OBSERVING THE NIGHT SKY

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OBSERVING THE NIGHT SKY

• The Use Of Simple Optical Aids To
• See The Moon, Planets Other
• Bright Objects

Financial support, in the form of an Emeritus
Scientistship to Dr PN Shankar, from the Council
of Scientific Industrial Research is gratefully
acknowledged.
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What we will learn

• How optical aids can help us see better
• About telescopes, binoculars their mounts
• Tips on finding and seeing bright objects
• Observing the Moon and Planets
• Observing other bright objects

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How The Eye Sees An Object

• Light from the object enters our eye through a
  small opening called the pupil.
• The lens in the eye focuses the light to form
  an inverted image of the object on the retina.

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Faint Objects And Object Details

• Because the human pupil is small only a
  limited amount of light can enter the pupil. It
  is hard to see faint objects. Need help!
• If a bright object is far away, its image will
  be small and we will not be able to make out its
  details even though we can see it. Need help!

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What Optical Aids Do

• They help us to see faint objects by gathering
  more light than would otherwise
• enter our small pupils. Act as light buckets!
• They help us to see greater detail by
  magnifying the images of distant objects. Act as
  magnifiers.

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Some Important Optical Aids

• The Refracting Telescope
• The Reflecting Telescope
• Binoculars
• Cameras

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The Refracting Telescope
Light it collected and brought to a focus by a
large objective lens. The eyepiece lens
then magnifies the image seen by the eye.
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A Problem With Refracting Telescopes
Ordinary Lens

• In an ordinary lens white light tends to be
  broken up
• broken up into its constituent colours.
• As a consequence the different colours do not
  get
• focussed at the same point. The image is poor.
• Thus a telescope with an ordinary lens will be
  
• unsuitable for seeing small night sky
  objects.
• ? A good refractor will need an achromatic lens.

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The Reflecting Telescope
? Light is collected focused by a large curved
mirror. ? A flat mirror is used to turn the
light path around. ? The image is magnified by
an eyepiece lens. ? No colour problem (chromatic
aberration)!
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Binoculars
Here the magnified object is seen with both
eyes. Both objectives collect more light than
the pupils. Prisms are used to turn the light
path into the eyes. Once again eyepiece lenses
magnify the images.
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The Galileoscope

• Refractor, 75 cm focal length, 5cm dia
  objective.
• Objective is an ordinary lens, not achromatic.
• Tripod made of bamboo.
• Ball mount made from simple materials.

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The Importance Of Mounts

• It is very important when we use optical aids
  that that they do not shake.
• Mounts are supports which hold instruments in
  place when we use them. They should permit easy
  use of the instrument.
• If you do not have a mount, at least support the
  optical aid on a wall, ledge, window etc. so that
  it does not shake.

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Examples Of Telescope Binocular Mounts
(b)
(a)
(c)
(d)
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Qualities Of Good Mounts

• In a good mount the telescope will be well
  balanced. Easy to use.
• A mount will have 2 axes of rotation, one of
  which will either be vertical or go through the
  Pole Star.
• A mount should have little or no shake.
• Simple mounts should have enough friction so that
  one can hold the object in the eyepiece.

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Need For A Finder Or Gunsight

• It is very important that a telescope or pair of
  binoculars have a finder or gunsight.
• A gunsight could be just 2 rings, one bigger
  (20mm dia), one smaller (10mm dia), spaced say
  25-30cm apart.
• The smaller can be fixed while the bigger one
  should be slightly adjustable.

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Typical Gunsights
Two types of gunsights. The one on the right is
made of sheet metal dimensions need not be
exactly as shown.
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Aligning A Gunsight

• The gun sight should be aligned so that when one
  looks along the sight at a distant object, the
  object will be seen in the telescope. Alignment
  should be done during the day.

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Aligning A Gunsight .....Continued
? Point the telescope at a distant object
and focus it in the eyepiece.

