Astronomical Techniques and the Universe

Basic Parts:
- Light enters the tube.
- Passes through an objective lens.
- Light is focused to a single point to create a clear image.
- The focused light rays are viewed by an eyepiece.
A telescope is basically a tube that allows plenty of light to enter.

All lens surfaces must be perfect; otherwise, incoming light will be distorted.
Increasing weight of the lens causes the lens to deform over time.
Difficult and expensive to manufacture large diameter versions of these scopes.
The Yerkes Observatory houses the largest refracting telescope ever built, with a 40-inch diameter and a 63-foot length.

Also called Newtonians.
Reflecting scopes have fat tubes with a parabolic mirror at the bottom, a secondary mirror at the top, and an eyepiece.
Light Path:
- Light from the sky enters the tube.
- The incoming light gets reflected by the bottom mirror back up to the top of the tube.
- A small diagonal mirror bounces the light out to the side of the tube.
- This light is focused to a single point to create a clear image.
- The focused light rays are viewed by an eyepiece.

All radio telescopes are reflecting.
Captures long wavelengths and lower frequencies which visible-light telescopes are unable to capture due to dust.
Radio telescopes are used to view quasars and pulsars.

Pulsar: A highly magnetized rotating neutron star that emits a beam of electromagnetic radiation.
Quasar: A distant galaxy with a fluctuating blaze of light and other radiations coming from its central regions.

Keck 1 and Keck 2: Mauna Kea Observatories, Hawaii; each aperture is 10m (33 ft).
Hale Telescope: Palomar Observatory, California.
The Gran Telescope Observatory: Canary Islands in Spain, a 10.4 m (410 in) reflecting telescope.
3.6 m Devasthal Optical Telescope Observatory: Nainital, India.
Observatory location in the N. or S. hemisphere of the Earth can limit what part of the sky can be observed.

Costs:
- 1978: US$36 \text{ million}
- 1986: US$1.175 \text{ billion}
- 1990: US$4.7 \text{ billion}
- 2010: cumulative costs ~US$10 \text{ billion}
Orbits 353 miles above Earth’s surface.
Observes in the near ultraviolet, visible, and near infrared ( $0.1$ to $1 \mu m$ ) spectra.

Comparison with Hubble:
- JWST is Hubble’s successor.
- Improve resolution and sensitivity over Hubble.
- Gain direct imaging of exoplanets and novas.
- Observe some of the most distant events and objects in the universe, such as the formation of the first galaxies.
- Launch date: December 25, 2021.
Goal: Understand the formation of stars and planets.
*Nova = strong, rapid increase in the brightness of a star
*exoplanets = planets outside of our solar system

The Hubble Space Telescope orbits around the Earth at an altitude of ~353 miles above it.
Webb does not actually orbit the Earth – instead it sits at the Earth-Sun L2 point, nearly 1 million miles away.
Sun-Earth L2 point (L2): a place in outer space where the Sun and Earth’s gravity combine to make a relatively stable point that follows the earth
As the Earth orbits the Sun, Webb orbits with it, but stay fixed in the same spot with relation to the Earth and the Sun.

Webb is currently at its observing spot, Lagrange point 2 (L2), nearly 1 million miles (1.6 million km) from Earth.
It is the largest and most powerful space telescope ever launched.
At the L2 point, Webb’s solar shield will block the light from the Sun, Earth, and Moon.
This will help Webb stay cool, which is very important for infrared telescope.

Location: Webb operates nearly 1 million miles from Earth.
IR + sensitivity: Infrared instruments with longer wavelength coverage and greatly improved sensitivity than Hubble.
Gather more light: Webb has a much larger primary mirror than Hubble (2.5 times larger in diameter, or about 6 times larger in area).
Peer into dust: Designed to look deep into nearby dust clouds to study the formation of stars and planets.
Deep space: Webb is designed to look deeper into space to see the earliest stars and galaxies that formed in the universe.

It is only at infrared wavelengths that we can see the first stars and galaxies forming after the Big Bang.
And it is with infrared light that we can see stars and planetary systems forming inside clouds of dust that are opaque to visible light.

Stars and planets that are just forming lie hidden behind dust that absorb visible light.
Infrared light emitted by these regions can penetrate this dusty cloud and reveal what is inside.

$1 \text{ light year} = 9.46 \text{ trillion km}$ or $9,460,000,000,000 \text{ km}$
$1 \text{ light year} = 5.88 \text{ trillion mi}$ or $5,880,000,000,000 \text{ miles}$
A plane travelling at $965 \text{ km/h } (600 \text{ mph})$ would take $1,000,000 \text{ years}$ to travel one lightyear.
Our crewed spaceships, like Apollo, reach speeds of around $39,400 \text{ km/h} (24,500 \text{ mph})$ . It would still take around $27,000 \text{ years}$ to travel one lightyear.

The James Webb Space Telescope promises to peer back into the making of the first galaxies.