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BACKYARD ASTRONOMY. LEARNING THE CONSTELLATIONS. One of best ways to get started is to learn the constellations. Need a star chart, dim flashlight, dark place and unobstructed view of sky. Use star chart according to instructions and date. . Determine which way is north.

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learning the constellations
LEARNING THE CONSTELLATIONS

One of best ways to get started is to learn the constellations.

Need a star chart, dim flashlight, dark place and unobstructed view of sky. Use star chart according to instructions and date.

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Locate a few bright stars , match up with star chart- gives sense of how big a piece of the sky the chart represents.
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Try to id some constellations – first the brighter ones. The Big Dipper ( part of Ursa Major) is a good group to begin with
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Your spread hand held at arm’s length makes a useful scale- for most people this covers about 20 degrees of the sky or the length of the Big Dipper. Use finger widths for smaller distances. Using your hand to scale the sky makes it easy to point out stars to other people. Eg – Star is 2 hands away from the moon at 4 o’clock position.
star lore
STAR LORE
  • Part of every culture. Ancient Greeks, Pawnee indians, Australian aboriginies – all created stories.
  • These star groups do not change except on time scales of tens of thousands of year, so the night sky we see is the same as what they saw. Star lore can link us to the past. Can help to remember the constellations – many of the stories were created as memory devices. People relied on the star positions for many important activities. Baby birds learn to recognize star patterns and use them to help navigate.
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Most familiar star grouping is the Big Dipper. It is an asterism- not a constellation. An asterism is an easily recognized grouping of stars that may be part of one constellation or may incorporate pieces of several. Big Dipper is part of Ursa Major. Asterism of the Summer Triangle spans 3 constellations. Consists of 3 bright stars: Deneb(in Cygnus) Altair (in Aquila) Vega (in Lyra.)
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Big Dipper is a signpost to other asterisms and stars. 2 stars in its bowl are called “pointers” – they point to the North Star, Polaris.
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Polaris lies almost exactly above Earth’s North Pole. It shows no obvious motion during the night. Useful in orienting with a compass.
  • Polaris is at the end of the little dipper- another asterism – and part of Ursa Minor.
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Native Americans story of the Big Dipper- Bowl represents a huge bear, the handle represents 3 warriors in pursuit of the bear. They had wounded it and it was bleeding. Red color of autumn leaves was the blood of the bear when the constellation was low in the sky during autumn months.
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Follow the pointer stars in the Big Dipper past the Little Dipper and Polaris will come to constellations associated with an ancient Greek myth – the story of Perseus and Andromeda. The cast includes King Cepheus, queen Cassiopeia, hero Perseus, princess Andromeda, sea monster Cetus, winged horse Pegasus.
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In ancient days there lived a queen of Ethiopia – Cassiopeia – very beautiful but very vain.
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She and King Cepheus her husband and their daughter Andromeda lived happily until one day the queen boasted that she was more beautiful than the daughters of Nereus – a sea god.
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In punishment for such pride the sea god Neptune sent a sea monster – Cetus- to ravage the kingdom. Cephus was instructed to tie his daughter Andromeda to a rock for the monster to devour.
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Her blood dripped into the sea and turned into Pegasus – the flying winged horse. Depending on the story Perseus rode Pegasus or traveled with winged sandals. He saw maiden’s peril and landed, slaying the monster and delivering the kingdom. They all lived happily ever after. Their astronomical depiction s most easily seen in late autumn – when the brighter constellations are high in the sky.
winter sky orion hunter
Winter Sky- Orion Hunter
  • King of island Chios had a lovely daughter – Merope. His island was filled with savage beasts. He called upon Orion to kill the beasts and make his kingdom safe. Upon completion Orion met Merope and made unwelcome advances. He was punished by being blinded by the King, but after doing penance he regained his sight. When old Orion stepped on a scorpion which stung and killed him. Upon his death the gods placed him and his faithful dogs ( one which chases Lepus the rabbit) in the heavens. There they forever attack the wild bull – Taurus-. Beyond the bull Merope and her sisters run from the Hunter who pursues them each night across the sky. The scorpion was placed on the other side of the heavens so that Orion would never be threatened by it.
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Late summer constellations Bootes and Virgo – Story of Icarius – the first cultivator of grapes for wine. His reward for sharing this knowledge was to be killed by drunken peasants who buried his body under a tree. His dog Maera led Erigone his daughter to the spot where on discovering her father’s body, she killed herself out of grief. Icarius was placed in the sky as Bootes and Erigone as Virgo. The dog Maera became the star Procynon.
amateur astronomy
AMATEUR ASTRONOMY

If you have binoculars or low-powdered telescope you have better equipment than Galileo had. Pleasures of backyard astronomy can range from aesthetic satisfaction, to discovering a new comet or exploding star.