• Now adjust the front ring
• so that the object is
• centred in it when viewed
• through the small ring.
• Fix both rings in place.

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Preparing For Telescopic Observations

• Decide on the objects that you wish to see that
  night.
• Look at the appropriate Star Chart and
  familiarise your self with the star field
  including appropriate pointers.
• If you wish to see a planet find out where it is
  to be found and familiarise as above.
• Choose a good location for your telescope or
  binoculars.

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More preparations

• Make sure that you have a dim, red paper covered
  torch handy.
• Make sure that your telescope and mount are ok
  and that the guide scope is aligned.
• If possible have a convenient chair or seat.
• Make sure that you know which way North and East
  are.

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Night Sky Viewing With A Telescope Or Binoculars

• Locate the part of the sky where you have to look
  for the object that you wish to see.
• Find the object with the naked eye if possible or
  a nearby starfield.
• Use the gun sight to point the instrument in the
  right direction and try to locate the object in
  the eyepiece.
• If not found immediately move the scope around
  and search. If still not found, make sure that
  you are looking in the right direction. Check
  the Star Chart.

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Night Sky Objects For Small Telescopes and
Binoculars

• The Moon its craters
• Venus and Mars
• Jupiter and its Galilean Moons
• Saturn and its rings
• Some bright binary stars
• Some bright open clusters
• A globular cluster - ? Centauri
• The Andromeda Galaxy

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Viewing The Moon

• Be careful the Moon is very bright and can be
  dazzling.
• Best to move from the dark side towards the
  terminator (bright/dark boundary).
• Best view craters and mountains near the
  terminator. Note maria, which are large lava seas.

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Moon View and Galileos Sketches
Telescopic Image
Galileos Sketches
We always see the same face of the Moon!
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Moon Viewing Continued

• Make a sketch starting with the outline of the
  Moon. Mark in the terminator. Sketch in the main
  craters, mountains and maria.
• Good to view on a number of consecutive nights
  and see whether you can recognise features.
• Compare with Galileos sketches!
• Compare with published Moon Maps.

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Viewing Venus and Mars

• Both can be seen with the naked eye and are easy
  objects.
• If possible try to identify and note the phases
  of Venus.
• Mars appears reddish in colour due to iron oxides
  in its composition.
• Difficult to make out Mars polar ice caps.
• Plot, over the year, the orbits of Venus Mars
  against the background stars of the Zodiacal
  Constellations.

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Venus and Its Phases
Venus will appear in your small telescope or
binoculars as in the figure at the left. With
greater magnification you will see the phases.
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Telescopic Views Of Mars
Mars appears reddish even to the naked eye.
Reasonable optics and magnification are needed to
see the polar ice caps.
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Jupiter And Its Galilean Moons

• Jupiter appears as a bright whitish object in
  the night sky.
• It is brighter than Sirius, the brightest star.
• It has rings, not easy to see, and many moons.
• Four of its moons, Europa, Io, Ganymede and
  Callisto
• can be seen even in small telescopes.

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Following In Galileos Footsteps

• Galileo was the first person to see the
  Galilean Moons of
• Jupiter. He used a simple telescope.
• He recorded the motions of these moons which
  appeared
• as star-like points in his instrument.
• Try to follow the motion of these moons over a
  single
• night looking at them every few hours. You
  may not be able
• to see all four of them at a given time!
• ? Make occasional observations over a season.

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Observing Saturn And Its Rings

• To the naked eye, Saturn appears as a bright,
• yellowish object. The rings cannot be seen.
• In a small telescope or binoculars the rings
  appear
• as a disc across the planet.
• ? Observe and record the orientation of the
  rings.

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So far we have only discussed viewing night sky
objects which are bright, e.g. the Moon and the
Planets. We will now consider viewing much
fainter objects
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Hints On Seeing Faint Objects

• If you have difficulty in seeing a faint object,
  say a faint star or star cluster, you can try
  doing two things.
• Darkness adaptation Close your eyes for a couple
  of minutes and then open them. Your pupil would
  have opened this may help!
• Averted vision Dont look directly at the
  position of the object look a little away from
  it. You may then be able to see it!
• These help even when looking though a telescope.

