This section contains specific tips for teaching the project – facts you can tell your students as they work, and advice for solving common problems students may encounter.
Start by checking student knowledge on constellations. Most will have heard of a few famous constellations, like Orion or the Big Dipper. Strictly speaking, the Big Dipper is not a constellation – it’s an asterism, a pattern of stars that is part of a constellation. The Big Dipper is part of Ursa Major, the big bear. The handle of the dipper is the bear’s tail. In England, the Big Dipper is sometimes called the plough (plow).
The constellation shown on the front page of the project is Scorpius the scorpion. You can refer to it again when you tell the story of Orion – Scorpius chases Orion across the sky as the Earth rotates. In Hawaii, Scorpius’s long tail is known as “Maui’s Fishhook.” The demigod Maui pulled the Hawaiian Islands up from the sea with this hook. The brightest star in Scorpius is Antares, one of the reddest stars in the sky. In Greek mythology, it was the rival of Mars (Greek “Ares”), since it was just as red as Mars.
Be sure students understand that the Dove/Horse Constellation doesn’t represent any real star pattern. It’s just a simple picture to help them understand what constellations are. The idea of two-pictures-in-one is a common device used in perceptual psychology. You have probably seen other examples, such as the young girl/old woman illusion. As mentioned in the Procedure, this activity can provide a small moral lesson – hopefully students will argue passionately for a dove or horse, then realize that both sides were right. Ask students if they can think of other times when they have argued with their friends, only to realize that both sides were looking at the same facts from different perspectives. Some students may not be able to see the other dove/horse perspective at all.
Orion is one of the most famous constellations in the Northern Hemisphere. (If you’re doing this project in the Southern Hemisphere, students may not know what Orion looks like. Use a different constellation, like Crux [the Southern Cross], instead.) Orion is only visible in the fall and winter, because in the spring and summer it would appear during the day (and so it is drowned out by the Sun). Point out Orion’s shoulders, knees, and belt as you describe them. Orion also has a sword hanging down below his belt, and a bow extending to the right of his right shoulder. The Wikipedia Orion Constellation page includes several Greco-Roman-based legends about Orion that you can read to your students. Note that Scorpius always follows Orion around the sky as the Earth rotates. This was probably the inspiration for the legend that Orion was killed by a scorpion.
Stars in Orion
Students should know that magnitude measures how bright a star is, but they do not need to know the details of how magnitude works. Magnitude is a logarithmic scale, like the Richter scale for earthquakes or the decibel scale for volume. The magnitude scale is complicated because of its long and confusing history. The important thing for students to remember is that the scale is backward (brighter stars have smaller values), and that the scale is logarithmic, so small changes in magnitude mean big changes in brightness. Also remind students that magnitude means apparent brightness. A very bright star, very far away, might still look just as bright as a faint nearby star. Students should be able to see that effect in the table of stars in Orion.
A light-year is the distance light travels in a year. Scientists know the speed of light to a very high precision, so the distance light travels in a specific time makes a convenient measure of distance. A light-year is the most common unit of distance for stars and galaxies. The nearest star is about four light-years away. The lesson from the table of Orion stars is that, even though the stars appear similar, they have different properties and are at very different distances from Earth. Note that Rigel is farther away from Earth than Betelgeuse, but Rigel appears brighter. For this to be true, Rigel must be intrinsically brighter than Betelgeuse.
The most famous object in Orion is the Orion Nebula (M42). The middle “star” of Orion’s sword (below his belt) is not a star at all, but the nebula. Nebulae are places where new stars are born. The Orion Nebula is the brightest nebula in the night sky, and also the easiest to find. Encourage students to look for the nebula with their parents.
Other Shapes in Orion
Ask students what they can see in the Orion photo. Some students may have difficulty seeing anything other than a hunter. This should show how strongly what people know influences what they see. You might want to survey students to find out what shapes they can and cannot see in Orion.
