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Your first Sky Observation of Moon with Telescope

For any amateur Night sky observer after receiving a telescope, the first target to observe in the sky would be the moon. The moon is the second brightest celestial object in the sky, after the sun.

This blog talks about some important tips that you need to follow before your first telescopic encounter so as that you could make your observation enjoyable.

Know about your Moon

  • Moon is a nature satellite of earth.
  • In our solar system there are 173 known natural satellites, these natural satellites orbit in the 6 planetary satellite systems.
  • Generally moon word is also used when we describe the nature satellite of other planets also, for example we say there are four Galilean moons of the Jupiter namely Io, Europa, Ganymede, and Callisto.
  • But when we talk about Moon, we simply mean, only and only one natural Satellite of Earth, which is our Moon.

Solar system planets and their natural Satellites:

 Planet Natural Satellite
 Mercury  0
Venus 0
Earth  1 Moon
Mars  2 Phobos & Diemos
Jupiter 67 known moons of Jupiter
Saturn  62 moons
Uranus  27 known moons
Neptune  14 known moons
  • Even though moon is the closest and biggest celestial object in the night sky, still it is far away from us ,384,400 km away from us !
  • There is no atmosphere on the moon ,temperature is extremely cold -250º and very hot 250ºF.
  • That’s why astronauts had to wear special spacesuits when they land on the moon. This special suite protects them from the extreme temperature and provide them oxygen

Effect of Moon on Earth

The Moon’s gravitational influence produces the ocean tides, body tides, and the slight lengthening of the day. Current moon’s orbital distance is about 30 times the diameter of earth, making its apparent size in the sky almost same as that of the Sun. Moon covers the Sun completely during total solar eclipse.

WHY WE SEE ONLY ONE SIDE OF THE MOON

The Moon and the Earth are tidally locked which means moon rotates about its axis at the same rate as the Moon orbits the Earth, this phenomenon is called Gravitational Tidal locking. Therefore we see only one side of the moon which is called the near side of moon and the other side which is not visible from earth is called Far side of the moon .To understand this concept in a better way you can watch this video

MOON PHASES

The most prominent thing about our moon is that it is quite big that we can see detail without any optical instrument. When moon revolve around the Earth, the sun’s light falls on it from different angles which results in the phase of moonlit is basically the illuminated (sunlit)portion seen by any observer on earth.

The lunar terminator is the boundary between the illuminated and darkened hemispheres, all parts of the Moon see around 14.77 days of sunlight followed by 14.77 days of “night”

Phases of Moon        Image courtesy http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit2/phases.html

  • New Moon : This is the phase when the moon is not visible in sky, since the far side is been illuminated by the sun, and the near side is in total darkness. During this phase Moon and sun rise together in the sky
  • Full Moon: During full moon we see the entire moon as the near side is been fully illuminated. Full Moon rises after sunset in the sky.
  • Quarter Moon : First Quarter and Last quarter occurs when Sun, Earth and Moon are aligned at right angle. Half side is illuminated and half side is dark.
  • Waxing & Waning : Waxing means getting bigger every night Waxing Crescent comes just after New Moon and Waxing Gibbous comes just before Full Moon
  • Waning means getting smaller every night ( decreasing illumination).Waning Gibbous comes just after Full Moon and Waning Crescent comes just before New Moon
  • When the moon’s surface is illuminated by sun more than half it is called Gibbous

HOW TO CHOOSE WHEN TO VIEW MOON

Most people think that the best time to observe moon is full moon, but this is wrong, in fact this is the worst time to observe .During full moon the sunlight falls directly straight overhead on the moon’s surface and it look like desert .We won’t be able to observe moon’s features like craters, Mare, mountains, rays and rills during full moon. The best time to observe moon is at the two quarters when the sun’s light is falling on it either from right or left.

Whenever you are observing the moon, you need to first check the moon phase (illumination should be greater than 10% and less than 60%) and second important thing is the moon set time .You never see all the moon phases at all times, for example waxing and waning   crescent can’t be seen at midnight, last quarter cannot be seen at sunset and you won’t see a full moon during daylight since full moon rises as the sun sets.

Moon rise and moon set depends on the Sun-Earth –Moon configuration, when a observer view from the surface of the earth.For this you can use website like www.timeanddate.com and Follow the steps

When to See Moon Step 1

When to View Moon Step 2

  • Select the month and year you would like to observe the moon.

