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Skydome 2015

The skydome is coming to the school on Wednesday 16th December 2015. This year we are offering second year students the chance to attend a 50 minute show in the Assembly Hall in the portable planetarium at some time during the day. The cost is €5.50. Students must pay online by going to Parents > Payments in the menus above and choosing Skydome. The strict deadline for payment is 1st December. For more information on the Skydome see

Introduction to Astronomy

Solar Eclipse 2015
January 2014 Stargazing
Basics of Astronomy
Solar System
Star Cluster
Planets Easily Seen
Ecliptic and Motion of Planets in the Sky
Life cycle of a star
Physics for Astronomy



Astronomy is an extra-curricular activity which is touched on in many subject areas in school, most notably in physics, geography, chemistry, art, maths etc. Quite a few aspects are discussed in physics.

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Solar Eclipse 2015

DO NOT STARE AT THE SUN with the naked eye, or with sunglasses, especially not through telescopes or binoculars, even during a total eclipse during peak darkness. You can go blind whilie feeling no pain like Galileo did. Only through special solar eclipse glasses can you safely look directly at the sun.

A solar eclipse is where the sun is eclipsed (blocked out) by the moon getting in the way between the earth and the sun. An eclipse can be partial or complete. On Friday the 20th March 2015, on the spring equinox, there will be a 90% eclipse visible from Drogheda, between about 8:30 am and 10:30 am with peak darkness at around 9:30 am. We can expect darkness. It will go very quiet. The birds will go quiet and the wind will die down. If the sky is clear we may see a chunk missing from the sun with only a crescent remaining, a bit like a new moon only wider.

In Greenhills we will have a few binoculars set up to project a small image of the sun on a screen which you can look at. You may see sunspots. We will also have a number of pinhole cameras ready (cards with pin holes in them), to project a very small image on a white card at arms length. See second link below. We will also have a bucket of water to view the sun`s reflection, which you may look at but not stare at. We will also have a few converging mirrors to project an image on a screen.

If you want to try to see the eclipse outside the school that morning, weather permitting, please see Mr. Loughran at 10:40 am on Thursday 19th outside the staff room to get your name on the list. You then need your teacher`s permission to miss class for a short time (10 to 20 mins). Bring warm clothes and a white card if possible. Volunteeers will be needed for the whole first period and some of the second period to help supervise. We will probably be outside the back door from the first set of stairs between the photocopying roon and Virgo Potens on Friday morning from early on for anyone who wants a look before school begins. Even if the weather is bad it is unlikely to be overcast for the full two hours from the start to the end of the eclipse.

Daily Mirror/Astronomy Ireland Guide to the Eclipse in Ireland 2015

How to safely view the eclipse

How to make a shoe box pinhole camera to safely view the eclipse

RTE have a 3 minute simulation of what the eclipse may look like from Dublin

Live streaming video of the eclipse from Trinity College Dublin School of Physics

Live streaming video of the eclipse from the Faroe Islands

Thanks Ms. Brennan!

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January 2014 Stargazing

On 15th January 2014 there was a talk on astronomy in the physics lab, lab 3, at 4 pm and at around 5 pm we went outside to look at the stars.

What to wear and bring

The main thing to bring is warm clothes. In the winter if the sky is clear it gets very cold, especially if you are standing around looking through a telescope or binoculars. Wear warm vests, multiple layers, coats, tracksuit bottoms over tights, good shoes, a wooly hat, gloves and scarf.

If you have a telescope, binoculars, books or magazines please bring them. You may leave them in the lab for a while if you wish and they will be safe.

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Basics of Astronomy


Solar system

The solar system is the Sun and planets and other objects which orbit the Sun like dwarf planets, asteroids (most in the asteroid belt) and comets.

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Our nearest star. A ball of plasma (superheated gas), made of 75% hydrogen and 25% helium and traces of other elements. Nuclear fusion takes place in the core at a temperature of around 1010 K (kelvins, like degrees centigrade). The surface temperature is only 5770 K, which is why the peak radiation from the sun is given out as visible light. (The sun also emits radio waves, microwaves, infra red, (visible light), ultraviolet light and x-rays. All these are called Electromagnetic Radiation – see Spectrum below.) Sunspots are areas of intense magnetic fields with eruptions which traverse the sun over an 11 day period as the sun rotates. They cause the emission of cosmic rays, high speed charged particles including protons, which cause the Aurora and interfere with communications satellites.


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“My Very Easy Method Just Sums Up Nine Planets” –  Frank Mooney.


Distance from sun, in AU, Astronomical Units.

*1 AU is distance of earth from sun.

1 AU = 1.5 x 1011 m = 150 000 000 000 m = 150 000 000 km = 93 000 000 miles



Explanation: Scientific Notation

[Scientific notation is a handy way of writing down astronomical numbers.]

*Distance of earth from sun is 1 AU (Astronomical Unit).

*1 AU = 1.5 x 1011 m (= 150 000 000 000 m = 150 000 000 km = 93 000 000 miles)

[1.5 x 1011 means 150 000 000 000 (1.5 with 11 noughts added on to 1, move decimal point 11 places to the right)

6.7 x 10-11 means 0.000 000 000 067 (move decimal point 11 places to the left)]

[On the calculator press 1.5 Exp 11 and you will see 1.5 x 1011 on the display.

On the calculator press 6.7 Exp +/- 11 and you will see 6.7 x 10-11 on the display.