Other than Orion and the Big Dipper, the most famous constellations are the 12 signs of the Zodiac, which most students should be familiar with. You might use this as an opportunity to discuss how science differs from astrology. In addition to the zodiac signs, the ancient Greeks identified several other constellations, such as Corona the Crown. Corona appears in the summer in the Northern Hemisphere. It’s a fairly easy constellation to find – it looks like a semicircle or C.
When Europeans started exploring the Southern Hemisphere, they faced a new sky, full of stars they could not see from the Northern Hemisphere. No one formed the stars of the southern sky into constellations until the mid-18th century. In 1750, French monk and astronomer Abbé Nicolas Louis de Lacaille (biography) set up an observatory at the Cape of Good Hope, at the southern tip of Africa. Over the next four years, he found more than 10,000 stars with his half-inch telescope. He organized many of the stars into 14 new constellations, all of which he named after recent scientific inventions. Some of his constellations include Telescopium the Telescope, Fornax the Furnace, and Antila the Air Pump. All the new constellations are rather small and ordinary-looking. Ask students what they think Microscopium looks like.
If students are interested in the other constellations, they can read about the 88 constellations at The Constellations Table web site. Astronomers use names of constellations to refer to stars and other objects. The stars are named with Greek letters, from alpha to omega in order of decreasing brightness, followed by the “generative form” of the constellation. For example, Regulus, the brightest star in the constellation Leo, is known as “Alpha Leonis.” The Constellations and their Stars gives the generative form of each constellation; see the alphabetical list and click on a constellation name.
Constellations in SkyServer
To find their constellations, students should draw a simple shape on the grid. In the test class, several students drew butterflies. Be sure that students mark their “stars” clearly at grid points on the grid (or graph paper). Tell students to look through SkyServer to find star patterns that look like their constellation.
Students should be able to find their constellations just by panning and zooming. You might want to have some or all students enter a new location (RA/Dec) and click “Get Image,” so that not all students are looking at the same part of the sky. RA (“right ascension”) is longitude in the sky; dec (“declination”) is latitude in the sky. Dec = 90 degrees is what you see when you look directly up at the North Pole (the North Star is at about Dec = 90). Dec = -90 degrees is what you see when you look directly up at the South Pole. RA runs from 0 to 360 (no + or -) around the sky. The Earth rotates through 15 degrees of RA each hour. The “Prime Meridian” of RA, RA = 0, is the spot where the Sun crosses Dec = 0 during the Spring Equinox.
If you get a message that says, “requested (ra,dec) is outside the SDSS footprint,” you have picked a location where the SDSS does not have data. Enter another location and click “Get Image” again.
The five magnitudes u,g,r,i,z are magnitudes in five colors of light: ultraviolet, red, green, and two infrared wavelengths i and z. The g magnitude is closest to what your eyes would see. Most stars on SkyServer have magnitudes between about 10 and 20, between 100 and 1,000,000 times fainter than the faintest thing you can see with your naked eye.
When students find their constellations, you should have them point them out to you. Remind them that it’s OK to have galaxies in their constellations. (There are no galaxies that connect the dots in the 88 constellations because all galaxies look very faint to the naked eye.)
Students should click on each star or galaxy in the constellation, one after the other. Then, they should click “Add to Notes.” A small red check will appear next to “Add to Notes.” After students have added each star or galaxy, they should click “Show Notes.” The notebook will look like this:
Click “Export” to save the notebook to your computer. It will save as HTML. If you want to contribute some students’ work to SkyServer, have the students name the files with their names and the name of their constellation – for example, “John Butterfly.html”.
A SkyServer Example
The Rudolph constellation is a simple shape, easy to find with the Navigation tool. There are probably several other Rudolphs elsewhere in SkyServer. This Rudolph consists of six stars. The brightest star in Rudolph (Alpha Rudolphis?) is his right eye, (ra,dec) = (219.73072,0.31204), with g = 14.01.