January 2020

Astronomy ... and You 2020
“Uncle Bob”

2020 overview

For January: Orion … and You

Orion …

Orion is very recognizable as a human figure in the winter skies. Although the head is relatively dim, the figure has prominent shoulders, feet, belt, and dagger (or sword). Almost all cultures regard “him” as a hunter or a warrior. Looking closer, we see dimmer stars appearing as a club held overhead, and as a shield protecting against Taurus the Bull to the west.

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From space.com - “With one exception, all of the main stars in Orion are bright young blue giants or supergiants, ranging in distance from Bellatrix (243 light-years) to Alnilam (1,359 light-years). The Orion Nebula is farther away than any of the [unaided eye] stars at a distance of about 1,600 light-years.

“The exception is the star Betelgeuse, which is a red giant and one of the largest stars known. It is also the only star in the sky large enough and close enough to have been imaged as a disk in the Hubble Space Telescope. Observers with a keen eye should be able to see the difference in color between Betelgeuse and all [sic] the other stars in Orion.”


The quote mentions the great Orion Nebula. This is a star-forming region located around the middle “star” of the sword; in fact, the four stars of the Trapezium [below] are all housed there. Even with unaided eye, viewers should be able to detect fuzziness. I have seen it fuzzy pink in certain atmospheric conditions. In any size telescope, the view is one of the most breath-taking sights in the entire night sky.

Credits: K.L. Luhman (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.); and G. Schneider, E. Young, G. Rieke, A. Cotera, H. Chen, M. Rieke, R. Thompson (Steward Observatory, University of Arizona, Tucson, Ariz.) and NASA/ESA

Don’t take my word for it. Burnham states, “To many others it creates, as does no other vista of the heavens, the single overpowering impression of primeval chaos.” More on this when below we play the game “Name that Neb,” an Uncle Bob original.

Now, as to the stars in Orion, there are really only two competitors for primacy, and oh, what a competition! Red supergiant Betelgeuse vs. blue supergiant Rigel. As an amateur tennis player, I see Betelgeuse as a sore right shoulder, and as a winter hiker, I see Rigel as a cold left foot, but let’s take their temperatures. Even though Rigel is the brighter star it earns the beta rank as compared with alpha Betelgeuse. Rigel is hot and blue and bright. How hot? Twelve thousand degrees Celsius. How bright? Fifty-seven thousand times brighter than our Sun.

Rigel’s rival is much nearer to us. Betelgeuse is an older star that is consuming fuels other than pure hydrogen and helium. Its surface temp is a “cool” 3000 degrees. It’s a gas giant in all respects. Even though it is over a hundred million times the volume, its density is estimated at one billionth that of the Sun.

Both Rigel, because of its fierceness, and Betelgeuse because of its size and age could be close to going supernova, i.e. blowing up; but Betelgeuse, being much closer than the rest of constellation Orion, could actually impact the environment in our own solar system, and it could be as soon as within a hundred thousand years. Rigel may be only 20,000 years behind that, but he is at a safer distance. The other bright stars of Orion are in Rigel’s camp – young, hot and blue.

… and You

1. Betelgeuse. Just how big is it? If it were our own sun would we be orbiting it at 93,000,000 miles away, or would we and other planets be subsumed by it? Find out here:


2. I’ve seen Rigel’s tiny blue companion through a scope. How can we tell if this is a binary system or just a near and far “visual double” aligned from our perspective? Binary stars often orbit one another. Do they all? What measurements can be taken to find out? Are there binary systems which don’t do the do-si-do? There are many areas in Orion that house more than two interacting stars. How rare are the double and multiple star systems?


3. I set out this constellation series intent upon covering what is accessible to readers with no access to big telescopes. Now, just two months in, I shatter that guideline. My excuse is that Orion, aside from the bright skeleton, is loaded with awesome nebulae aside from the one bearing its name. As a matter of fact, almost all of the constellation is enshrouded with gas and these nebulae are more apparent when near the bright stars. They are lit up.

I can justify this coverage by reminding readers that the internet makes these deep sky objects somewhat accessible to everyone. We will celebrate this visual feast by playing a game I'm calling …

Name That Neb

There are no wrong answers in this game. The aim is to have you imagine being the first person ever to have seen each of the following of Orion’s nebulae, and having the authority to name each one. I’ll put the official names on the results page.

1. credit:- Adam Block/Mount Lemmon Sky Center/University of Arizona
2. Credit: 2MASS Collaboration, U. Mass., IPAC
3. Credits: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team
4. credit:- ESO/Igor Chekalin
5. Credit: (Top) NASA, NOAO, ESA, Hubble Heritage Team (STScI / AURA)
(Bottom) T.A. Rector (NOAO/AURA/NSF), Hubble Heritage Team
6. credit:- NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

Nebula names and other information is on the solutions page.

Resource: Burnham's Celestial Handbook, vol. 2

Next month: Auriga, Charioteer or Shepherd?

January 2020

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