Starry Starry Night

Science Olympiad

Universe

The Everything

The whole of all matter, energy, planets, stars, and galaxies. It includes everything we can see, and even the "empty" space in between. It is so big that it is still expanding every single day!

Big Bang Theory

A leading scientific model explaining that the universe began roughly 13.8 billion years ago and has been expanding ever since.

Key Evidence: Astronomers (like Edwin Hubble) noticed that distant galaxies are moving away from us, proving the Universe is still stretching.

Galaxy

The Cosmic City

A massive collection of billions of stars, gas, and dust held together by gravity. Our Solar System is just one tiny spot inside a galaxy called the Milky Way.

A single galaxy can hold billions of stars, planets, and giant clouds of gas called Nebulae.

Local Group

Group of Galaxies

A relatively small cluster of galaxies that are gravitationally bound together. It contains more than 50 galaxies, but the three largest are:

1. The Milky Way: Our home - a spiral galaxy.

2. Andromeda (M31): Our largest neighbor - a spiral galaxy.

3. Triangulum (M33): The third-largest spiral.

Nebula (pl. Nebulae)

The Star Nursery

A giant cloud of dust and gas (mostly hydrogen) in space. These are the "construction sites" of the universe where new stars are born!

Our own Sun and planets were born inside a nebula about 4.6 billion years ago! That cloud of gas is called the Solar Nebula.

Nebular Hypothesis

 It is the leading scientific model that explains how our Solar System formed and evolved from a giant cloud of gas and dust (Solar Nebula).

The process began approximately 4.6 billion years ago.

Gravity

The Universal Pull: An invisible force that pulls objects toward each other. Anything that has Mass (stuff) has gravity. It keeps us on the ground and keeps planets orbiting the Sun.

Scientists often imagine gravity as a heavy ball sitting on a trampoline. The ball curves the trampoline, causing smaller marbles to roll toward it. This "curving" is how gravity works in the universe!

Solar System

Our Space Home

A collection of planets, moons, asteroids, and comets that all travel around one central star - the Sun. Gravity holds everything together in this massive cosmic neighborhood.

Light Year

Definition: It is the distance that light travels in one vacuum year. Used to measure distances between stars and galaxies.

Measurement:  1 light year = 9.46 trillion kilometers (5.88 trillion miles).

Context: It's used for interstellar and intergalactic distances. For example, the nearest star to us (besides the Sun) is about 4.2 light-years away.

Time Machine Effect: Because light takes time to travel, looking at a star 10 light-years away means you are seeing it as it was 10 years ago.

Astronomical Unit (AU)

Definition: A unit of length used in astronomy, representing the average distance between the Earth and the Sun. It makes measuring vast distances within our solar system more manageable, such as stating Jupiter is about 5.2 AU from the Sun.

Measurement: 1 AU = 150 million kilometers (93 million miles).

Light Travel Time: It takes light about 8 minutes and 20 seconds to travel 1 AU from the Sun to Earth.

Quick Fact: Pluto is about 39 AU from the Sun

Star

The Giant Engine: A massive ball of super-hot, glowing gas (mostly hydrogen and helium) held together by its own gravity. Stars create their own light and heat through a process called Fusion.

The Balancing Act: A star exists because of a constant battle between two forces:

1. Gravity: Pulling everything inward toward the center.

2. Nuclear Pressure: Pushing outward from the core.

Planet

The Neighborhood Boss: A large, round object that orbits a star. To be a "major" planet, it must be big enough to have cleared its orbital path of other large debris.

Dwarf Planet

The Small Wonder: A celestial body that orbits the Sun. It is like a planet but smaller, and it hasn't "cleared its neighborhood," meaning there are still other space rocks (asteroids or ice) floating in its orbital path.

Satellite

Natural Satellites: Celestial bodies like moons orbiting planets (e.g., Earth's Moon) or planets orbiting stars (e.g., Earth orbiting the Sun).

Artificial Satellites: Machines built by humans and launched into orbit, such as the Hubble Telescope, International Space Station (ISS), or GPS satellites.

