SPU set 3

What is a solar eclipse?
A solar eclipse occurs when the moon is directly between the Earth and the Sun

What is a lunar eclipse?
A lunar eclipse occurs when the Earth is between the Sun and the Moon. The Moon is completely darkened when it enters the darkest part of the Earth’s shadow (umbra) and there is a partial lunar eclipse when it is in the penumbra.

Umbra en penumbra?
Umbra = kernschaduw, darkest part of a shadow
Penumbra = halfschaduw, the less dark part of a shadow

What are total eclipse, and annular eclipses?
When the Moon is close enough to the Earth, it will cover the Sun completely; this is a total solar eclipse. When the moon is further away from the Earth, then its disk will not be big enough to cover the Sun completely, and we get an annular solar eclipse.

Chapter 3: The moon
What are the basic characteristics of the moon?
- It reflects light, that’s why we can see it.
- The moon is much smaller than the earth
- The surface of the moon is smaller than Africa
- It also weighs less than the earth, due to the gravitational force is less strong.
- The moon has no atmosphere due to lack of gravitational force
- It takes the moon 27.3 days to circle around the earth
- The moon cannot “escape from the Earth” due to the gravitational force of the Earth 

Why is there ebb & flow? And why twice a day?
Twice per 24 hours there is ebb and flow. The coming up and moving away from the water follows the regularity of the clock. The reason we have ebb and flow is because of the gravitational pull of the moon and also slightly by the sun. The constant orbit the moon around the Earth causes a permanent gravitational pull. The moon actually pulls the water of the Earth towards itself; flow occurs at the place that faces the moon, also on the opposite side flow occurs. This is causes because the Earth on its own is also pulled towards the moon. Because the Earth turns around its own axis in 24 hours, it’s ebb and flow twice a day.

Why do the different phases of the moon exist?
The phases of the Moon are produced by the alignment of the Moon and the Sun in the sky.

What is neap tide? And what is spring tide?
The sun is much further than away that the moon, and also much heavier. The sun also has an influence on the tides. When the sun and the moon are in one line, we call it spring tide. When the moon is in first or last quarter, we call it neap tide.

Why is it always the same side of the moon we see?
The reason that one side of the Moon is never visible from the Earth is because the moon spins once on its axis in precisely the same amount of time it takes to revolve around the Earth.

Chapter 4: The Sun
What are the basic characteristics of the Sun?
- The Sun is the most prominent feature in our solar system, it is the largest object and contains approximately 98% of the total solar system mass
- The Earth could fit 1,3 times into the Earth
- The temperature of the Sun’s outer layer is 6,000 degrees

The equation E=mc2
The formula expresses the equivalence of energy and mass. By this formula adding energy also increases mass (both weight and inertia), removing energy decreases it.

How is solar energy created?
Solar energy is created deep within the core of the Sun. It is here that the temperature and pressure is so intense that nuclear reactions take place. This reaction causes four protons or hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. The alpha particle is about 0,7% less massive than the four protons. The difference in mass is expelled as energy and as light and heat. Energy generated in the Sun’s core takes a million years to reach its surface.

What are sunspots? What are the characteristics of sunspots?
Sunspots are regions on the solar surface that appear dark because they are cooler than the surrounding photosphere, about 1500K (thus they are still at a temperature of about 4500K). They are only dark in a relative sense; a sunspot removed from the bright background of the sun would glow brightly.

Chapter 5: The Solar System
What are the eight different planets in the correct order?
Maak Van Een Mooie Japanse Stof Uw Nieuwe Pyjama
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto

What is a dwarf planet?
Dwarf planets are a category of solar system bodies created by the International Astronomical Union in 2006 to describe objects orbiting the Sun that are big and heavy enough to resemble a planet, but not big enough to 'clear' a free path on its orbit.

What is the difference between an inner and an outer solar system?
After Mercury, Venus Earth and Mars there is the asteroid belt, this divides these two ‘solar systems’. Also, the first 4 planets are terrestrial planets as they mainly consist of rock and metal. The outer four planets Jupiter, Saturn, Uranus and Neptune are gas giants (jovian planets), consisting of largely of hydrogen and helium and have a larger mass.

