🌟 Post Archives: Twelve Great Stars for the Homeschool Year

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

November is the third month of Cygnus Term in the River Houses, and as our monthly star calendar will show you, November’s Great Star is Algol, “the Demon Star,” the second-brightest star in the constellation Perseus the Hero. Its formal designation is β Persei — “beta of Perseus.” Perseus and Algol are high in the east in the evening now, passing right overhead about midnight.

If you want to introduce your students to Algol and Perseus, you can start with some basic astronomy and astronomical mythology from your backyard star guide (riverhouses.org/books):

“Visible for much of the year in the northern sky, Perseus straddles the Milky Way between Cassiopeia and Andromeda, characters from the same Greek myth in which he takes center stage as the story’s hero. This constellation is relatively easy to pick out for a beginning stargazer. Although visible for much of the year, the best times to view Perseus are in the late fall months.

“With magnitude 1.8 Mirfak at its center, and five other stars of magnitude 3 or greater, Perseus contains bright and notable signposts. Among them is Algol (Beta Persei), a well-known eclipsing variable that dims by a full magnitude for about 10 hours every three days….

“[The mythological Perseus,] the half-mortal son of Zeus, is one of the more prominent Greco-Roman heroes. A favorite of Athena, he received many gifts from her, including a polished shield. In going into battle with the Gorgon Medusa — who, with one look, could turn any human or animal into stone — Perseus used the shield as a mirror to avoid her direct gaze. When he lopped off her head, the winged horse Pegasus was born of her blood and Perseus took it for his own. In his second great feat, Perseus used Medusa’s head as a weapon to help him rescue Andromeda from the sea monster Cetus: even severed from her body, the Gorgon’s stare turned Cetus to stone.“ (Backyard Guide to the Night Sky, pages 244–245)

That’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Algol is packed with additional information on everything from astrometry to cultural history.

The Algol we see is actually a complex three-star system (Algol A, B, and C). Algol A and B orbit each other at just the right angle from our perspective on earth such that they pass in front of each other every few days, causing the apparent brightness of “Algol” to vary. The Algol A–B pair is thus referred to as an eclipsing binary: when you see it dim, you are watching the actual crossing of these two orbiting stars 93 light years away (practically next door in astronomical terms).

The name Algol comes from the Arabic al-ghūl meaning “the ghoul” or “the demon,” and from this we get Algol’s colloquial name “the Demon Star” — the demon in question being Medusa the Gorgon whose decapitated head, marked by Algol, is being carried by Perseus.

Sometime this month, take your homeschool students out at dusk and introduce them to this great system of suns, 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 mark the top 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, its apparent magnitude. The scale of star magnitudes was developed 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 (our March star), 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 in orbit around the earth has photographed distant stars and galaxies below magnitude 30, the dimmest celestial objects humans have seen so far. 🔭

❡ And all dishevelled wandering stars: How far away are the stars? Do they all occupy a single celestial “dome” that rotates through the heavens (as some ancient and medieval astronomers believed), or are they scattered through space at different individual distances? Astronomers had long suspected that the fixed stars existed at different distances from us, but early attempts to measure those distances failed. It was not until the early 1800s that instruments and measuring techniques became precise enough to allow the first stellar distances to be calculated using the technique of parallax. Parallax is the displacement in the apparent position of an object with respect to the background when an observer moves from side to side. It’s an ordinary phenomenon you experience every day — it’s how we judge distances as we move through the landscape. Stellar parallaxes are extremely small — fractions of an arc-second (one 3600th of a degree) — and they are calculated by measuring a star’s position against the background at opposite sides of the earth’s orbit, six months apart. (That’s the astronomical equivalent of taking one step to the side.) Vega, our August star, was one of the first stars to have its parallax measured; modern estimates put it at about 0.13 arc-seconds. Apply some trigonometry, and that yields a distance of about 25 light years. 🔭

❡ Watchers of the skies: Teaching your students to recognize the constellations is one of the simplest and most enduring gifts you can give them. We recommend the handy Backyard Guide to the Night Sky (riverhouses.org/books) as a general family reference — it will help you identify all the northern hemisphere constellations and will point out many highlights, including the names and characteristics of the brightest stars. Your recommended 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-alpheratz

October is the middle month of Cygnus Term in the River Houses, and as our monthly star calendar will show you, October’s Great Star is blue-white Alpheratz, the brightest star in the constellation Andromeda, the chained maiden of Greek mythology who was rescued by the hero Perseus. Its formal designation is α Andromedae — “alpha of Andromeda.” Andromeda and Alpheratz are high in the east at sunset now, passing directly overhead around midnight and then off to the west as the night goes on.

Although Alpheratz is officially part of Andromeda, it lies on the border of the adjacent constellation Pegasus and can be most easily recognized as the top left star (when you’re facing south) of the asterism called the Great Square of Pegasus. Its name derives from an Arabic phrase meaning “the navel of the horse,” reflecting its position in adjacent Pegasus.

If you want to introduce your students to Alpheratz and Andromeda, you can start with some basic astronomical mythology from your backyard star guide (riverhouses.org/books):

“In ancient Greek myth, Princess Andromeda of Ethiopia was chained to a rock as a sacrifice to the gods. In the sky, Andromeda is a faint V-shaped constellation that is most often seen upside down. To locate her on fall evenings, trace a line northeast from [the 2.1-magnitude star Alpheratz,] the northeast corner of the Great Square of Pegasus….

