Studying the universe

Studying the universe

What is astronomy? A branch of science that deals with study of stars, planets, the universe as a whole The idea is that we live in a clockwork universe and is governed by laws that are that same in all places (literally universal) and that can be discovered Related to cosmology, which is the study of the origins of and development of the universe

Studying the universe doing astronomy Nearly all (but not exactly all) of our methods of studying the universe are about analyzing some kind of EMR In Astronomy, we use telescopes to study EMR coming from an object to analyze its Temperature Composition Structure Distance What it may be interacting with

A telescope is a time machine Light has a finite speed (3.0 x 10 8 m/s) The more distant the object, the longer it s taken for its light to reach us Light takes ~ 1 second That s to 5.9 reach x 10 12 miles, the or moon 5,900,000,000,000 miles We see the sun as it was 8 minutes ago The distance light travels in one year is called a light year, and is 9.5 x 10 15 m The nearest star, Proxima Centauri, is 4.24 light years from earth! How far away is the most distant?

Refractor telescopes Were not invented by Galileo, but Galileo is thought to be the first person to use them for astronomy Magnification is focal length of objective X focal length of eyepiece

Pros and cons of refractors Cheaper refractors with one lens do not bring all colors to the same focal point Bright objects look like they are surrounded by a rainbow Can be corrected by adding additional lenses/better quality lenses but that is expensive! Good refractors produce extremely sharp images Red, green, and blue do not come to focus at the same point

Modern refractor Mine A three-lens (triplet) design with extremely low chromatic aberration

The Newtonian Reflector Designed by Isaac Newton, purpose was to use polished mirrors to reflect light into a focal point rather than using lenses to bend light into a focal point this eliminates the chromatic problems of refractors

Modern Newtonian But Newtonians can be big and with the eyepiece at the top it can be hard to use if the telescope is pointed up

Virgo galaxy cluster (by me) Using a Canon camera and 6 aperture Newtonian Telescope

Advances in telescope design compound telescopes Produces an effective focal length much longer than equivalent sized refractors or reflectors, so much more magnification is possible!

Saturn, using a 9.25 aperture compound telescope by me

The Hubble ST, a space-based compound telescope

Seeing beyond the visible EMR Modern astronomers still use visible light, but may also use X-ray emission, Gamma emission, infra-red, microwave and radio.

Longer wavelengths need a bigger net

The Very Large Array (VLA), New Mexico

The next generation James Webb JWST will launch in 2018 and be in orbit beyond that of the moon. The main mirror will be 5 X that of the Hubble ST. The mirror is highly polished Beryllium. The device is designed primarily as an infra-red telescope

Webb versus Hubble

Wide-field Infra-red Survey Explorer (WISE) Measured heat produced by objects in Universe, required onboard supply of liquid Helium!

WISE data on galaxies

Near-Earth Object WISE - NEO-WISE

Understanding the universe How big is the cosmos?

Measuring distance 1 - Parallax Early astronomers attempted to use parallax the apparent difference in position of an object when viewed from different angles to measure cosmological distances They SEVERELY underestimated actual differences, and were unable to make any meaningful measurements With better telescopes now such as space telescopes, these measurements can now be made

Measuring distance 2 standard stars Imagine you are observing two perfectly identical candles. Everything about them is identical except One is significantly brighter than the other What is the most likely reason one is brighter? One is closer than the other! The brightness/dimness of identical sources of light varies directly with distance

Finding a standard star To make the comparison fair, we have to locate stars that we would expect to be equally bright Stars come in just about all shapes, sizes, and temperatures, so how do we locate a standard? We find a special kind of dying star an exploding star called a super nova

Supernova in spiral galaxy When these explode, we measure how bright they appear, and from that compute their distance. So we directly measure the distance to this galaxy

But a problem turns up when we look at extreme distances

Red shift The light from very distant objects is redder than it should be But light is a wave, like sound, and this understanding changed people s picture of the universe The frequency of the sound a moving object changes depending on whether objects is approaching or leaving Light might behave similarly

The Doppler effect

The Doppler effect causes red shift

Red shift

What red shift tells us Most objects in the universe seem to be receding from us and from each other in all directions The more red, the farther away AND the greater the speed at which they seem to be receding! The universe is expanding!

Evidence of an expanding universe There is not a single direction or angle you can point a telescope (or your eyeballs) at where is Invisible there to an our eyes but not to radio absence of stars telescopes! So if there is a star in literally every direction, why is the night sky dark? Space appears dark because the light from distant stars has been red-shifted beyond the ability of our eyes to see it because the universe is expanding If the universe was not expanding, light from stars would not be red shifted, we would see stars everywhere, and the night sky would be the opposite of black

Georges Lemaitre said if the universe is expanding, it must have expanded from somewhere in the distant past... at some point in the distant past, the universe was highly compressed. He called this condition a primeval atom from which the universe exploded outwards and is still expanding outwards today Bigger questions

But Fred Hoyle, noted astronomer and physicist didn t like that idea mainly because Lemaitre was (in addition to being a top-rate physicist) a Catholic Priest Hoyle mocked Lemaitre s hypothesis, referring to it as a Big Bang Hoyle liked the idea of a steady state universe But that s crazy!

The age and size of the universe Everything we see today is consistent with Lemaitre s views The term Big Bang was originally meant to make fun of Lemaitre s theories, but is now the accepted explanation of the universe s origins The most red-shifted light we see is about 14 billion light-years distant, so we consider the age of the universe to be ~ 14 Billion years old