Who was Ptolemy and what was his World view?
He created the geocentric model, or the Ptolemaic worldview of the universe; this model is where Earth is the centre of the universe and other objects go around it. Belief in this system was common in ancient Greece, it was embraced by both Aristotle and Ptolemy; he developed this model in the second century after Christ.

Who was Copernicus and what was his world view?
In 1543 the geocentric system met its first serious challenge with the publication of Copernicus’ ‘De revolutionibus orbium coelestium’ which posited that the Earth and the other planets instead revolved around the sun (heliocentric) only in his model, planets made perfect circles.

Who was Tycho Brahe and was his world view?
The Tychonic model was published by Tycho Brahe in the late 16th century. It combined what he saw as the mathematical benefits of the Copernican system with the philosophical and “physical” benefits of the Ptolemaic system. Tycho Brahe never became a famous scientist, although he has done some important discoveries. In the end Galileo Galilei proved that there should be a heliocentric world view.

Geocentric = Where everything revolves the Earth, Heliocentric is where everything revolves around the Sun.

What is an Astronomical unit?
Distances in the universe are enormous. The distance between sun and earth is about 150 billion kilometres. We call the average distance between the Sun and the Earth astronomical unit or AU. 1 AU is about 1.469 x 1011

What is a light year?
The velocity of light is 300.00 km in one second, you can now calculate the distance travels in one year; this is what we call a light year (9,463 milliard km) Faster than light is impossible!! 

What are the laws of Kepler?
- Kepler’s First law: the orbits of the planets are ellipses; with the fun at one focus of the ellipse.
- Kepler’s Second Law: The line joining the planet to the Sun sweeps out equal areas in equal time as the planet travels around the ellipse. When you’re further away from the sun, you go slower.
- Kepler’s Third Law: The time it takes for each planet to orbit the sun (T) is related to its average distance from the sun (R)

What is the epicycle theory?
When Ptolemy observed the planets in the sky he realized that the movement of the planets could not be explained by the geocentric model: planets actually appeared to move backwards (retrograde movement) this apparent retro gradation puzzled ancient astronomers, and was one reason why they named these bodies planets, planet comes from the Greek word wanderer.

Ptolemy proposed the existence of epicycles and deferents. In the Ptolemaic system deferents were large circles around the Earth, and epicycles were small circles whose centres moved around the circumferences of the deferents the planets moved around the circumference of their own epicycles.

What are the retrograde movements of planets?
Astronomers now know that the earth completes its orbit in a shorter period of time than the planets outside its orbit. As a result, earth periodically overtakes the outer planets, like a faster car on a multi lane highway. When this occurs, the planet earth is passing will first appear to stop its eastward drift and then drift back towards the west. Then, as Earth swings past the planet in its orbit it appears to resume its normal motion west to east. The inner planets Venus and Mercury appear to move in retrograde in a similar mechanism.

Chapter 6: Stars
What are the differences between a star and a planet?
The basic difference between a star and a planet is that a star emits light produced by a nuclear reaction in its core, whereas a planet only shines by reflected light. Not all objects in the universe that don't produce their own light are planets however. Stars are big, hot balls of plasma. Planets are not as hot as stars are. Planets all orbit the sun; the planet earth orbits the sun in exactly one year.

What are equatorial coordinates?
The stars can be imagined to be points of light on a sphere which rotates about the Earth. Projecting the Earth’s poles and equator out onto this imaginary sphere provides a framework for celestial measurement.

Right ascension and declination are like longitude and latitude on the surface of the Earth except that they are measured with respect to the celestial sphere.

Right ascension is a celestial longitude measured in the direction of the Earth’s rotation. Since that rotation makes a complete circle in 24, the notation adopted for right ascension was in terms of hours and minutes with 24 hours representing the full circle. Declination is expressed as an angle with respect to the celestial equator.

For example, the celestial coordinates of the star Betelgeuse in the constellation Orion are right ascension 5 hours and 52 minutes and the declination is 7 degrees and 24 minutes(!?). A declination south of the celestial equator is given a negative sign.

What is Polaris?
This is the only star in the sky that does not turn. Polaris is very distant from Earth and located in position very near Earth’s north celestial pole.

