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 Earths
  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 objects 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 objects 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 Suns
  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 planets 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