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![Page 1: Basic Observations in Astronomy Classes without Quizzes -Alumni Weekend at Otterbein- June 8-10, 2007 Dr. Uwe Trittmann Welcome to.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649f135503460f94c27aac/html5/thumbnails/1.jpg)
Basic Observations in Astronomy
Classes without Quizzes-Alumni Weekend at Otterbein-
June 8-10, 2007
Dr. Uwe Trittmann
Welcome to
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Basic Astronomy
• Possible topics:– Basic observations – Star Maps– Telescopes– The Night Sky in June– Eclipses
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Basic Observations in Astronomy• Positions of objects (sun, moon, planets, stars …) • Motion of objects
– with respect to you, the observer
- with respect to other objects in the sky
• Changes (day/night, seasons, etc.)• Appearance of objects (phases of the moon, etc.)• Special events (eclipses, transitions, etc.)
All “in the sky”, i.e. on the Celestial Sphere
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What’s up in the night sky? The Celestial Sphere• An imaginary sphere
surrounding the earth, on which we picture the stars attached
• Axis through earth’s north and south pole goes through celestial north and south pole
• Earth’s equator Celestial
equator
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Celestial CoordinatesEarth: latitude, longitude
Sky: • declination (dec) [from equator,+/-
90°] • right ascension (RA) [from vernal
equinox, 0-24h; 6h=90°]Examples:• Westerville, OH 40.1°N,
83°W• Betelgeuse (α Orionis) dec = 7°
24’ RA = 5h 52m
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What’s up for you?
Observer Coordinates
• Horizon – the plane you stand on
• Zenith – the point right above you
• Meridian – the line from North to Zenith to south
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…depends where you are!
• Your local sky – your view depends on your location on earth
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Look North in
Westerville
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Look North on
Hawai’i
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Daily Rising and Setting
• Due to the rotation of the Earth around its axis
• Period of rotation: 1 siderial day= 23h56m4.1s
• 1 solar day (Noon to Noon) =24h
• Stars rotate around the North Star – Polaris
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Solar vs Siderial Day
• Earth rotates in 23h56m
• also rotates around sun
needs 4 min. to “catch up”
• Consequence: stars rise 4 minutes earlier each night
• after 1/2 year completely
different sky at night!
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Another Complication: Axis Tilt!• The Earth’s rotation axis is tilted 23½ degrees
with respect to the plane of its orbit around the sun (the ecliptic)
• It is fixed in space sometimes we look “down” onto the ecliptic, sometimes “up” to it
Path around sun
Rotation axis
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Position of Ecliptic on the Celestial Sphere• Earth axis is tilted w.r.t. ecliptic by 23 ½ degrees
• Equivalent: ecliptic is tilted by 23 ½ degrees w.r.t. equator! Sun appears to be sometime above (e.g. summer
solstice), sometimes below, and sometimes on the celestial equator
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The Seasons• Change of seasons
is a result of the tilt of the Earth’s rotation axis with respect to the plane of the ecliptic
• Sun, moon, planets run along the ecliptic
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The Zodiac throughout the Year
Example: In Winter sun in Sagittarius, Gemini at night sky; in summer sun in Gemini, Sagittarius at night sky
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Constellations of Stars
• About 5000 stars visible with naked eye• About 3500 of them from the northern hemisphere• Stars that appear to be close are grouped together
into constellations since antiquity • Officially 88 constellations
(with strict boundaries for classification of objects) • Names range from mythological (Perseus,
Cassiopeia) to technical (Air Pump, Compass)
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Constellations of Stars (cont’d)
Orion as seen at night Orion as imagined by men
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Constellations (cont’d)
Orion “from the side”
Stars in a constellation are not connected in any real way; they aren’t even close together!
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Understanding and using Star
Maps
• The night sky appears to us as the inside of a sphere which rotates
• Problem: find a map of this curved surface onto a plane sheet of paper
• Let’s explore our turning star map!
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Fixed and unfixed Stuff
• The stars are “fixed” to the rotating sky globe They move from East to West and also
from near to the horizon to higher up in the sky
• The Solar System bodies (Sun, Moon, Planets, Asteroids, Comets) move with respect to the fixed stars
• SSB’s have complicated paths: their own motion is added to the overall motion of the celestial sphere
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Motion of Sun, Moon and other Planets• All major bodies in the Solar System move around ecliptic
• Slow drift (from W to E) against the background of stars
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Reason: All planets move in same plane!
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Motion of the Moon• Moon shines not by its own light but by reflected
light of Sun
Origin of the phases of the moon• Moon revolves around the Earth
• period of revolution = 1 month
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Phases of the Moon
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Phases of the Moon (cont’d)
• Moon rotates around earth in one month
• Moon rotates around itself in the same time
always shows us the same side!
