Basic_Observations_and_Instruments______

basic observations in astronomy

1. Basic Observations &
Instruments in
Astronomy
HAKIM L. MALASAN
TPOA


Original: Dr. Uwe Trittmann
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2. Basic Astronomy
Topics:
The Basics:
–Basic observations
–Star Maps
–Telescopes

The Night Sky in November

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3. 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, transits, occultations,
etc.)

 All “in the sky”, i.e. on the Celestial Sphere
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4. 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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5. Celestial Coordinates
Earth: Latitude, Longitude

Sky:
•Declination (dec)
[from equator,+/-90°]
•Right ascension (RA)
[from vernal equinox, 0-
24
h
; 6
h
=90°]

Examples:
•Lembang, Indonesia
6.8°S, 107.6°E
•Betelgeuse (α Orionis)
Dec = +7° 24’
RA = 5
h
52
m
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6. 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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7. …depends where you are!
Your local sky – your view depends on your location on earth


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8. Look North
on 40N
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9. Look North
on 21
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10. Daily Rising and Setting
•Due to the rotation of the
Earth around its axis
•Period of rotation:
1 siderial day= 23
h
56
m
4.1
s

•1 solar day (Noon to Noon)
=24
h
•Stars rotate around the
North Star – Polaris
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11. Solar vs Siderial Day
•Earth rotates in
23
h
56
m
, also revolve
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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12. Another Complication: Axis Tilt!
•The Earth’s rotation axis is tilted 23½ 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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13. Position of Ecliptic on the Celestial
Sphere
•Earth axis is tilted w.r.t. ecliptic by 23½
•Equivalent: ecliptic is tilted by 23½ 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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14. The Seasons
•Change of
seasons is a
result of the tilt
of the Earth’s
rotation axis
w.r.t. the plane of
the ecliptic

•Sun, moon,
planets run along
the ecliptic

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15. 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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16. 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)
Pyxis,
Cirnicus
Antlia
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17. Constellations of Stars (cont’d)
Orion as seen at night Orion as imagined by men
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18. 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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19. 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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20. 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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21. 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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22. Reason: All planets move in same
plane!

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23. Motion of the Moon
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24. Phases of the Moon

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25. 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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26. Motion of the Planets
•Along the
ecliptic as
Sun and Moon
•But: exhibit
weird,
“retrograde”
motion at
times
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27. “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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28. The heliocentric Explanation of
retrograde planetary motion
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29. Stellarium
•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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30. Stellarium
Things to observe (cont’d):
•Sun, moon, planets, stars rise (E) and
set (W)
•Where is the highest position of Sun
for the southern hemisphere?
•Planets sometimes move backward
•Moon phases
•Planets have phases, too!



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31. Telescopes
•Light
collectors
•Two types:
–Reflectors
(Mirrors)
–Refractors
(Lenses)
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32. Refraction
Lenses use refraction to focus light to
a single spot

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33. 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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34. Newtonian Telescope
•Long tubes (approx. focal length)
•Open at front
•Eyepiece on side

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35. Schmidt-Cassegrain Telescope
•Very compact & easy to use
•Closed (Corrector plate)
•Reasonably priced
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36. Refractor
•Two lenses -> inverted image
•Long tube (approx. focal length of
objective)
•Usually pretty expensive
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37. 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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38. 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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39. The Night Sky in November
•The sun is at the south shorter nights!

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•Winter constellations are coming up

•Venus, Jupiter, … are easily seen (Saturn?,
Uranus?, Neptunus?)

40. Moon Phases
2015

•11 / 4 (Last Quarter Moon)

•11 / 12 (New Moon)

•11 / 19 (First Quarter Moon)

•11 / 26 (Full Moon)
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41. TURN OFF YOUR LIGHT,
TURN ON TO ASTRONOMY!
Clear skies!