Exam Study Notes

Announcements/Updates

  • Assignment #0 is due on Monday, May 12 at 4:59pm
  • Office hours:
    • Virtual - Mondays 2-3pm. Zoom link is on the syllabus
    • In-person- Wednesdays 2-3pm, 60 St. George street, Room 1207
  • Lecture slides will now be posted before each class
  • TA help sessions will be announced on Quercus
  • You are required to be in class to participate in the Poll Everywhere questions. Participating from outside of class is an academic offense
    • So is asking someone to answer for you

Observing Project Options

  1. Rotation of the Sun
  2. Photograph the Moon at different Phases: Photograph the moon at different phases to track the moon cycle

Recap - Asteroid Belt

  • Many thousands or millions of “rubble piles”
  • Material left over from the formation of the solar system, prevented from turning into a planet by tides from Jupiter
  • Much lower density than portrayed in movies - roughly 1 asteroid per million square kilometers
    • You would have to aim at an asteroid to hit it if you travelled through the belt

The Kuiper Belt

  • Vast collection of small Icy bodies beyond the orbit of Neptune
  • Includes several of the Dwarf Planets, including Pluto
  • Total mass around that of the Earth’s moon
  • Two objects visited by the New Horizons probe (NASA)

Arrokoth

  • Kuiper Belt object visited by the New Horizons probe in 2019
  • 36 × 20 × 10 km in size
  • 6 light-hours from Earth!

Comets

  • Smaller icy bodies from the outer solar system
  • Highly elliptical orbits
  • Emit tails when they get close to the sun

Voyagers 1 and 2

  • Twin spacecraft launched in 1977 to study the outer solar system and interstellar space
  • Both spacecraft are still taking data to this day, but are expected to run out of power between 2025-2036
  • Both spacecraft have entered interstellar space as of 2012
  • Both spacecraft carry the Golden Records - a time capsule of humanity intended to communicate a story of our world to extraterrestrials

Activity

Simple and surprising activity to learn about the distances in the solar system.

  • Cut out a piece of paper tape – about 1m long. Write “Sun” at one end and “Pluto – Kuiper Belt” at the other end.
  • Fold the paper in half - Write Uranus in the middle
  • Fold the second half in two (Uranus and Pluto) - write Neptune
  • Same to the first half - write Saturn
  • Halfway between Sun and Saturn - Jupiter
  • Halfway between Sun and Jupiter - asteroid belt
  • Halfway between the Sun and the asteroid belt - Mars
  • In between the Sun and Mars, draw 3 lines and label them Mercury, Venus, Earth

Scale Model

  • Sun: grapefruit
  • Mercury: grain of salt
  • Venus: mustard seed
  • Earth: mustard seed
  • Moon: grain of salt
  • Mars: poppy seed
  • Jupiter: hazelnut
  • Saturn: peanut
  • Uranus: popcorn kernel
  • Neptune: popcorn kernel
  • Kuiper Belt Object: grain of salt
  • Oort Cloud Object: grain of salt

Summary

  • How can we describe the shape and motion of objects in the solar system?
    • Except comets, most objects have near circular elliptical orbits and are often rotating
  • How are the patterns of motion in the solar system related to how it is formed?
    • Most objects orbit and rotate in the same direction
  • What is the difference between a terrestrial and a Jovian planet?
    • Distance from Sun, chemical composition, size, mass

Learning Goals

At the end of the lesson, students should be able to:

  • Explain the concept of angles
  • Describe what the Universe looks like from the Earth
  • Explain why stars rise and set
  • Explain why the constellations we see depend on latitude and time of year
  • Explain what causes the seasons
  • Explain how the orientation of the Earth’s axis change with time?

Angles

Angles are measured in degrees (symbol = °)

What is a constellation?

A constellation it's a group of stars that looks like a particular shape in the sky and has been given a name. These stars are far away from Earth. They are not connected to each other at all. Some stars in a constellation might be close while others are very far away.

Declination

88 Modern IAU Constellations - Based on Greek constellations

The Celestial Sphere

  • The North Celestial pole is the point directly over Earth’s North Pole
  • The South Celestial pole is the point directly over Earth’s South Pole
  • The Celestial equator is the projection of Earth's equator into space
  • The Ecliptic is the path the Sun (and planets) follows as it appears to circle around the celestial sphere once each year

Motions in the Sky

Two major kinds motion in the sky are evident:

  • Diurnal (Daily) Motion: The Sun, Moon, and Stars move overhead from east to west. This motion is due to the rotation of the Earth on its axis.
  • Orbital (Annual) Motion: The Sky changes while looking at the same location every night. It repeats itself (more or less) once each year. This motion is due to the orbit of the Earth around the Sun

The Ecliptic

  • The Ecliptic is the plane of our solar system
    • If you want to find planets, that is where they are
  • There is a series of constellations along the ecliptic
    • These constellations are the zodiacal constellations
    • This is where astrology comes from
  • The Ecliptic IS NOT the Celestial Equator!
    • This is due to the tilt of our planet

Zodiac

As the Sun moves along the Ecliptic as seen from Earth, it passes through 12 ancient constellations known as the Zodiac.

Solstice

Solstices are the days when the Earth is tilted most toward or most away from the Sun - define the longest and shortest day

Equinox

Two points in Earth’s orbit where day and night are equal. Earth’s axis is not pointed toward or away from the sun.

Astronomy vs Astrology

  • Astronomy is the science of studying stars, galaxies, and everything in space to understand how the universe works and our place in it. It relies on evidence and the scientific method.
  • Astrology, on the other hand, is a belief system that links the positions of stars and planets to human traits or events. It’s not based on scientific evidence, though it holds cultural meaning for many people.

