For live links, click to: riverhouses.org/2019-regulus 😊
We started a new tradition last month — a monthly great star — and this month we’re continuing and extending it. Please visit our homeschool calendars page and print a copy of our brand new River Houses Star Calendar, a simple one-page introduction to twelve of the great stars of the northern-hemisphere night sky that we will be learning about over the course of the year, and that we hope will become your friends for life:
April is the middle month of Leo Term, and as the new calendar will show you, our great-star-of-the-month for April is Regulus, the brightest star in constellation Leo, the Lion of the Heavens. Its formal designation is α Leonis — “alpha of Leo.” Leo and Regulus are high in the southern sky in the early evening this month, passing over to the west as the night goes on.
If you want to introduce your students to Regulus, you can start with some basic astronomy from your homeschool star atlas (riverhouses.org/books):
“Leo is a zodiacal constellation lying south of Ursa Major [the Great Bear, which includes the Big Dipper]. It is one of the most beautiful of the constellations and is easily recognized; the stars forming the head of the lion are arranged in the shape of a sickle, or reversed ‘?’. Regulus, its brightest star, has a magnitude of 1.3 and is 19th among the 20 brightest stars in the sky. It lies almost exactly on the plane of the ecliptic and is therefore eclipsed by the sun once a year (on about August 23).“ (Celestron Sky Maps, page 6)
The planisphere on the front of your star atlas will help you locate Regulus, and that’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Regulus is packed with additional information on everything from astrometrics to cultural history.
The Regulus we see is blue-white, but that Regulus is actually just the primary star (Regulus A) of a quadruple system that is arranged into two pairs: Regulus A and a suspected white dwarf that is detectable only spectroscopically, and Regulus B and C (a pair that is visible as a single star in small telescopes). The B-C pair orbit each other, and together they orbit the primary star Regulus A (and its own tiny companion).
The primary star Regulus A is about three times the diameter of our sun and it is spinning so fast that it bulges out at the equator: it takes only 16 hours to complete one rotation, in contrast to about 25 days for the sun. The four-star Regulus system is estimated to be about one billion years old — quite old, but less than a quarter of the age of our own solar system. If you’d like to give Regulus an in-person inspection just bring your earth-based spaceship up to the speed of light and you’ll be able to get there in only 79 years. 🚀
Download and print your own copy of our new River Houses Star Calendar (riverhouses.org/calendars) and follow along with us as we visit a different great star each month. 🌟
What stellar observations have you made in your homeschool lately? 😊
❡ 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. 🌠 🔭 🌌 🌟
❡ 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.