sky. That fact makes it an excellent starter constellation for all you newbies out there in telescope land. Furthermore, even the smallest of “department-store” telescopes will show a few objects in Orion.

Let’s find it first. During late December, look southeast for a bright, vertical rectangle of four stars.

The rectangle stars that outline Orion’s body are bright enough to have been named by ancient Arab astronomers. Bellatrix (the Amazon Star), forms Orion’s shoulder on the right. Betelgeuse represents his shoulder to the left.

Saiph (“sword”) is Orion’s left foot, which makes no sense unless Orion had an accident with his weapon. Orion’s right foot is called Rigel.

Almost at the rectangle’s center are three brilliant stars in a horizontal row — Orion’s belt. Hanging from the belt is Orion’s sword.

Orion’s left shoulder has a name worth pausing over. “Betelgeuse” may be an extremely corrupted form of an Arabic expression that means “the armpit of the giant.”

Betelgeuse is a red supergiant, a star in its death throes. As a result, it has expanded to an incredible size. Although its mass is only 20 times that of our sun, its volume is more than 160 million times greater. For that reason, Betelgeuse is often called a “red-hot vacuum.”

You are looking at a star as large as the diameter of Earth’s orbit around the sun — 200 million miles wide. It has lived its short, 100-million-year life burning hydrogen at a prodigious rate. It has now swelled to enormous size in preparation for its death in a mere million years or so.

Single stars are much too far away to look like anything more than a point of light in a telescope. However, a quick look at Betelgeuse in a telescope or binoculars will help bring out its reddish hue.

Rigel (“left leg of the giant”), is, yes, the left leg of Orion, putting it at the lower right as we look at him. It is a white supergiant, about 50 times as big as our sun. It is the seventh brightest star, shining with an intrinsic brightness of nearly 60,000 times the sun.

Rigel and Betelgeuse represent the beginning and the end of the life of stars much more massive than our sun. Rigel has just begun its life as a supergiant star. Give it 100 million years or so, and it will become like Betelgeuse, a bloated dying star.

The reason it looks fainter than the brightest star in the night sky, Sirius, is that it is a lot farther away.

Make the comparison yourself. Using Orion’s belt stars as pointers, look down and to the left. Sirius should be scintillating close to the southeastern horizon. The nighttime sky’s brightest star is about 8.7 light-years away. It shines with an intrinsic brightness of only 20 times the sun.

Rigel shines 30,000 times brighter than Sirius, but Rigel is almost 100 times farther away at 864 light-years distant.

Most of the good telescope objects in Orion are clustered around Orion’s belt stars.

The first object to look for in a telescope is the multiple star system called Sigma Orionis. First, find Alnitak, the left-most belt star.

Sigma, the naked-eye star just below it, should split into three stars at high magnification. The brightest star in the trio is called Sigma AB. AB is really two very bright and massive stars orbiting each other so closely that you cannot split them in a telescope.

Nearby, Sigma D has a distinctly reddish glow. Sigma E is a bit farther from D than D is from AB. You are looking at a system of five stars, two of which you cannot see, that are all orbiting each other in an intricate cosmic dance.

Two of the stars in the belt are also multiple star systems. Look for single, dim companions next to Alnitak and Mintaka, the right-most star in the belt. Whether you can see them or not depends on the clarity of the sky and the size of your telescope.

Below Alnitak and Sigma and perpendicular to the belt is a vertical line of stars called the Sword of Orion. The sword is one of the best binocular objects in the heavens.

Near the bottom of the sword is the most beautiful object to observe with a small telescope —the Great Orion Nebula. This Great Nebula is easily visible with binoculars as a bright fuzzy patch.

A telescope reveals complex swirls of glowing hydrogen gas. Look for a complex fuzzy cloud, a glorious mass of glowing hydrogen in which stars are born. At high magnification, the four stars in a rough square at the nebula center are called the Trapezium. These stars are newly born out of the hydrogen gas that surrounds them.

Orion holds his shield before him, and above his head, he brandishes his upraised club. He is poised to do battle with Taurus, the Bull. Follow the belt stars up and to the right, and you will see the V-shaped head of the Bull.

Keep going up and to the right, and you’ll see a small cluster of six stars perched on Taurus’s shoulder. The Pleiades, or “Seven Sisters,” is another excellent binocular object.

In practically every culture on Earth, Orion has been called a hunter or warrior. North American Indians revered him as a great hunter of bears.

He predates the classical Greek civilization to the agricultural and even hunting cultures that preceded it. For them, he was a kind of sky calendar. When he rose at dawn, it was taken as a sign of approaching summer and in the evening as a sign of winter. When he rose at midnight, it was time for the grape harvest.

Later, the Greeks thought of him as the son of the sea god, Poseidon.

He makes the common mythological mistake. He falls in love (or, more accurately, in lust) with the Seven Sisters, the Pleiades. The gods lift Orion into the sky, where the Greek deities seem to store all the characters they find annoying.

My sympathies go to the Seven Sisters. The gods also put them in the sky, where Orion must pursue them forever.

If you have difficulty finding these objects, perhaps the person who gave you the telescope forgot to provide you with a good set of star maps. I’d recommend Guy Consolmagno’s “Turn Left at Orion.” With it and a telescope of practically any size, you’ll find plenty to see.

I know that many of you will depend on computer control to help you find sky objects. So be it.

However, if you learn the sky with a star map and your own blessed eyes, chances are that you will retain that knowledge and pass it on to the next generation. After all, humans have done since the beginning of our time on the planet.

Thus, here is my holiday gift-giving guide for next year: That you will brave the cold and dark, your heart and mind overflowing with joyous intimacy, to share a velvet-dark sky, filled with stars, with someone you love. In the end, aren’t your time and your love the greatest Christmas gifts of all?

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.