Seeking bright G-class stars for public astronomy program

[Anthony Barreiro]

Greetings Asteroidals. On March 22 (evening) and 23 (midday) I'll be helping with a public astronomy program at Hayward Regional Shoreline. The theme of the program is "getting to know our neighborhood star." The Saturday afternoon program will include viewing the Sun through telescopes with white and hydrogen alpha filters.

For the Friday evening program I think it might be fun to look at some nearby G-class stars through a telescope, to get an idea of what our star would look like from light years away. (The shoreline is in a moderately light-polluted urban environment, and we'll have a waxing gibbous Moon, so conditions won't allow looking for any faint stars.) The only G-class stars that come immediately to mind for me are Alpha Centauri (too far south) and 61 Cygni (too far east). And I can't figure out how to search my planetarium software (sky safari 3 pro) for G-class stars, 10th magnitude or brighter, between right ascension 2 hours and 12 hours, and north of -10 degrees declination; or between RA 0 hours and 14 hours and north of +30 degrees.

If you're able to make any suggestions I would be most grateful.

[neufer]

On March 22 (evening) and 23 (midday) I'll be helping with a public astronomy program at Hayward Regional Shoreline. The theme of the program is "getting to know our neighborhood star." The Saturday afternoon program will include viewing the Sun through telescopes with white and hydrogen alpha filters.

For the Friday evening program I think it might be fun to look at some nearby G-class stars through a telescope, to get an idea of what our star would look like from light years away. (The shoreline is in a moderately light-polluted urban environment, and we'll have a waxing gibbous Moon, so conditions won't allow looking for any faint stars.) The only G-class stars that come immediately to mind for me are Alpha Centauri (too far south) and 61 Cygni (too far east). And I can't figure out how to search my planetarium software (sky safari 3 pro) for G-class stars, 10th magnitude or brighter, between right ascension 2 hours and 12 hours, and north of -10 degrees declination; or between RA 0 hours and 14 hours and north of +30 degrees.

If you're able to make any suggestions I would be most grateful.

The ideal candidate would be Tau Ceti.

Unfortunately, on March 22, Tau Ceti will be setting with the Sun.

You could always settle for:

• Procyon: a white main-sequence star of spectral type F5 IV–V,
  Capella: two bright unresolved, large type-G giant stars,
  Pollux: a giant star with a stellar classification of K0 III.

[rstevenson]

Chi1 Ori is a G0 star, up at the tip of Orion's raised arm. Absolute magnitude is 4.40; not sure what apparent magnitude is.

Rob

[neufer]

Chi1 Ori is a G0 star, up at the tip of Orion's raised arm.
Absolute magnitude is 4.40; not sure what apparent magnitude is.

At the tip of Orion's raised club:

• Absolute magnitude (MV) 4.67
  Apparent magnitude (V) 4.39

http://stars.astro.illinois.edu/sow/chi1ori.html
http://www.solstation.com/stars/chi1ori2.htm

[Anthony Barreiro]

The ideal candidate would be Tau Ceti.

Unfortunately, on March 22, Tau Ceti will be setting with the Sun.

(You could always settle for Pollux: a giant star with a stellar classification of K0 III)

Chi1 Ori is a G0 star, up at the tip of Orion's raised arm. Absolute magnitude is 4.40; not sure what apparent magnitude is.

Rob

Thanks Rob. Chi-1 Orionis will be my target. It's fourth magnitude, well placed in the evening during March, and in the same finder field as Zeta Tauri. It's pretty close at 28 light years. And as a bonus, it shows that most stars are doubles.

Neufer, thanks for suggesting Tau Ceti, I'll remember that star for late fall and winter programs. Too bad this is the wrong time of year to see that particular star. And thanks for the links to additional info on Chi-1 Ori.

Pollux wouldn't work for this program. I need a main-sequence G-class star to show that from a distance our Sun would be very dim. The audience won't have any prior knowledge of astronomy, so I'm not going to try to teach them the Hertzsprung-Russell diagram and stellar evolution. My goal is to teach them big-hot-bright vs. small-cool-dim. (Almost everything I teach in my public programs, starting with "the North Star is always in the same place in the sky" is an unacknowledged approximation.)

You guys rock.

[Ann]

Check out this page. Professor emeritus Jim Kaler lists stars according to their spectral classes. You can click on any star to find information about it.

Here you can see that Chi-1 Orionis is indeed a great choice for a main sequence nearby G-type star. There is also Iota Persei, for example. A star that is a little cooler and fainter than the Sun, but still a nearby main sequence G-type star, is spectral class G5V Kappa-1 Ceti. Intriguingly, there is another G5 star right next to Kappa-1 Ceti, namely Kappa-2 Ceti. This star, however, is a giant, ten times farther away than Kappa-1 and 43 times brighter than the Sun. If you want to, you might check out Menkar, Alpha Ceti, an M-class giant more than 400 times brighter than the Sun, while you're at it.

Ann

[Ann]

Okay, Anthony, I've got it! I really think you should show your students Eta Cassiopeiae, a somewhat famous double star where the primary is a G0V main sequence star similar to the Sun, and the companion, which should show up moderately well in your telescope, is of spectral class K7V! The companion has 57% of the Sun's mass, but only 6% of its luminosity! It is noticeably more orange than its G-type primary, too.

A good thing about demonstrating Eta Cas is that you can bring home an important lesson about the stars in the sky: although 99% of the stars you can see with your naked eye are intrinsically brighter than the Sun, about 95% of all stars in the Milky Way are believed to be fainter than the Sun! That's because the Sun is "average" in that its luminosity is about midway between the brightest and the faintest stars, but it is "not average" due to the fact that by far most stars are small and dim.

Read about Eta Cas here and here.

Ann

[Anthony Barreiro]

Ann, thank you so much. I've added iota persei and eta cas to my list of nearby main-sequence G-class stars that will be visible in the early evening this month. Chi-1 orionis will have the advantage of being near the zenith, while Perseus and especially Cassiopeia are getting low in the northwest. But it's great to have more options and examples. Professor Kaler's list of stars by spectral class is a great resource.

One of the things I hope to get across is that almost all of the stars we see in the sky are brighter than our Sun, but the Sun is brighter than most of the stars in our galaxy. I love watching people's faces as their understanding of the cosmos expands.

[Anthony Barreiro]

Thanks everyone for your suggestions and information. During twilight we saw Comet PanSTARRS through mounted 15x70 binoculars, then we had a talk about what makes stars shine, space weather, etc. We had good enough weather to see Eta Cas, Iota Persei, and Chi-1 Orionis, and they were all appropriately underwhelming. Eta Cas was the star of this part of the show, being a double star with pretty colors. After we were done with our G-Class cousins we looked at the Orion nebula to suggest our Sun's baby pictures, and the Pleiades as a high school year book. Folks really enjoyed these objects, especially the Pleiades through the binoculars. Then we looked at the Moon and Jupiter, mostly because they're pretty, but also because they reflect sunlight.

All in all it was an interesting and enjoyable evening. And we had good weather for looking at the Sun Saturday, as well. There were only a couple of sunspots, both near the limb and not easy to see, but some very nice prominences and filaments in Hydrogen-alpha light. For a while there were high cirrus clouds and we saw a bright solar halo, a chance to talk about atmospheric refraction.

[Ann]

Sounds great, Anthony! I wish I could have been there!

Ann