Axis

The Invisible Spinner: An imaginary straight line that runs through the center of a planet from the North Pole to the South Pole. The planet spins (rotates) around this line.

The Poles: The two points where the axis exits the planet are the North and South Poles. On Earth, the North Pole currently points toward a star called Polaris (the North Star).

Axial Tilt

Definition: The angle between a planet's rotational axis (the imaginary line it spins around) and its orbital path around the Sun.

The Cause of Seasons: Earth’s axial tilt is the only reason we have seasons. As we orbit the Sun, different parts of the Earth lean toward the Sun at different times of the year.

Earth's Tilt: Exactly 23.5°.

The Extremes:

1. Venus: Nearly upside down (177^o), causing retrograde rotation.

2. Uranus: Tilted totally on its side (98^o), causing sideways rotation.

Orbit

The Endless Fall: A regular, repeating path that one object in space takes around another.

Orbit Facts

• Ellipse: Most orbits aren't perfect circles; they are slightly oval-shaped, called an ellipse.

• Orbital Period: The time it takes to complete one full trip around a Star.

• Orbital Velocity: The specific speed needed to stay in orbit. If you go too slow, you crash; if you go too fast, you fly away!

Ellipse

The Oval Path: A geometric shape that looks like a flattened or "stretched out" circle. In space, most orbits (planets, moons, and comets) follow this shape rather than a perfect circle.

Eccentricity

The Stretch Scale: A measurement of how much an orbit deviates from a perfect circle. It is a number between 0 and 1. The closer the number is to 1, the more "stretched out" or "squashed" the orbit looks.

Perturb / Perturbation

• Simple Definition: To knock an object off its regular orbital path using gravity.

• The Cause: Gravity from a large, nearby object (like a planet or a star).

• Example: Neptune was discovered because astronomers noticed Uranus’s orbit was being perturbed (pulled slightly) by an invisible gravity source nearby!

Rotation

The Big Spin: The spinning of a planet or moon on its imaginary internal line called an axis. One full rotation equals one day for that planet.

Prograde Rotation

Definition: The "forward" or "standard" rotation of a planet. It means the planet rotates in the same direction that it orbits the Sun.

The Direction: When viewed from above the Sun's North Pole, prograde rotation is counter-clockwise.

The "Sun Rule": On a prograde planet, the Sun rises in the East and sets in the West.

Who does it?: 6 out of the 8 planets in our Solar System have prograde rotation: Mercury, Earth, Mars, Jupiter, Saturn, and Neptune.

Why?: It follows the original "spin" of the solar nebula that created us 4.6 billion years ago.

Retrograde Rotation

Definition: The "backward" rotation of a planet. It means the planet rotates in the opposite direction that it orbits the Sun.

The Direction: When viewed from above the North Pole, retrograde rotation is clockwise.

The "Sun Rule": On a retrograde planet, the Sun rises in the West and sets in the East.

Who does it?: Venus is the most famous example (it spins very slowly backward).

Why?: Scientists believe that Venus was hit by a massive object (a perturbation!) billions of years ago that knocked its rotation completely out of whack.

Sideways Rotation

• Definition: An extreme axial tilt that makes the planet appear to be lying on its side.

• The Tilt: Uranus has an axial tilt of about 98°. For comparison, Earth’s tilt is only 23.5°.

• The Look: Uranus doesn't spin "up and down"—it rolls along its orbital path.

• The Seasons: This tilt creates extreme seasons. Each pole gets 42 years of direct sunlight followed by 42 years of total darkness!

• The Cause: Most scientists believe a giant object (the size of Earth!) crashed into Uranus long ago and knocked it over.

Revolution

The Long Journey: The movement of one object around another in space. For planets, this means traveling in an orbit around the Sun. One full revolution equals one year.

The Speed: Planets closer to the Sun have to move much faster to stay in orbit.

• Earth travels at about 67,000 miles per hour!

• Mercury (the closest) zips around at 107,000 mph.

The Time: The further a planet is from the Sun, the longer its "year" takes because it has a much longer path to travel.

Aphelion & Perihelion

These terms describe the "Far" and "Near" points of a planet's path around the Sun. These two points exist because orbits are not perfect circles; they are Ellipses (oval-shaped).

