Telescope

what happens to our eyes at night?

at night our eyes dilate in order to see more light which means our vision will improve

what is light gathering power?

Light gathering power refers to a telescope's ability to collect light from faint objects, enhancing visibility and detail in astronomical observations.

what is the formula for light gathering power (LGP)?

LGP ratio=(D_b/D_a)² where Db is the diameter of the big telescope and Da is the diameter of the small telescope.

what is the formula for area?

The formula for area, particularly for a circle, is A = πr², where A is the area and r is the radius.

what are reflectors and refractors?

Reflectors are telescopes that use mirrors to gather and focus light, while refractors use lenses to bend and direct light.

what is a refracting telescope?

A refracting telescope uses lenses to bend (refract) light and form an image.

• The objective lens has a focal length f_o​ and brings light to a focus.

• The eyepiece lens has a focal length f_e​ and magnifies the image.

The magnification M of a refracting telescope is given by:

M = f_o/f_e

f_o​ = focal length of objective lens (large)
f_e​ = focal length of eyepiece lens (small)

How it works:

• The objective lens forms a real image at its focal point.

• The eyepiece lens then acts like a magnifying glass to enlarge that image for your eye.

what is the similarity between retraction and reflection?

both are used to gather and focus electromagnetic radiation . in both cases, the image formed at the focus is viewed with an eyepiece

what is the angular magnification of a telescope?

it depends on the focal lengths of the objective lens and eyepiece, the formula is M = fo / fe, where M is angular magnification and the negative is inverted

why is magnification limited by LGP?

magnification needs more pixels → more light and if not enough light is collected magnification is limited

how large can a refracting telescope be?

they can’t be larger than 60-90cm in aperture because of the weight of the lens and support issues, chromatic abberation, light absorption and imperfections, and the length of it

how is image formation reversed?

In telescopes, image formation is reversed due to the arrangement of lenses. The objective lens produces an inverted image that is further inverted by the eyepiece, resulting in an upright final view for the observer.

what is aperture of lens?

it’s exactly like the pupil of an eye, it functions to control the light amount. it adjusts the size of the opening through which light enters the telescope, affecting brightness and resolution of the image.

what does exposure time cause?

Exposure time causes increased brightness and detail in images captured by telescopes. Longer exposure times allow more light to accumulate

what is the rate of light gathering long exposure?

it depends on LGP = area x time (exposure time)

what is the interference of waves and how does it work?

Interference of waves happens when two or more waves meet at the same place and combine to form a new wave.

There are two types:

• Constructive interference:
  ✅ Waves add together to make a bigger wave (when crests meet crests).

• Destructive interference:
  ✅ Waves cancel each other out to make a smaller wave or even no wave (when crest meets trough).

How it works:

• Waves overlap.

• Their amplitudes (heights) are added together at each point.

what is resolving power?

the angular resolving power is the smallest angle (angular separation) between close objects that can be seen clearly to be separate, it’s the ability to distinguish close or nearby objects from each other

what is resolution?

the ability of optical system to distinguish between closely spaced objects is limited because of the wave nature of light

what is Rayleigh’s criteria?

Rayleigh’s criterion states that two light sources are just barely distinguishable when the central bright spot of one overlaps the first dark ring of the other..

how can resolving power be measured?

Resolving power can be measured by examining the smallest angle at which two separate light sources can be distinctly identified, typically using a test object such as a double star or a pair of closely spaced lines.

what is atmospheric turbulence?

Atmospheric turbulence refers to the random, chaotic motion of air in Earth’s atmosphere, caused by temperature differences, wind, and pressure changes. It distorts the light from stars and celestial objects, making them appear to twinkle and limiting the sharpness of ground-based telescope images.

what is the spitzer?

Spitzer refers to the Spitzer Space Telescope, an infrared telescope to study the universe by detecting heat (infrared radiation) from stars, planets, and galaxies, especially those hidden by dust.

what is chandra-x?

designed to capture x-ray images → important to target objects like neutron stars, black holes…

The girl is using a telescope that has objective lens with focal fo= 90 cm. The magnification obtained when she uses an eye piece lens with focal fe = 6 cm is = ?

M = f_o/f_e so fo is 90 cm and fe is 6cm → 90/6 is 15 so the magnification is 15x

What types of radiation passes through Earth and which can only be seen in space?

Visible light passes through Earth (colours shown in diagram) and radio waves also pass through while ultraviolet, x-rays, and gamma rays can only be observed from space.

What is the difference between a refracting and reflecting telescope?

Key Differences:

• A (Reflector): Mirrors, better for big telescopes, no chromatic aberration (color distortion).

• B (Refractor): Lenses, simpler design, but lenses can cause color distortion.

What do we call when light rays converge to one point?

A focal point is the point where light rays meet after being refracted or reflected.

the car has two headlights: however, looking at a car coming from far away, we see only one source of light and not two!

1) What do we call this phenomena?

2) Explain why do we see the two sources of light as one source. What is the condition/requirement needed to see them as separate sources?

1) What do we call this phenomenon?
✅ Answer: Diffraction (or Limit of Resolution)

2) Why do we see two lights as one?

• The two headlights are very close together compared to the large distance from the car to us.

• Their light waves overlap and we can't distinguish them as separate sources.

Condition/Requirement to see them separately:
✅ The angular separation between the two lights must be greater than the telescope or eye's resolution limit.
✅ Basically, the two lights must be farther apart or we must be closer

1) When we try to take image of stars with our cell phone camera none will show up in the image! why?

2) how it was possible in diagram (A) to capture images of some stars. explain how?

3) in diagram (B) stars have trails, why? How is it possible to eliminate that?

1) Why don’t stars show up in a cellphone photo?
✅ Cellphone cameras have small lenses and short exposure times, so they don’t gather enough light from faint stars.

2) How was it possible in Diagram A to capture stars?
✅ Large telescope mirrors collect a lot more light and use long exposure times to make faint stars visible.

3) Why do stars have trails in Diagram B?
✅ Because of Earth’s rotation, the camera sees the stars moving across the sky during long exposure.

How to eliminate star trails:
✅ Use a motorized mount that tracks the stars (moves the camera at the same speed as Earth’s rotation).

what are adaptive optics?

Adaptive optics are technology used in telescopes to correct for distortions caused by Earth's atmosphere, improving image quality of astronomical objects.

what are 3 factors to improve observation by telescope?

more light (larger telescope and longer exposure), smaller angular resolution (OR) larger telescope since light is wave with interference or diffraction effect, and atmospheric effects that are reduced by high altitude, adaptive optics, or by going to space

what are gravity waves?

Gravity waves are ripples in spacetime caused by the acceleration of massive objects, predicted by Einstein's General Theory of Relativity. They are detectable through their effects on other objects in the universe, such as merging black holes or neutron stars.

what is angular resolution? is the smaller the better?

Telescopes can make out finer details than our eyes can since telescope can have smaller angular resolution. The smaller the angular resolution θR the better!

list 3 ways that the earth’s atmosphere hinders astronomical observation

it blocks light from wavelengths - stopping it from ever reaching the ground, it scatters human-generated light (light pollution), and the constant movement of the air