Summary

  • What does the Universe look like from Earth?
    • ~4000 visible stars plus the glow of billions more
    • Often visualized as constellations in the sky
  • Why do stars rise and set?
    • Rotation of the Earth
  • Why do the constellations we see depend on latitude and time of year?
    • Visible region of sky at night changes as we orbit the Sun
    • Latitude sets what portion of celestial sphere is visible
  • What causes the seasons?
    • Tilt of rotation axis

Learning Goals

  • What is the physical configuration that leads to a particular phase of the moon?
  • What is the difference between a lunar and a solar eclipse?
  • Why don’t we see eclipses every month?
  • When will the moon rise/set tonight (assuming I know the phase of the moon?)

Moon phases

The moon doesn’t look like a round ball all the time. It changes

Moon Phases

  • New Moon
  • Crescent Moon
  • First Quarter Moon
  • Gibbous Moon
  • Full Moon
  • Last Quarter Moon

New Moon

  • When the moon is in the direction of the sun.
  • The only time a Solar eclipse can happen.
  • Unlit side faces the Earth.
  • Rises with the sun and sets with the sun.
  • Not generally visible.

Waxing Crescent

  • 3-4 days after the new moon.
  • Rises around 3 hours after the sun.
  • Sets around 3 hours after the sun.
  • Easiest to see right after sunset.

Waxing (First) Quarter

  • 1 week after the new moon.
  • Moon is lit from the side.
  • Rises around 6 hours after the sun.
  • Sets around 6 hours after the sun.
  • Easiest to see at night before midnight.

Waxing Gibbous

  • 10 - 11 days after the new moon.
  • Rises around 9 hours after the sun.
  • Sets around 9 hours after the sun.
  • Easiest to see at night – but may set before sunrise.

Full Moon

  • Two weeks after the new moon.
  • The only time a Lunar eclipse can happen.
  • Rises around 12 hours after the sun rises.
  • Sets around 12 hours after the sun sets.
  • Visible most of the night

Waning Gibbous

  • 10-11 days before the next new moon.
  • Rises around 3 hours after the sun sets.
  • Sets around 3 hours after the sun rises.
  • Rises before midnight, and is up the rest of the night and morning.

Waning (Third) Quarter

  • Around a week before the next new moon.
  • Rises around 6 hours before the sun rises.
  • Sets around 6 hours before the sun sets.
  • Rises around midnight, and is up the rest of the night and morning.

Waning Crescent

  • 2-4 days before the next new moon
  • Rises around 3 hours before the sun rises.
  • Sets around 3 hours before the sun sets.
  • Easiest to see before sunrise.

Eclipses

Eclipses occur when:

  • The Moon crosses the ecliptic
  • The Earth, Moon, and Sun align
  • The Moon casts a shadow on the Earth
  • Or, the Earth casts a shadow on the Moon

Solar Eclipse

  • When the Moon blocks light from the sun.
  • Happens when the New Moon crosses the ecliptic plane.
  • Because the Moon’s orbit is tipped relative to the ecliptic plane, this happens rarely (every few years, somewhere on earth.)
  • It only casts a shadow on a small part of the Earth

Total Solar Eclipse

A total solar eclipse occurs when the Moon is closer to Earth and blocks out all of the Sun for a portion of its shadow.

Angular Size

The angular size of an object on our sky depends on two factors:

  1. The physical size of the object
  2. How far away it is from us

Annular Solar Eclipse

  • Happens when the moon is at or near its farthest point from Earth.
  • Because the Moon is farther away from Earth, it appears smaller than the Sun and does not completely cover the Sun.
  • As a result, the Moon appears as a dark disk on top of a larger, bright disk, creating what looks like a ring around the Moon.

Annular vs Total Solar eclipses

Moon is farther away from earth so slightly smaller. Doesn’t completely cover the Sun. A ring of sunlight is visible around the moon.

Moon is similar in size with the Sun. Completely covers the Sun. Only the solar corona is visible.

Perigee

Closest to the Earth
356,355 km356,355 \text{ km}
33.5 arc-min33.5 \text{ arc-min}

Apogee

Farthest from the Earth
406,725 km406,725 \text{ km}
29.4 arc-min29.4 \text{ arc-min}

Lunar Eclipses

  • When the moon enters the Earth’s shadow
  • Happens when a full moon crosses the ecliptic plane.
  • In a full lunar eclipse, the moon is much darker and red.
    • Sometimes called a “Blood Moon”
  • The sun’s light is bent around the earth by the earth’s atmosphere, partially lighting up the moon.
  • In a partial lunar eclipse, the shadow of the earth covers part of the moon.
  • Can be seen from anywhere on earth
  • More common than a solar eclipse (the Earth is larger than the moon, so has a larger shadow).

Summary

  • What is the physical configuration that leads to a particular phase of the moon?
    • Note the different ways that the Sun illuminates Earth-Moon system
  • What is the difference between a lunar and a solar eclipse?
    • Solar: Moon blocks sunlight from reaching Earth
    • Lunar: Earth blocks sunlight from reaching Moon
  • Why don’t we see eclipses every month?
    • Moon’s orbit is inclined relative to Earth’s orbit around the Sun
  • When will the moon rise/set tonight (assuming I know the phase of the moon?)
    • See the next slide ;)

Moon Phases over a 29.5 day cycle:

Waxing Phases

  • Visible in the afternoon and evening
  • Light increases across the face each day, rises later each day
    Waning Phases
  • Visible in the late night and morning
  • Light decreases across the face each day, sets later each day