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Observing Binary Stars

• Binary stars are star systems consisting of two
  stars which move about one another.
• To the naked eye a binary star will appear as a
  single star because the system is so far from us.
• An interesting exercise is to try to resolve
  binary systems into their components using an
  optical aid.
• It is hardest to separate stars which are very
  close together or which are very different in
  brightness.

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An Example Zeta Aquarii in Aquarius
The pair 2 secs of arc apart
Location of Zeta Aquarii

• Aquarius is a constellation of faint stars.
  Locating it is itself
• a good exercise!
• ? Aquarii is a binary pair whose stars are of
  almost equal
• magnitude, 4.4 and 4.6.
• ? Is a good test for a telescope with.

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Another Example Beta Cygni
The binary pair 34.6 secs of arc apart
? The principal stars of The Swan bright. ?
Beta (?) is at the head of the swan and easy to
locate. ? The stars are yellow and greenish. A
nice pair to see.
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A Table Of Interesting Binaries
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Training On Binaries

• Choose an easy binary first locate its position
  with the naked eye. Then examine with your
  telescope. Resolved?
• If not, try an easier one.
• Where one or both components are faint, use
  darkness adaptation and averted vision.
• Try improving your instrument or getting a better
  one and train on a number of binaries of
  increasing difficulty. Keep a log.

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Open Or Galactic Clusters
M 34 in Perseus

• An open star cluster is a loose group of stars
  in our
• galaxy that are born and move together.
• They often present a beautiful view to behold.
• There are many open clusters that are barely
  visible
• to the naked eye but can be easily seen with
  aid.
• ? It is enjoyable to locate and view them.

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Two Naked Eye Star Clusters
The Pleiades (M 45)
The Hyades

• These are in Taurus and are easily visible to
  the naked eye.
• The Hyades form a V with red Aldebaran on the
  top left.
• The Pleiades, also known as the Seven Sisters,
  are stunning
• in a pair of binoculars.

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A Well Known Double Cluster
Two stars point to Pole Star
The distorted W Of Cassiopeia
The Perseus Double Cluster

• The double cluster h ? Persei in Perseus is
  visible as a
• hazy patch on clear dark nights.
• ? Will be beautiful in your small instrument.

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Two Easy Star Clusters
M 7 in Scorpius lies between the spout of the
teapot in Sagittarius and the tail of the
scorpion. The background stars are part of the
Milky Way. Visible to the naked eye.
M 44, the Beehive Cluster, is a very well known
one. It appears as a faint patch in the
constellation of Cancer, itself made up of faint
stars. Very nice in a small instrument.
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A Beautiful Globular Cluster

• A globular cluster is a symmetrical
• group of stars that are born and
• move together.
• They are usually made up of very
• old stars, unlike the stars in a
• galactic cluster which are often
• quite young.

• An excellent example of a globular cluster is ?
  Centauri, shown
• above, which lies a third of the way from ? to
  ? Centauri and
• above the line joining them. See Chart 5.
• ? On a clear night it can be seen as a faint
  patch which with a
• small instrument can be seen to be a giant
  globular.

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The Great Andromeda Galaxy

• All the stars and other objects that we can see
  with our
• naked eyes belong to our galaxy, the Milky
  Way Galaxy.
• ? The only object visible to the naked eye that
  does not
• belong to our galaxy is The Great Andromeda
  Galaxy, M 31.
• On a clear, dark night this galaxy is visible
  as a hazy patch
• west of ? Andromedae. Good in a low power
  instrument.

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Locating Seeing The Andromeda Galaxy
? Andromedae
M 31
? Andromedae
? Locate in the above picture the horn in
Andromeda by using the Chart on the right.
The Great Square cannot be seen. ? On a clear
night the night sky is easier than this photo!