Astronomical Scales (Lectures 2/3)

Astronomical unit (AU)

distance from Earth to Sun

Equation relating distance, speed, and time…

Distance= speed x time

Light years

distance light travels in 1 year

How is distance measured in the solar system?

measured by radar

How is distance measured in the Milky Way (between stars)?

stars’ distances are measured using stellar parallax

How are distances between galaxies measured?

measured using standard candles

What is a stellar parallax?

The apparent shift in position of a nearby star compared to a background/distant stars.

We compare the position of a distant star to our Earth as it rotates around the sun

What are standard candles?

Supernovas
Compare how bright something is supposed to be to how bright it appears to you in the moment to measure the distance.

Scientific notation

Number x 10^power

What is the distance from the Earth to the Sun?

1 AU

What is the mass of the sun?

2×10³0 (1 Msun)

Age of the Earth?

4.5×10^9 years (billion years)

What does prefix tera mean?

Trillion (terabyte)

What does prefix is giga mean?

Million

What does the prefix pico mean?

10^-12

What does the prefix femto mean?

10^-15

How far is the Moon from the Earth?

1 light second away

How far is the Sun from the Earth in time units?

8 light minutes away

A huge group of many galaxies is called…?

Clusters of galaxies

Clusters of galaxies form…?

Enormous super clusters of galaxies

What is the farthest that human beings have traveled in space?

The moon

Where is most of the mass in the solar system?

The sun

What two elements make up our sun?

Mostly hydrogen and helium

Why does the sun glow?

Due to nuclear fusion of H and He at its core

Where is the Kuiper belt located?

Beyond Pluto; 30-55 AU from the Sun

What is in the Kuiper Belt? What does it consist of?

70,000 comets (<100 km) that orbit in the same plane as the planets. Everything is made out of ice because of the cold and distance from the sun

Where is the furthest that a human-made spacecraft has traveled?

Beyond the Kuiper Belt

Where is the Oort Cloud located?

Beyond the Kuiper Belt; extends as many as 50000 AU

What is the Oort Cloud made up of?

Trillions of comets that all have random orbits (not like planets or moons)

How do we know distances in our Solar System?

We bounce light off them and time how long it takes the light to make the round trip (mostly radio waves – Radar)

What is the fastest anything can travel?

Speed of light; a fixed and constant speed

What is the speed of light?

c = 300,000 km/s

Why are telescopes like time machines?

It takes light time to travel across the Universe, so the further the object is the further back in history you see it (bc light travels longer)

What is the closest star to us?

Proxima Centauri; 4.2 light years away (so if we look at it through a telescope we will see 4.2 light years later)

How many stars can you see in the sky at night?

A few thousand

What is a " Solar neighborhood"?

Bodies within 100 light years of us

How does a stellar parallax work?

As you move quickly past something, things close to you change/move very quickly, while objects far away barley move

Distant stars have small parallaxes and closers stars have larger parallaxes

Parallaxes are apparent shifts in positions of nearby stars. Which measurement would be key to get a really precise measurement of parallax?

(A) The precise position of the object on the sky.

(B) The precise apparent brightness of the object.

(C) The precise color of the object.

(D) The precise chemical composition of the object.

A

What is a local group?

A local group of galaxies consists of 100 or so galaxies, may include not full-sized ones (ex: the Milky Way and Andromeda are part of the same group)

What are Magellanic Clouds

two neighboring dwarf irregular galaxies which orbit the Milky Way

How far is the Andromeda Galaxy from us?

2.5 million light years away

What are clusters of galaxies?

thousands, tens of thousands, or more full-sized galaxies grouped together

Superclusters?

Clusters and groups of galaxies together

How many galaxies are there in the Universe?

Many billions