Post Archives: Twelve Great Stars for the Homeschool Year

For live links, click to: riverhouses.org/2019-arcturus

July is the middle month of Hercules Term in the River Houses, and as our monthly star calendar will tell you, July’s great star is Arcturus, the brightest star in the constellation Boötes the Herdsman. Its formal designation is α Boötis — “alpha of Boötes.” Boötes and Arcturus are already high overhead in the early evening this month, passing off to the west as the night goes on. With Regulus (our April star) and Spica (our June star), Arcturus forms “the Spring Triangle” (even though we’re now into summer).

If you want to introduce your students to Arcturus, you can start with some basic astronomy from your homeschool star atlas (riverhouses.org/books):

“Boötes is an easily recognized constellation resembling a huge kite. Arcturus, its brightest star, has a magnitude of –0.1 and is the 4th brightest star visible from Northern latitudes. Arcturus can be located by following backwards the curve of the Big Dipper handle; the curved line connecting these stars extended about 30º will lead your eye to Arcturus. It is a giant star about 80 times as bright as the sun and is 37 light years away.“ (Celestron Sky Maps, page 8)

The planisphere on the front of your star atlas will also help you locate Arcturus, and that’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Arcturus is packed with additional information on everything from astrometry to cultural history.

Arcturus is an ancient orange-yellow giant about seven billion years old. It has roughly the same mass as our sun, but it has expanded to enormous size as its supply of hydrogen has become depleted. It’s also relatively close to us — current estimates of its distance put it at about 37 light years. It’s generally thought to be a single star, without any companions.

The name Arcturus comes from the Greek and means “watcher of the bear” or “guardian of the bear” — a reference to its association with the constellation Ursa Major (the Great Bear, including the Big Dipper), which Boötes and Arcturus follow around the pole. Arcturus and the other stars of Boötes were well known to the Greeks, and as with any ancient celestial configuration they are surrounded by many different and sometimes contradictory mythological accounts of their origins.

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 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 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 — these are the dimmest objects 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 monthly “great star” 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. 🌟

For live links, click to: riverhouses.org/2019-spica 😊

June is the first month of Hercules Term in the River Houses, and as the River Houses Star Calendar will tell you, our great-star-of-the-month for June is Spica, the brightest star in the constellation Virgo. Its formal designation is α Virginis — “alpha of Virgo.” Spica (in Latin) is the ear of grain — the spike — in the left hand of the harvest maiden Proserpina (Persephone in Greek).

If you want to introduce your students to Spica, you can start with some basic astronomy from your homeschool star atlas (riverhouses.org/books):

“Virgo is both a zodiacal and equatorial constellation. Spica, its brightest star, is about 30º southwest of Arcturus in Boötes [next month’s great star] and forms the southernmost point of the Diamond of Virgo. Spica has a magnitude of 1.2 and it’s the 14th of the 20 brightest stars in the sky. The autumnal equinox, where the sun crosses the celestial equator on its journey south, is located close to the star η [eta] Virginis. In the rough square formed by Denebola in Leo [the lion’s tail] and ε [epsilon], γ [gamma] and β [beta] Virginis lies the so-called ‘Field of the Nebulae’ where Herschel discovered 323 nebulae; some of these are visible in a small telescope.“ (Celestron Sky Maps, page 7)

The planisphere on the front of your star atlas will help you locate Spica, and that’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Spica is packed with additional information on everything from astrometrics to cultural history.

Spica is a blue-white giant about seven times the diameter of the sun. It has a small companion that is invisible to the eye (even with a telescope) but that can be detected spectroscopically. The Spica pair is about 250 light years distant — close in astronomical terms — and it’s also quite young: about 12.5 million years old.

Spica is very close to the ecliptic, the line followed by the moon, sun, and planets as they cross the earth’s sky, and so on rare occasions it is briefly covered by them — an event called an occultation. The last occultation of Spica by Venus occurred in the year 1783, and the next will occur in 2197.

Measurements of Spica’s position are believed to have led the ancient astronomer Hipparchus to discover the precession of the equinoxes.

Spica has given its name to a World War II cargo ship, a teenage detective in a Japanese manga series, and (of course!) the South Korean pop group Spica:

This month, why not 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. ✨

❡ 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 monthly “great star” posts featuring twelve of the brightest 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. 🌟

For live links, click to: riverhouses.org/2019-polaris 😊

May is the last month of Leo Term in the River Houses, and as the monthly River Houses Star Calendar will tell you, our great-star-of-the-month for May is Polaris, the North Star or Pole Star in the constellation Ursa Minor, the Little Bear. Its formal designation is α Ursae Minoris — “alpha of Ursa Minor.”