“dark side of the moon” (not dark at all!)
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Motion of the Planets
• Along the ecliptic as Sun and Moon
• But: exhibit weird, “retrograde” motion at times
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“Strange” motion of the Planets
Planets usually move from W to E relative to the stars, but sometimes strangely turn around in a loop, the so called retrograde motion.
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The heliocentric Explanation of retrograde planetary motion
See also: SkyGazer
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SkyGazer
• A computer program that simulates the vision of the sky during day and night
Things to observe:• Set your position on Earth: observe how view of
sky changes as you move E,W, N,S• Note the distribution of sunlight on Earth!• Rotation is around Polaris which is not in zenith
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SkyGazer
Things to observe (cont’d):• Sun, moon, planets, stars rise (E) and set
(W)
• In the southern hemisphere the sun is highest in the north
• Planets sometimes move backward
• Moon phases
• Planets have phases, too!
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Telescopes
• Light collectors
• Two types:– Reflectors
(Mirrors)– Refractors
(Lenses)
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Refraction
• Lenses use refraction to focus light to a single spot
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Reflection• Light that hits a mirror is
reflected at the same angle it was incident from
• Proper design of a mirror (the shape of a parabola) can focus all rays incident on the mirror to a single place
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Newtonian Telescope
• Long tubes (approx. focal length)
• Open at front
• Eyepiece on side
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Schmidt-Cassegrain Telescope (CAT)
• Very compact & easy to use
• Closed (Corrector plate)
• Resonably priced
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Refractor
• Two lenses -> inverted image
• Long tube (approx. focal length of objective)
• Usually pretty expensive
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Binoculars
• Erect image -> good for terrestrial viewing• Prisms needed to produce erect image• Typical specs: 8x60, means magnifies 8x
and objective lens is 60 mm in diameter
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A good starting point
• A pair of binoculars and a star map will keep you busy for a long time – anywhere!– constellations – Planets– Moon– Orion nebula– Andromeda Galaxy– star clusters– …
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The Night Sky in June
• The sun is at its highest -> shortest nights!
• Summer constellations are coming up: Hercules, Scorpius, Ophiuchus (Snake Bearer), Snake
lots of globular star clusters!
• Center of the Milky Way in Sagittarius
• Jupiter, Saturn & Venus are easily seen
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Moon Phases
• 6 / 8 (Last Quarter Moon)
• 6 / 14 (New Moon)
• 6 / 22 (First Quarter Moon)
• 6/ 30 (Full Moon)
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Today at
Noon
• Sun at meridian, i.e. exactly south
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10 PM
Typical observing hour, early June
• no Moon
• Jupiter• Pluto
(experts only)
Saturn
Venus
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South-West
Virgo and
Comawith the
Virgo-Coma galaxy cluster
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Virgo-Coma
Cluster
• Lots of galaxies within a few degrees
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M87, M88 and M91
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Zenith
• Big Dipper points to the north pole
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South– Canes Venatici
– Corona Borealis
– Bootes
– Serpens
Globular Star Clusters:• M 3• M 5• M 13
M 5
Galaxies: • M 51• M 101• M 64 (Bl. Eye)
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South-East
– Hercules– Ophiuchus– Serpens
Globular Star Clusters:• M 13• M 92• M 12• M 10 …
M 5Summer is Globular Cluster time!
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M13: Globular Cluster
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South-East
– Ophiuchus– Serpens– Scorpius
Globular Star Clusters:• M 4• M 19• M 62• M 80 …
M 5Summer is Globular Cluster time!
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Appendix: Eclipses
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Eclipses
• One celestial object hidden by other or in the shadow of another
• Solar eclipse: sun hidden by the moon• Lunar eclipse: moon in earth’s shadow (sun
hidden from moon by earth)• Also: eclipses of Jupiter’s moons, etc.• Most spectacular because moon and sun
appear to be the same size from earth
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Solar Eclipses
• Umbra – region of total shadow• Penumbra – region of partial shadow• Totality lasts only a few minutes!• Why isn’t there a solar eclipse every month?
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Solar Eclipse
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Solar Corona
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Question
Why isn’t there an eclipse every month ?
Answer: because the Moon’s orbit is inclined w.r.t. the ecliptic
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Lunar Eclipses Moon moves into
earth’s shadow…
…and out of it
(takes hours!)
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Partial Eclipse
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Not an Eclipse !
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Towards Totality
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Almost total…
![Page 63: Basic Observations in Astronomy Classes without Quizzes -Alumni Weekend at Otterbein- June 8-10, 2007 Dr. Uwe Trittmann Welcome to.](https://reader036.fdocuments.in/reader036/viewer/2022062321/56649f135503460f94c27aac/html5/thumbnails/63.jpg)
Totality
Totality