This section highlights all the information that we came across to deepen our understanding pre-during and post assembly of the telescope. The aim is to put up information that will be helpful as and when we get to learn about something new. Happy Learning!

>> How do I learn the sky?

1. Richard Berry in his book suggests, the best way to learn is via PLANISPHERE, wherein you can dial in the date and time and it will show you the sky at that instant.
2. Following is a list of applications for IOS and Android that we came across, which should help you in navigating the skies

1. Stellarium
2. SkyGuide - notifies you about any transits and also the best objects to look at the sky based on your location
3. Sky Academy - for learning the constellations in the night sky

Android

1. Stellarium
2. Spot the Station - notifies you about the ISS transit from your location
3. Sky Academy - for learning the constellations in the night sky
4. Look4Sat - for tracking the satellites - best for amateur radio astronomers
5. Heavons-Above - for tracking the satellites - best for amateur radio astronomers

>> What is Light Gathering Power (LGP)?

The property of an optical system that tells you how much brighter things will appera than what the human eye can see.

The Light Gathering Power is defined as: $$LGP = \frac{D^2}{d^2}$$

In our case, our primary mirror has a diameter of 150mm and considering if the average human eye lens has a diameter of 6mm in darkness, how much more light will the mirror gather than the human eye?

Answer: $$LGP = \frac{150^2}{6^2} = 625$$ so 625 times more light. The telescope has much larger aperturer than the eye and allows more light which means even stars too faint to be detected by the eye can easily be brightened by the telescope so that they are easy to detect and study.

1. Bright stars in the sky: FIRST MAGNITUDE
2. Faintest visible to naked eye: SIXTH MAGNITUDE
3. For a 6" telescope having 625 LGP, it reaches stars of magnitude 13.5
4. The "Aperture - Diameter of lens or mirror" of the telescope is the most important factor, larger the aperture, more powerful is the telescope.

>> What is Focal Ratio & Magnification of a telescope?

$$FocalRatio = \frac{Focal Length}{Aperture} = \frac{900mm}{150mm} = 6$$

A focal ratio of 6 is an f/6 mirror

$$Magnification = \frac{FocalLengthTelescope}{FocalLengthEyepiece}$$

For a 25mm eyepiece

$$Magnification = \frac{900mm}{25mm} = 36$$

For a 9mm eyepiece

$$Magnification = \frac{900mm}{9mm} = 100$$

• Area of sky visible through an eyepiece = FIELD OF VIEW
• Area of sky covered is = REAL FIELD OF VIEW
• Angle you see when you look into the eyepiece = APPARENT FIELD OF VIEW

>> What is Diffraction & Airy Disk ?

Diffraction: Bending of light near the edges of an obstacle similar to how water spreads out into waves when an obstruction is present in front of it. More on diffraction in telescope can be found >> Diffraction in Astronomy

Airy Disk: A very bright, circular spot of light formed in the center of image which together with the series of concentric rings around is called Airy Pattern.

To deep dive more ...

>> What is Dobsonian Mount & Equatorial Mount?

Dobsonian Mount

The first classic mount for any budding amateur astronomer that only requires screws, glue, plywood and that's it.

The name coming from a renowned amateur astronomer "John Dobson" is best known for promoting awareness regarding astronomy to the common people and thus guiding everyone with low cost & quick mount newtonian reflector telescope.

>> Telescope Building with John Dobson, a must watch video series on building a dobsonian mount.

Equatorial Mount

When you don't want to move your telescope manually, you opt for an equatorial mount which is designed to follow the track the movement of the objects in the night sky. Comparing with a dobsonian mount, equatorial mount offers more sturdy and expensive mount.

The motorized tracking of equatorial mount whose axis align with the earth's rotational axis. The electronics involved gives the opportunity to the user to play around with the overall navigation of the deep sky objects.