Digital cameras are now used by many for astrophotography.Pg 67

small telescopes
SMALL TELESCOPES
  • Telescopes come in wide range of styles and prices. Many begin with a 3-4 inch reflecting telescope. Uses a mirror to collect and focus the light. The numbers refer to the diameter of the mirror- the larger the number the more light it collects allowing fainter objects to be seen. Also allows view of finer details. With this type of telescope can easily see the moons of Jupiter, rings of Saturn, many star clusters and galaxies. But the later won’t look like pictures in a book because your eyes cannot store up light and are less sensitive to colors in dim light.
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Magnifying power- For most amateurs the maximum useful power is limited by distortions to the light as it passes through the atmosphere. The limit is between 100 and 200 magnification.
  • Need a sturdy mount for the telescope. Vision can be blurred by tiny vibrations cause by wind or the touch of a hand.
star charts
STAR CHARTS
  • To find many of the dim objects with a telescope will need a star chart. Typical chart shows the location of the constellations, the stars,and other objects. Gives some indication of the relative brightness of the star.Many have info about the time of night and season at which the stars are visible.
  • Designed like maps of the Earth. Both are represent something curved on a flat surface. Both use a coordinate grid.
celestial coordinates
CELESTIAL COORDINATES

Similar to the coordinate grid used by navigators. Has one set of lines running east-west on the celestial sphere, parallel to the celestial equator- another set running north-south, connecting one celestial pole to the other. The east-west lines play the same role as latitude on Earth, they are called declination or dec . The north-south lines play same role as longitude and are called lines of right ascension or RA. Declination values run from + 90 to – 90, with 0 being the celestial equator. Right ascension lines divide the celestial sphere into 24 equal zones that are labeled in units of time. The right ascension of an object is given in hours, minutes, and seconds. Because the 360 around the sky is divided into 24 segments, each hour of RA equals 15. The point 0h0m0s of RA is chosen to be where the Sun’s path – the ecliptic- crosses the celestial equator as the Sun moves north.

slide33

Another way to locate a celestial object is to use its altitude and azimuth.Altitude is an object’s angle above the horizon. Azimuth is generally defined as the angle measured eastward along the horizon from North to the point directly below the object. These coordinates are useful for pointing out objects or tracking their motion.

However they have a serious drawback compared to the use of the right ascension and declination: an astronomical body’s altitude and azimuth constantly changes as it moves across the sky .

planetary configurations
PLANETARY CONFIGURATIONS
  • Because planets move across the stellar background astronomers use terms to help describe where they are located at any given time. They describe a planet’s position with respect to the earth and the Sun . This is called planetary configuration.
slide37
If a planet lies in the sky in the same direction as the Sun it is said to be in conjunction. If it lies approximately between Earth and the Sun it is at inferior conjunction. If it lies on the outer side of the Sun, it is at superior conjunction.
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Planets are hard to see at conjunction because they are hidden in the Sun’s glare. In rare occasions may be able to see a planet pass directly between Earth and the Sun. It may be seen as the silhouette against the Sun’s bright disc. This is called a transit. Only Mercury and Venus can transit the Sun as seen from Earth
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A planet’s configuration strongly affects how easily it can be viewed from Earth. When an outer planet is at opposition it is at its nearest to the Earth. The planet is therefore also at its brightest. A planet at opposition rises at sunset. Inner planets are easiest to see when they lie far from the Sun in our sky, so they are not lost in the Sun’s glare. There is a limit to how far from the Sun in our sky an inner planet can be. Mercury can never be more than 28 degrees and Venus never more than 47 degrees as seen on the sky. For this reason Mercury and Venus are usually visible only in the morning or evening sky when the Sun is just below the horizon.
slide43
A planet seen close to the Sun at dawn or dusk is sometimes called the Morning Star or Evening star. When a planet is at its greatest angular separation from the Sun it is said to be at greatest elongation – which can be either western or eastern.
slide44
The time interval between successive planetary configurations of the same type is called the synodic period. This differs from the planet’s orbital period because both the Earth and the other planet move around the Sun. The interval is neither an Earth year nor another planet’s orbital period. The Earth takes about 2 years to catch up to and overtake Mars after an opposition. The Earth overtakes the slower moving, more distant planets more quickly. Ex – Martian synodic period = 780 days
  • Saturnian synodic period= 378 days
your eyes at night
YOUR EYES AT NIGHT
  • The longer you stay outside in dim light the more sensitive your eyes will become and the fainter the stars you will be able to see. This is the result of a physiological change in your eye referred to as a dark adaption.
  • The process takes about 20 minutes to get well established but is undone by even a few seconds exposure to bright light. Once you are dark adapted you should stay away from bright lights for as long as you intend to observe.
slide46
Your eyes also change their sensitivity to color slightly – called Purkinje effect. In full daylight the eye responds best to greenish colors. At low light levels it responds best to slightly bluer colors.
  • Might be able to better see faint objects if don’t look at them directly but instead look a little to one side. This is called averted vision. The center of your field of view is densely packed with receptors designed to allow you to see fine details. They are better at showing fine structure than seeing faint light.