How to find Polaris?
If you continue the line of our axis straight up, you will find Polaris somewhere near that line. Polaris is also part of the constellation Ursa Minor

What are circumpolar stars?
Stars close to the celestial poles, have a very small circle of spin. The farther from the celestial pole, the wider the circle. Stars that make a full circle around a celestial pole like Big and Little Dipper in the northern hemisphere are called circumpolar stars. They travel across the night sky and do not set. At the equator however there are no circumpolar stars because the celestial poles are located at the horizon. All stars observed at the equator rise in the east and set in the west.

What is Ursa Major? What is Big Dipper? (+ difference)
Big dipper consists of 7 bright stars that form a small bowl with a long handle. They are part of the Ursa Major. So they are NOT the same.

What is Ursa Major? What is Big Dipper? (+ difference)
Big dipper consists of 7 bright stars that form a small bowl with a long handle. They are part of the Ursa Major. So they are NOT the same.

What is Ursa Minor? What is Little Dipper? (+difference)
Little Dipper also consists of 7 stars and forms a small bowl. The Little Dipper is also part of Ursa Minor, and again NOT the same.

How to find the Little Dipper & the Big Dipper
You can find Big Dipper easily during every bright night here in the Netherlands. You can use it to find Polaris, which is again part of the Little Dipper. See chapter 2.

What is Orion? How can you find Orion?
Orion is often referred to as The Hunter, this constellation is located on the celestial equator and visible throughout the world. It includes the belt of Orion; three bright stars in a row. Surrounding the belt at roughly similar distances are four right stars which are considered to represent the outline of the hunter’s body.

What is the Southern cross? How can you find the Southern cross?
Crux (another word for Southern cross) is the smallest of 88 modern constellations, but it is one of the most distinctive. Crux is Latin for cross which is the shape of this constellation. It is easily visible from the southern hemisphere as Polaris has in the Northern Hemisphere. The vertical part of the cross points towards the South Pole.

What is Zodiac?
The Zodiac constellations were ascribed specific patterns that resemble the shapes of animals, half-animals and human beings. The Constellations of the Zodiac actually come from an imaginary belt in the sky that extends about eight degrees above and below the Plane of the Ecliptic.

Why can’t we see our own zodiac constellation on our birthday?
Because at that very moment, the sun is between Earth and that specific constellation.

What is the difference between astronomy and astrology?
Astronomy is simply the observation and measurement of celestial bodies, while astrology is an attempt to find some sort of “meaning”  or “influence” in the planetary positions.

What is the asteroid belt?
The asteroid belt is the region of the solar system located roughly between the orbits of the planets Jupiter and mars. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets

What is a meteorite?
A meteorite is a natural object originating in outer space that survives impact with the earth’s surface.

What is a meteor or a shooting star?
A meteor or shooting star is the common name for the visible path of a meteoroid as it enters the atmosphere. It’s a shooting star until it survives impact with the earth’s surface, then it’s called a meteorite.

What is a comet?
A comet is a relatively small icy mass in the solar system. When it’s close to the sun it displays a visible coma (a thin fuzzy temporary atmosphere) and sometimes also a  tail, both because of the effects of solar radiation and solar wind upon the nucleus of the planet.

What is a meteor shower?
A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are causes by streams of cosmic debris called meteoroids entering the earth’s atmosphere at extremely high speeds.

Life of a star
Nebula = cloud of gas, rock, dust, water; most of it forms to a star because of gravity. The rest orbits around the star and forms the planets.

Yellow star
- Star generates heat and light by nuclear fusion (hydrogen -> helium)
- Hydrogen runs out, gravity forces the core to shrink
- Star becomes hotter and the helium ashes ignite
- Star expands, now called red giant
- Helium all burnt into carbon. Core shrinks again into a hot dense ball, called a white dwarf
- Inner layers fall inward and ignite, causing the outer layers to be flung outward.

Black holes come from dead stars much bigger than the sun (a yellow star)

After the death of the star much more material is pulled together (gravity again). Much more mass is packed together in not much space. The result is a place were gravity is so high that even light can’t escape its pull = Black hole.

What is a stellar nebula?
This is when a star is “born”. See explanation above with “Nebula”

What is a supernova?
A star that explodes and becomes extremely luminous in the process