Moon Observation Chart

  • The best time to observe the moon through telescope is when the illumination is more than 10% and less than 60%.

Other site you can use is http://www.astronomy.com/

There are mainly two main types of telescope: REFRACTOR TELESCOPE which uses lenses to collect and focus light; and REFLECTOR TELESCOPE which uses mirrors to collect light. Telescopes are always judged by their aperture that is the diameter of the Objective lens or Mirror .When people refer small telescope ,it simply means refractors (telescopes under 75mm or 3 inch).Telescopes with apertures more than 175 mm or 7 inches are usually reflectors, since large mirrors can be made more cheaply than lenses.

Setting Up of the Telescope for the observation

What kind of place to set up the telescope?

  • A place where there is clear sky and no clouds
  • Minimal lighting from the nearby areas like streets or buildings or houses.
  • A transparent sky without clouds so that light does not get absorbed.
  • Stable air ,no wind to avoid blurring

Mounting of the telescope

Our previous blog talks about different mounts

  • Altitude –Azimuthal: The simplest type of telescope mount allows the telescope to be moved up and down(in vertical or altitude ,angle varies from 0° to 90 ° )and left to right (in horizontal, or azimuth angle varies from 0 ° to 360 ° ).This mounting permits the observer to follow objects by simple motion of the telescope in vertical and horizontal.
  • Equatorial: As the earth rotates on its axis, the object in the sky change their position with time. The task of this telescope mounting is to compensate for the Earth’s rotation and allows observer to track moon, The equatorial mount has north-south “polar axis” tilted to be parallel to Earth’s polar axis that allows the telescope to swing in an east-west arc, with a second axis perpendicular to that to allow the telescope to swing in a north-south arc.

Image courtesy http://www.skyandtelescope.com/astronomy-equipment/the-art-of-using-a-telescope/

Azimuth & Equatorial Mount

OPTIMUM EYEPIECES AND MAGNIFICATION.

REFRACTOR TYPE

The smallest refractors, of 50 to 70 mm aperture, will show the Moon’s craters and dark lowland ‘seas’

REFLECTOR TYPE

Magnification is the most commonly known term linked with a telescope but it is misleading too. Magnification can be understood as enlarging the relative picture of an object but high power doesn’t mean good observation.  Although high power means larger appearing object but it also means more spreading of light further fainting the object’s image. So one must look for an optimized value of magnification for the scope rather than blindly looking for higher numbers. Also the highest practical power of the scope is limited by its aperture size .This can be better understood using this mathematical relation

Magnificatin & Focal Ratio

This equation simply relates the Magnification for a telescope with the focal lengths of its objective and eyepiece lens.

Magnification =Focal length of Objective lens/Focal length of the eyelens

There is an inverse relation between Magnification and focal length of eyepiece.this means smaller the focal length of eyepiece,larger will be the magnification and vice versa .Since Moon is a bigger object in the night sky we do not need higher magnification because magnification and Field of view is inversely related that is you need to view the entire moon and its crater it is better to choose eye piece with a larger focal length. Usually telescopes are provided with 12,5 mm and 25 mm eye piece .So it’s better to choose 25 mm over 12.5 mm for better field of view .A low magnification will show you the whole moon and gives you big and better picture

Align your telescope using finder scope; you can refer our blog to know how to align your telescope. Since moon being the biggest object in the sky, It is quite easy to locate it. Before looking at the moon with your telescope, take a good look at it with your naked eyes. Move your telescope towards it and try to find the moon in the eye piece by adjusting the knob of the telescope.

Now you can observe the craters on the moon and other moon features! one thing you need to note is that our earth rotates at a speed of 465 meters/second ,every time you need to adjust the knob to keep the moon in the Field Of view.

OBSERVING APOLLO LANDING SITE

July 29, 1969 is considered as one of the most important dates in the history of Astronomy . It’s when America’s Apollo 11 astronauts landed on the moon. The first man to walk on the moon was Neil Armstrong. His famous word after landing on the moon: “That’s one small step for       man, one giant leap for mankind

Landing Site of Moon Image Courtesy : http://www.express.co.uk

The first quarter phase of the moon is the perfect time to observe the lunar surface features and check out some of Apollo landing sites.

Moon Landing Sites : Find from Telescope

Recommended Posts for Astronomy for Kids :

  1. Anatomy of Sun
  2. View Sun From Telescope
  3. Hands on Activity for Kids : Make a Comet
  4. Things to Know about Telescope