APHELION: The Far Point: This is the specific place in a planet's orbit where it is at its furthest distance from the Sun.

• Memory Trick: "A" is for "Away."

PERIHELION: The Near Point: This is the specific place in a planet's orbit where it is at its closest distance to the Sun.

• Memory Trick: "P" is for "Proximate" (Close).

Apogee & Perigee

The Orbital Extremes: Because orbits are ovals (ellipses), the distance between Earth and its satellites constantly changes.

Apogee: The point where the object is farthest away.

Perigee: The point where the object is closest.

How to Remember the Difference

• Apogee = Away (Farthest point).

• Perigee = Proximity (Closest point).

Day

A day is defined by Rotation, which is when a planet spins like a top on its invisible "axis”.

• Solar Day: The time it takes for the Sun to return to the same spot in the sky (like noon to noon). On Earth, this is 24 hours.

• Sidereal Day: The time it takes for a planet to spin exactly 360° relative to distant stars. On Earth, this is 23 hours and 56 minutes.

The Difference: Because Earth moves in its orbit while it spins, it has to turn a little bit extra each day to face the Sun again.

Month

A month is defined by the Moon's orbit around a planet. Because Earth moves around the Sun at the same time the Moon moves around Earth, we have two types of months:

• Sidereal Month: How long it takes the Moon to make one full circle (360°) around Earth. This takes 27.3 days.

• Synodic Month: How long it takes to go through all the Moon Phases (from New Moon to the next New Moon). This takes 29.5 days.

The Difference: The Moon has to travel a little further to get back into the same "phase" because Earth moved during that time.

Year

A year is defined by Revolution, which is one complete trip (orbit) around the Sun.

• Earth Year: It takes Earth 365.25 days to go around the Sun.

• The Leap Year: Since we can't have a quarter-day on our calendars, we save up those ".25" days. Every four years, they add up to one full day (0.25 x 4 = 1), which we add to the calendar as February 29th.

Other Planets: A year is different for every planet. Mercury has a short year (88 Earth days) because it is close to the Sun. Neptune has a very long year (165 Earth years) because it is so far away!

Season

The four divisions of the year (Spring, Summer, Autumn, Winter) marked by particular weather patterns and daylight hours.

Seasons are not caused by how close the Earth is to the Sun. Instead, seasons happen because of two main things working together: Earth’s Tilt and Earth’s Orbit.

Solstice

The two days of the year (around June 21 and December 21) when the Sun reaches its highest or lowest point in the sky at noon. This is when the Earth's axial tilt is leaning most directly toward or away from the Sun.

June Solstice

When: Happens every year around June 21.

It is the Summer Solstice (longest day) in the Northern Hemisphere while Winter Solstice (shortest day) in the Southern Hemisphere

December Solstice (or Winter Solstice)

When: Happens every year around December 21.

It is the Winter Solstice (shortest day) in the Northern Hemisphere while Summer Solstice (longest day) in the Southern Hemisphere

Equinox

An equinox occurs twice a year (around March 21 and September 23) when the Earth's axis tilts neither toward nor away from the Sun, resulting in nearly equal amounts of daylight and darkness everywhere on Earth. It signifies the sun being directly over the equator, marking the first day of spring or autumn.

Vernal Equinox

When: Happens every year around March 21.

It is the Spring Equinox (1^st day of Spring) in the Northern Hemisphere while Fall Equinox (1^st day of Fall) in the Southern Hemisphere

Autumnal Equinox

When: Happens every year around September 21.

It is the Fall Equinox (1^st day of Fall) in the Northern Hemisphere while Spring Equinox (1^st day of Spring) in the Southern Hemisphere

Moon Phases

Moon phases are the different ways the Moon looks from Earth as it orbits us. The most important thing to know is that the Moon does not actually change shape. It also doesn't make its own light; it acts like a giant mirror reflecting light from the Sun.

New Moon

• What is it? The phase where the Moon is positioned between the Earth and the Sun.

• What do we see? From Earth, the Moon looks completely dark. We can't see it because the side being lit up by the Sun is facing away from us.