“Andromeda’s mother, Cassiopeia, claimed that her daughter’s beauty surpassed that of the daughters of Nereus, a god of the sea and father-in-law of Poseidon. Angered by her boasting, Poseidon sent the monster Cetus to destroy the kingdom of Ethiopia unless Cassiopeia and her husband Cepheus sacrificed their daughter. The princess was rescued by Perseus, who used the head of Medusa to turn Cetus to stone. The whole cast of the tale — her father Cepheus, Cassiopeia, Cetus, Perseus, and the hero’s winged horse Pegasus — are all nearby in the sky.“ (Backyard Guide to the Night Sky, pages 248–249)

That’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Alpheratz is packed with additional information on everything from astrometry to cultural history.

The blue-white star we see as Alpheratz is actually a close double star — two suns orbiting each other — but they are so close that they cannot be resolved even with a sizeable telescope. The double nature of Alpheratz was first detected by close examination of the way the star’s light spectrum changes from week to week. These spectroscopic measurements suggest the two Alpheratz companions circle each other once every 97 days. (Compare this to the earth’s orbit around the sun, which takes 365 days.)

The Alpheratz system is fairly close to us in astronomical terms: a little less than 100 light years away. (The light you see from it tonight was emitted in the early twentieth century and has been traveling toward us for nearly a hundred years until the moment it strikes your eye.) The larger of the two Alpheratz companion stars is almost three times the diameter of the sun, and it’s quite young: only about 60 million years old, in contrast to more than 4.5 billion for our old yellow sun.

Sometime this month, take your homeschool students out at dusk and introduce them to this great nearby 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 mark the top 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 (our March star), 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 photographed distant stars and galaxies below magnitude 30, the dimmest celestial objects humans have seen so far. 🔭

❡ And all dishevelled wandering stars: How far away are the stars? Do they all occupy a single celestial “dome” that rotates through the heavens (as some ancient and medieval astronomers believed), or are they scattered through space at different individual distances? Astronomers had long suspected that the fixed stars existed at different distances from us, but early attempts to measure those distances failed. It was not until the early 1800s that instruments and measuring techniques became precise enough to allow the first stellar distances to be calculated using the technique of parallax. Parallax is the displacement in the apparent position of an object with respect to the background when an observer moves from side to side. It’s an ordinary phenomenon you experience every day — it’s how we judge distances as we move through the landscape. Stellar parallaxes are extremely small — fractions of an arc-second (one 3600th of a degree) — and they are calculated by measuring a star’s position against the background at opposite sides of the earth’s orbit, six months apart. (That’s the astronomical equivalent of taking one step to the side.) Vega, our August star, was one of the first stars to have its parallax measured; modern estimates put it at about 0.13 arc-seconds. Apply some trigonometry, and that yields a distance of about 25 light years. 🔭

❡ Watchers of the skies: Teaching your students to recognize the constellations is one of the simplest and most enduring gifts you can give them. We recommend the handy Backyard Guide to the Night Sky (riverhouses.org/books) as a general family reference — it will help you identify all the northern hemisphere constellations and will point out many highlights, including the names and characteristics of the brightest stars. Your recommended 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-deneb

(This is the first of our monthly “Star Bright” posts for the 2019–2020 homeschool year. Print your own River Houses Star Calendar and follow along with us, and add your name to our free weekly mailing list to get great homeschool teaching ideas delivered right to your mailbox all through the year.)

September is the first month of Cygnus Term in the River Houses, and as our monthly star calendar will show you, September’s Great Star is Deneb, the brightest star in the constellation Cygnus the Swan. Its formal designation is α Cygni — “alpha of Cygnus.” Cygnus and Deneb are high in the east at dusk now, passing overhead in the early evening and flying to the west as the night goes on.

If you want to introduce your students to Deneb and Cygnus, you can start with some basic astronomy from your backyard star guide (riverhouses.org/books):

“Cygnus lies in what for observers is a dense and fascinating part of the sky. The bird’s wings span the Milky Way at a location packed with stars and an assortment of deep-sky objects. Owing to the positions of its bright stars it is sometimes called the Northern Cross — the northern parallel to the brilliant Southern Cross constellation in the Southern Hemisphere. You will see Cygnus highest in the sky in late summer and early fall, with its head pointing south like a bird on its migratory path toward warmer climates.

“Deneb, the alpha star and tail of the bird, is a brilliant magnitude-1 star that joins Altair and Vega to form the Summer Triangle. Deneb is 25 times more massive than our sun and 60,000 times more luminous.“ (Backyard Guide to the Night Sky, page 216)

That’s plenty for beginning students — your little lesson is done. If you want to get more advanced, the Wikipedia page on Deneb is packed with additional information on everything from astrometry to cultural history.

Deneb is an enormous blue-white supergiant, about 200 times the diameter of our sun. If it were placed at the center of our solar system it would extend out to engulf the orbits of Mercury, Venus, and the Earth. Deneb is estimated to be about 2,600 light years away, so the photons striking your eye when you gaze upon it were actually emitted by the star 2,600 years ago — when the ancient Greek poet Sappho was composing her lyrics in the eastern Aegean — and they have been traveling at the speed of light to greet us ever since. The name Deneb is Arabic for tail — it’s the tail of the swan for us, but for medieval Arabic astronomers it was usually imagined as the tail of a heavenly hen.

Some time during this first month of Cygnus Term, take your homeschool students out at dusk and introduce them to this giant 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 mark the top 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. We recommend the handy Backyard Guide to the Night Sky (riverhouses.org/books) as a general family reference — it will help you identify all the northern hemisphere constellations and will point out many highlights, including the names and characteristics of the brightest stars. Your recommended 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-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 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-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. 🌠 🔭 🌌 🌟