Backyard Astronomy

1. Backyard Astronomy Arny, Essay 1

2. Learning the Constellations • Tools of the Trade • Star chart with directions on how to hold it for a given day and time • A dim flashlight • A dark area with an unobstructed view of the sky • Getting Started • Determine north using a compass if necessary • Locate a few bright stars matching them with the star chart • Identify a few of the major constellations • Star hop to other stars and constellations using your extended hand and clock directions

3. Star Lore • Star lore is a part of most cultures and may have been used as an aide to remembering the constellations, an especially important need for farmers and navigators • Since constellations do not change much over thousands of years, star lore also provides a connection to the past • Asterisms are also important collections of stars in the sky – For example: • Big Dipper, Little Dipper and the “pointers” • Summer Triangle

4. Star Lore • Some stories • North American natives and the Big Dipper • Greek mythology near the Dippers: Cepheus (king of Ethiopia), Cassiopeia (the queen), Andromeda (their daughter), Cetus (a sea monster), Perseus (the hero), and Pegasus (his winged horse) • Another: Orion the Hunter, his hunting dogs (Canis Major and Canis Minor), a bull (Taurus), a rabbit (Lepus), the sisters (Pleiades), and a scorpion (Scorpius)

5. Amateur Astronomy • Basic Equipment • Binoculars or low-powered telescope with motor drive • 35-millimeter camera, high-speed film, cable release, and a tripod • Basic Amateur Astronomy • Long exposures and “star trails” • When to use a “drive” system to prevent star trails • Variable star observing and comet hunting

6. Small Telescopes • Small telescopes come in a wide range of styles, but generally you get what you pay for • Reflecting telescopes, which uses a mirror to collect and focus light, are popular • The larger the mirror, the fainter an object can be for the eye to detect • Larger mirrors also also finer detail to be seen • Maximum useful magnification is limited to about 100 to 200 due to atmospheric distortion • A sturdy mount is needed to prevent image jiggle • Consult your instructor or an experienced amateur astronomer before buying a telescope

7. Star Charts • A telescope allows one to look at objects (galaxies, clusters, and nebulas) too faint for the eye to see • To find these objects requires a good star chart • Charts are designed like maps allowing the user to find objects relative to other brighter objects for a given time and day

8. Celestial Coordinates • A coordinate grid on a star chart is similar to that used by navigators • One set of lines run east-west on the celestial sphere, parallel to the celestial equator, and are called lines of declination (or “dec” for short) • Another set of lines run north-south, connecting one pole to the other, and are called lines of right ascension (or “RA” for short) • Dec is similar to latitude on the Earth’s surface, and RA is similar to longitude • Dec values run from –90º to +90º, with 0º being the celestial equator • RA values run from 0h 0m 0s around the celestial sphere in 24h and back to the origin, which is that point where the ecliptic crosses the equator in Spring • 1 hour of RA equals 15 degrees

9. Celestial Coordinates • The Horizon Coordinate System • Altitude is an object’s angle above the horizon • Azimuth is the angle measured eastward along the horizon from North to the point directly below the object • Horizon coordinates are useful for pointing out objects locally • An object’s horizon coordinates change as the object progresses across the sky, whereas its RA and dec coordinates do not

10. Planetary Configurations • Astronomers have invented terms to help describe where planets are located at a given time with respect to an observer and the Sun • A planet located in the same direction as the Sun is said to be at conjunction • If the planet is approximately between the Sun and us, it is said to be at inferior conjunction • If the planet is located beyond the Sun, it is said to be at superior conjunction • If the planet is directly in line with the Sun, so that it is silhouetted against the Sun’s bright surface, the event is called a transit • A planet located directly opposite the Sun in the sky is at opposition - an outer planet is nearest Earth at opposition

11. Planetary Configurations • More Terminology • An inner planet is easiest to see at greatest elongation, either eastern or western • A planet seen near the Sun at dawn or dusk is sometimes called the morning star or evening star • The time period between successive planetary configurations is called the synodic period (not to be confused with a planet’s orbital period)

12. Your Eyes at Night • The longer you stay in dim light, the more sensitive your eyes become to faint objects • This physiological change in your eye is called dark adaptation • The process of dark adaptation includes widening of the pupils and chemical changes to the retina • The process can take 20 minutes, but can be ruined with bright light in seconds • Color sensitivity also changes at lower light levels, becoming more sensitive to blue versus green in daylight • Sensitivity to light also increases through averted vision, looking slightly to the side of a faint object