Slow Down And Watch Orion Rise

Earth’s spin speed varies according to latitude — fastest near the equator and slower at the poles. NASA with additions by the author

You’re spinning at something like 750 miles an hour (1,200 km/hr) as you read this. That’s approximately how fast the Earth rotates at mid-northern and mid-southern latitudes. At the equator it rotates even faster at around 1,000 miles per hour, while at the poles the speed drops to zero. We have no sensation of movement because everything in our environment from tables to trees is traveling at exactly the same rate. This makes it look like everything is standing still.

The same happens in an airplane or car. Once the vehicle reaches a steady speed everything in it travels at that speed. Cups and magazines remain in their places. The next time you fly in a plane close your eyes when you’re at cruising altitude, and you’ll have no sensation of movement only vibration from the air and engines. Of course if the plane suddenly accelerated or decelerated, we’d immediately experience the change in velocity and unattached objects would slide off the tray tables.

The Earth silently spins once every 23 hours and 56 minutes in relation to the stars. This approximately 10-minute time exposure reveals that spin in the motion of stars upward across the field of view of the camera. Earth’s rotation causes a star at the eastern horizon to rise at the rate of about 1° every 5 minutes. Bob King

Thankfully, Earth rotates at a nearly constant speed, neither accelerating nor decelerating except in exceedingly small amounts due to tidal effects with the moon and large earthquakes. In other words I can count on my teacup staying put. But there is a sure-fire way to experience our planet’s spin and that is to watch a star rise or set.

One of the brightest, easiest groups to watch rise is Orion the Hunter. Yesterday you could see Orion’s first stars pop up over the eastern horizon at 10 o’clock local time and glimpse the entire constellation about an hour later at 11 p.m. But because the U.S. switched back to standard time this morning (Nov. 3) Orion now rises an hour earlier around 9 p.m. and is fully visible, provided you have a reasonably good view of the eastern sky, by 10 p.m.

The first hint of Orion rising is the star Bellatrix, located in a line from the Pleiades through Aldebaran and down towards the eastern horizon. Bob King

What a joy it is to see Orion slowly climb out from the horizon haze. Dress in warm clothes and pull up a lawn chair. The first star in the figure to appear is Bellatrix in the hunter’s shoulder. Bellatrix is easy to spot because it’s directly in line with the Pleiades (Seven Sisters) and Hyades star clusters and shines at magnitude 1.6, a tad brighter than the stars of the Big Dipper.

Next up is the constellation’s Alpha Star, Betelgeuse, which follows about 20-25 minutes later. Watch for its fiery gleam not quite a fist to the lower left of Bellatrix. The time varies because the angle at which Orion rises — or any constellation for that matter — varies according to latitude. Five minutes after Betelgeuse, the westernmost star in Orion’s Belt, called Mintaka and derived from the Arabic “Al Mintakah,” the Belt. Within 15 minutes of Mintaka’s rising the entire belt is now visible standing nearly straight up and down at the horizon. To see all three stacked one atop the other in binoculars makes a beautiful sight.

By 10 p.m. in early November the main figure of Orion has risen into view in the east-southeastern sky. Stellarium

Mintaka’s cohorts include Alnilam and Alnitak, Arabic for “sapphire” and “the girdle,” respectively. As the Belt is rising, Rigel sputters into view. Notice how much it twinkles. This is caused due by increased atmospheric turbulence present across one’s line of sight when viewing bright stars at very low altitude. Rigel is Orion’s consistently brightest star at magnitude 0.1 — Betelgeuse is typically a bit fainter (around 0.5), but it’s light is variable, ranging from magnitude 0 at brightest to 1.3.

Orion the Hunter is a magnificent sight at rising and easily visible in less than pristine skies. Bob King

About 10-15 minutes after the Belt is up, use binoculars and place it off to the upper left side of the field of view, then scan down to the lower right side of the same view to find a fuzzy spot that looks like a tiny cloud with a star inside. That’s the Orion Nebula, a cloud of gas and dust 24 light years wide congealing into thousands of brand new stars 1,344 light years away.

Some 35 minutes after the Belt clears the mist, you’ll see the final bright star that completes Orion’s basic rectangular outline. Named Saiph and pronounced the same as the word “safe,” this second magnitude star is Arabic for “sword of the giant,” referring to one of two or three weapons Orion brandishes. The others are a club and a bow and arrow.

Watching stars rise not only reminds us we live on a spinning planet but also to slow down and enjoy nature at its own pace.

2 Responses

  1. Edward M Boll

    I wasn’t even looking for it but caught Venus last night. If I am right, it is 17 degrees from there to Jupiter, and 21 degrees farther to Saturn.

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