• The Start of the Cycle: This is "Day 0" or "Day 1" of the lunar month. In about 29.5 days, we will have another New Moon.

Waxing Crescent

• What does "Waxing" mean? It means the illuminated (lit up) part of the Moon is growing or getting larger each night.

• What does "Crescent" mean? The Moon looks like a thin curved sliver, similar to a banana or a fingernail.

• What do we see? A tiny sliver of light on the right side (in the Northern Hemisphere).

• When does it happen? A few days after the New Moon. It usually appears low in the western sky right after sunset.

First Quarter

• What is it? The phase where the Moon has completed one-quarter ($25\%$) of its orbit around the Earth.

• What do we see? Exactly half of the Moon’s face is illuminated. It looks like a "D".

• The "Right" Rule: In the Northern Hemisphere, the right side is lit up, and the left side is dark.

• Timing: It occurs about one week after the New Moon. It rises around noon and is high in the sky at sunset.

Waxing Gibbous

• What does "Gibbous" mean? It comes from a Latin word meaning "humpbacked." It describes a shape that is larger than a semi-circle but smaller than a full circle.

• What does "Waxing" mean? The light is still growing.

• What do we see? Most of the Moon is lit up on the right side, with only a small "sliver" of darkness left on the left.

• Timing: This phase happens during the week leading up to the Full Moon. You can often see this moon in the late afternoon before the sun even sets!

Full Moon

• What is it? The phase where the Earth is positioned roughly between the Sun and the Moon.

• What do we see? The entire side of the Moon facing Earth is fully lit up. It looks like a perfect, bright circle.

• Timing: This happens about 14 days (two weeks) after the New Moon.

• The Schedule: A Full Moon rises almost exactly at sunset, stays up all night, and sets at sunrise.

Waning Gibbous

• What does "Waning" mean? It means the illuminated (lit up) part of the Moon is shrinking or getting smaller each night.

• What does "Gibbous" mean? The Moon is still more than half-lit, but it is no longer a perfect circle.

• What do we see? Most of the Moon is lit up, but now the shadow is starting to creep in from the right side. This means the light is now on the left side (in the Northern Hemisphere).

• Timing: It happens a few days after the Full Moon. It rises later and later in the evening, often staying visible in the western sky after the sun comes up in the morning!

Third (Last) Quarter

• What is it? The phase where the Moon has completed three-quarters ($75\%$) of its orbit around the Earth.

• What do we see? Exactly half of the Moon is lit, but it is the opposite side of the First Quarter. It looks like a "C" or a backwards "D".

• The "Left" Rule: In the Northern Hemisphere, the left side is lit up, and the right side is dark.

• Timing: It happens about three weeks after the New Moon. It rises around midnight and is high in the sky at sunrise!

Waning Crescent

• What is it? The final "sliver" of light before the Moon becomes invisible again.

• What does "Waning" mean? The light is shrinking (getting smaller).

• What do we see? A thin, curved sliver of light on the left side (in the Northern Hemisphere).

• Timing: This happens just a few days before the New Moon. It rises in the very early morning (before dawn) and sets in the afternoon.

Eclipse

An eclipse happens when one object in space blocks another object from view, or when one object casts a shadow on another.

In our solar system, this usually involves the Sun, Earth, and Moon lining up perfectly. There are two main types you need to know: Solar and Lunar.

Solar Eclipse

A solar eclipse happens during the New Moon phase. The Moon passes directly between the Earth and the Sun, blocking the Sun’s light and casting a shadow on Earth.

• What you see: For a few minutes, the sky gets dark in the middle of the day, and you can see the Sun’s outer atmosphere (the corona).

The Order: Sun → Moon → Earth.

Lunar Eclipse

A lunar eclipse happens during the Full Moon phase. The Earth passes directly between the Sun and the Moon. The Earth blocks the sunlight from hitting the Moon, and the Moon moves into Earth’s shadow.

• What you see: The Moon doesn't go completely black; it usually turns a deep red color. This is because Earth's atmosphere bends a little bit of red light onto the Moon (this is sometimes called a "Blood Moon").

The Order: Sun → Earth → Moon.