Polaris is not an especially bright star — only magnitude 2 or so — and there’s nothing intrinsically special about it. Nevertheless, it’s one of the most important stars in the sky from our terrestrial human point of view because the earth’s orientation in space happens to put Polaris directly above our north pole. That means that as the earth rotates each day on its axis, all the other stars turn through the sky, but Polaris keeps its place: it’s a fixed point in the otherwise turning sky.

Which way is north? Look to Polaris. Want to know your latitude in the northern hemisphere? Your latitude corresponds to the angular elevation of Polaris above a level horizon. If you were at the equator, Polaris would be exactly at the horizon all night, and if you then walked your way to the north pole, Polaris would be at a higher and higher point each night until you reached the pole, when it would be 90º up from the horizon — straight overhead at the zenith.

Polaris is the alpha star — the brightest star — in the small constellation Ursa Minor, the Little Bear or Little Dipper. It’s the star at the end of the Little Dipper’s handle, and you can find it by locating the Big Dipper (Ursa Major), which is generally more conspicuous, and following the two “pointer” stars of the Big Dipper across the sky to Polaris.

The planisphere on the front of your star atlas (riverhouses.org/books) will help you locate Polaris, and that’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Polaris is packed with additional information on everything from astrometrics to cultural history.

The Polaris we see as a single star is in fact a triple star system. The primary star of the system — the source of nearly all the light that comes to us — is a yellow supergiant more than 30 times the diameter of the sun. It has a tiny close companion that can only be detected in powerful telescopes, and a more distant companion that can be fairly easily resolved by amateur observers. The Polaris system is about 400 light years distant — the light we see when we look at Polaris was actually emitted by the star about 400 years ago.

“I am as constant as the northern star,” says Shakespeare’s Julius Caesar. This month, take your homeschool students out at dusk and introduce them to this great fixed star, 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.

❡ 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 monthly “great star” posts featuring twelve of the brightest 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. 🌟

We’re going to start a new thing today: a monthly great star. March is the perfect month to begin this new tradition, because just as it’s getting dark each evening at this time of year the brightest star in earth’s night sky, Sirius, appears high in the south. Brilliant white Sirius will be our star for the month.

Sirius is the brightest star — the “alpha” star — in the constellation Canis Major, the Big Dog that trails behind Orion the Hunter as he crosses the winter and early spring sky to the west. Sirius is commonly called “the Dog Star,” marking as it does the Big Dog’s head. Its formal designation is α Canis Majoris — “alpha of Canis Major.”

If you want to introduce your students to Sirius, you can start with some basic astronomy from our recommended homeschool star atlas (riverhouses.org/books):

“Sirius, the brightest star in the sky (magnitude –1.44) is the most conspicuous star in this constellation [Canis Major, the Big Dog]. It is easily located by following downward the line connecting the three stars in the Belt of Orion. Sirius is the nearest star to the sun visible to the naked eye in the northern latitudes, being but 9 light years distant. It has a white dwarf companion, a star so dense that one cubic inch weighs a ton.“ (Celestron Sky Maps, page 18)

The planisphere on the front of your star atlas will help you locate Sirius, and that’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Sirius is packed with additional information on everything from astrometrics to cultural history.

Sirius is indeed a double star system, but the smaller star of the pair is only visible in the largest telescopes. The name Sirius means burning, shining, or scorching in Greek (σείριος), either from its brightness or from the timing of its dawn rising along with the sun in mid-summer. (Today, we tend to make seasonal associations with the stars and constellations according to their evening visibility, but in ancient times, it was the dates on which particular stars rose just ahead of the sun at dawn that was commonly used for calendrical purposes.)

Sirius is roughly twice the diameter of our sun, and it is much younger — less than 250 million years old, in contrast to the sun’s 4.6 billion year age. Sirius was one of the first stars whose “proper motion” against the distant background was confirmed. The astronomer Edmund Halley (1656–1742), by comparing contemporary measurements of the position of Sirius with those of the ancient astronomer Claudius Ptolemy (ca. 100–170), determined that Sirius had moved about 30 arc minutes across the sky since Ptolemy’s day — a positional change in 1500 years equivalent to the diameter of the moon. The “fixed stars” were not so fixed after all.

Just yesterday, as I was walking back from the grocery store around sunset, I turned to the south and there was Sirius emerging in the twilight, the first star of the evening. 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 easy to locate on a dark night.

❡ 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. Why not find a dark-sky spot near you this month and spend some quality homeschool time beneath the starry vault. 🌠 🔭 🌌 🌟