For live links, click to: riverhouses.org/2019-vega
August is the last month of Hercules Term in the River Houses, and as our monthly star calendar will tell you, August’s Great Star is Vega, the brightest star in the constellation Lyra the Lyre. Its formal designation is α Lyrae — “alpha of Lyra.” Vega is one of my favorites and it’s almost directly overhead (near the zenith) every evening this month just after sunset, passing off to the west as the night goes on.
If you want to introduce your students to Vega and Lyra, you can start with some basic astronomy from your homeschool star atlas (riverhouses.org/books):
“Lyra is easily identified because of Vega, a brilliant white star of magnitude 0.0, the fourth brightest star in the sky and the second brightest visible from northern latitudes. Four smaller stars lie in a faint but conspicuous parallelogram just to the southeast of Vega. Although a small constellation, Lyra is rich in stars; sweep slowly with binoculars, particularly the area between β [beta] and γ [gamma] Lyrae. Do not fail to observe β [beta] Lyrae, an eclipsing binary whose light changes are visible to the naked eye, the magnitude varying from 3.4 to 4.3. ε [epsilon] Lyrae is the famous “double double”; persons with very keen eyesight can see the two components. They are easily split with binoculars. In a telescope, each of the components itself becomes a double.“ (Celestron Sky Maps, page 12)
The planisphere on the front of your star atlas will help you locate Vega, and that’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Vega is packed with additional information on everything from astrometry to cultural history.
Because of its prominence in the northern hemisphere night sky, Vega has played an important role in the development of modern astronomy. It was the first star other than the sun to be photographed (by daguerreotype in 1850), and the first star other than the sun to have its spectrum analyzed (in the 1870s). When the scale of stellar magnitudes was refined during the nineteenth century, Vega was chosen as the principal reference star with a defined magnitude of 0.0.
Modern calculations put Vega at a distance of about 25 light years — practically next door in astronomical terms. It’s estimated to be about two and a half times the diameter of the sun, but it is rotating so rapidly that it bulges out at the equator, making it more egg-shaped than spherical. It’s also quite a bit younger than the sun, with an estimated age of only 455 million years (compared to the sun’s age of more than 4.5 billion).
This month, take your homeschool students out at dusk and introduce them to this great nearby sun, and teach them its name, and so give them a new friend for life.
What stellar observations have you made in your homeschool lately? 😊
❡ Alpha and beta and gamma, oh my: Most of the principal stars within each constellation have both old vernacular names — Vega, Sirius, Arcturus, and so on — as well as more formal scientific designations. The German astronomer Johann Bayer (1572–1625) devised the formal system of star designations that is still in common use today. In Bayer’s system, the stars in each constellation, from brightest to dimmest, are assigned a lowercase letter of the Greek alphabet: α (alpha, brightest), β (beta, second brightest), γ (gamma, third brightest), δ (delta, fourth brightest), and so on. This letter designation is combined with the Latin name of the constellation in its possessive (genitive) form: Lyra becomes Lyrae (“of Lyra”), Canis Major becomes Canis Majoris (“of Canis Major”), and so on. The brightest star in the constellation Lyra (the star Vega) thus becomes α Lyrae (“alpha of Lyra”), the brightest star in Canis Major (the star Sirius) becomes α Canis Majoris (“alpha of Canis Major”), and so on, through all 24 Greek letters and all 88 constellations. How bright would you expect, say, the σ (sigma) star of Orion to be? Not very bright — it’s far down the alphabet — but σ Orionis happens to be the top star of Orion’s sword, so even though it’s not very bright it’s still notable and easy to locate on a dark night. ✨
❡ Star bright: The brightness of a star as we see it in our night sky is its magnitude — or more properly speaking, its apparent magnitude. The scale of star magnitudes was developed centuries ago, long before modern measuring instruments were invented, so it can be a little bit confusing for beginners. Originally, the brightest stars in the sky were called “first magnitude” and the less-bright stars “second magnitude,” “third magnitude,” and so on, down to the dimmest stars visible to the naked eye, which were called “sixth magnitude.” In the nineteenth century the star Vega (our August star) was chosen as the standard brightness reference and its value on the magnitude scale was defined to be zero (0.0). Five steps in magnitude (from 0.0 to 5.0 or from 1.0 to 6.0) was defined to be a change in brightness of 100 times: a star 100 times dimmer than Vega (0.0) was defined to be a magnitude 5.0 star. Vega is not quite the brightest star is the sky, however, so the scale also had to be extended into negative numbers: Sirius, for example, is magnitude –1.5, about three times brighter than Vega (at 0.0). The planet Venus at its brightest is about magnitude –4.2; the full moon is about magnitude –12.9; the sun is magnitude –26.7. By contrast, the dimmest stars visible to the naked eye in a populated, light-polluted area are about magnitude 3.0; the dimmest stars visible under very dark conditions are about magnitude 6.5. The Hubble Space Telescope has imaged distant stars and galaxies below magnitude 30, the dimmest celestial objects humans have seen so far. 🔭
❡ Watchers of the skies: Teaching your students to recognize the constellations is one of the simplest and most enduring gifts you can give them. The planisphere on the front of your River Houses star atlas (riverhouses.org/books) will let you dial up the northern hemisphere sky for any night of the year, and the descriptions and maps of each constellation will point out the highlights, including the names and characteristics of the brightest stars. Your general world atlas also has beautiful maps of the whole northern and southern hemisphere night skies on plates 121–122. Why not find a dark-sky spot near you this month and spend some quality homeschool time beneath the starry vault. 🌠 🔭 🌌 🌟
❡ First star I see tonight: This is one of our regular Homeschool Astronomy posts featuring twelve of the most notable stars of the northern hemisphere night sky. Download and print your own copy of our River Houses Star Calendar (riverhouses.org/calendars) and follow along with us as we visit a different Great Star each month — and make each one of them a homeschool friend for life. 🌟