Instead of Exp, your calculator may use a x10x button so you press 1.5 x10x11]





Relative size



H: Google solar system, two planets (compare re

Planet Venus Earth Mars Jupiter Saturn
Relative Size (diameter) 0.95 1 (12 800 km)


(6 400 km)


(142 984 km)

Relative Mass (relative to earth) 0.80 1 (6 x 1024 kg) 0.1 (6 x 1023 kg) 11 6
Distance from sun 0.72 1 AU
(150 000 000 km)

1.5  AU

(230 000 000 km)

5.2 AU 6 AU
Orbital period 0.60 1 y 1.9 y 12y 29 y
Rotational period 243 d 1 d 1.05 d 10 h 10 h
Composition rocky rocky rocky gas giant gas giant
Atmosphere   N,O,He CO2, N, Ar    
Satellites and rings   1 (Moon)

2 moons

(Deimos, Phobos)

Other interesting facts

Pressure =

100 atm

Pressure =

      1 atm

Pressure = atm    

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Stars are like our sun mostly, only farther away; balls of gas mostly made of hydrogen and helium.

Fusion in their cores give out energy which leaves the surface as light and other forms of radiation.

Explanation: Light year

A light year is the distance light travels in one earth year, about 1013 km.

The speed of light is 3.0 x 108 m s-1 (metres per second)

Q: How far can light travel in a year?

A:  1 y = 365.25 d = 365.25 x 24 h = … = 365.25 x 24 x 60 x 60 s = 3.157 x 107 s.

So there are about 3.2 x 107 seconds in a year.

Since light travels 3.0 x 108 metres per second then one light year is

1 ly = 3.0 x 108 m s-1 x 3.157 x 107 s =  9.471 x 1015  m 

So 1 ly is approximately = 1016 m = 1013 km = 10 000 000 000 000 km.

It takes about 8 minutes for light from the sun to reach us, so the Sun is 8 light minutes distant.

The moon is only 380 000 km away, or about 1.3 light seconds distant.

The nearest star to us, Proxima Centauri, is about 4 ly away.

Many stars we see are about 100 ly away. This means that we are seeing them as they were, 100 years ago. Some of them may no longer be there!

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Star cluster





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A nebula is a fuzzy patch unlike a star which is a bright point. A nebula could be a galaxy, a cloud of dust and or gas e.g. the Orion nebula, a dust cloud lit up by stars to which it is giving birth.

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A constellation is a visible pattern of stars in the night sky which may or may not be close to each other.




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Planets Easily Seen

Jupiter and its 4 Gallilean satellites: Io, Europa, Ganymede and Callisto (3 of Zeus’s lovers and Ganymede – a male beauty).



Other planets visible with the naked eye:

Venus: “Morning Star” – very bright and low in the East in the morning just before/after sunrise or

“Evening Star” – very bright and low in the West just before/after sunset.

Mercury – not as bright, lower down in same position as Venus, harder to spot.

Mars – “Red Planet”, along the Ecliptic, in Jan 2014 visible in the East from midnight to sunrise.

Saturn – with its rings, only visible early in the morning before sunrise in the East in Jan 2014.

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The Ecliptic and Motion of Planets in the Sky

The Ecliptic is an imaginary line we draw across the sky to trace the path of the Sun from where it rises in the East to where it sets in the West. Everything (Sun, Moon, stars, planets move from left to right (East to West) as the night progresses, due to the Earth’s rotation.

All the planets follow this line fairly closely as does the Moon though the Moon can be a little above or below the ecliptic as its orbit is 7 degrees out of line with the Earth’s orbit around the Sun.

As the month progresses the Moon moves from right to left along the ecliptic, about 1/28 th of a revolution every night. The moon is in the same position every 28 or 29 days, a month (Moonth).

As the year goes by the planets move from right to left along the ecliptic. The inner planets move faster while the outer planets move slower.  Jupiter takes 11 years to orbit the Sun so it completes about 1/11 th of a circle in one year. In January 2014 Jupiter was in the constellation Gemini as shown but it will move further left (East) as the months pass.

The word “Planet” means wandering star since the planets seem to wander among the fixed stars.

The sky in the East around 6 pm on 15/1/2014:-


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Life cycle of a star


  1. Birth – protostar – clouds of gas and dust attracted by gravity
  2. Main sequence – star – nuclear reactions produce energy, light, star shines (Sun)
  3. Death – fuel (hydrogen) runs out – star collapses
    1. Small star -> white dwarf – small still visible star
    2. Medium sized star -> red giant then white dwarf
    3. Large star (3 to 8 solar masses) -> red supergiant then neutron star
    4. Very large star (>8 solar masses) -> red supergiant then black hole

In the red giant phase, outer envelope of star swells up

(our sun will envelop Mercury, Venus & maybe Earth),

the envelope gets blown away and a dwarf is left behind in centre.

Supernova: when a star explodes, in its dying phase, extremely bright due to high energy nuclear reactions which produce heavy elements (like those in our body).

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A lump of ice or rock which comes from the remains of the tail of a comet which the earth’s orbit is crossing. When a meteor hits the earth’s atmosphere it burns up in a few seconds and is called a “shooting star”. If a meteor reaches the earth it is called a meteorite. This may cause damage or even a crater.

Sky Diary

You could keep a diary of what you observe with sketches, indicating rough location in the sky and time, including the following:-

moon phase & position on few nights orion
sun rise and sunset times, position aldebaran*
map of southern sky pleiades (7 sisters)
constellations incl. plough (bear)
  polaris* (N pole star)
Jupiter and its moons


Other topics to research / Google

Star signs


Star formation

Formation of solar system

Nuclear reactions within stars – nuclear fusion




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Physics for Astronomy




*Weight is the force of gravity acting on an object

W = mg

W = weight (force of gravity) (in N, newtons)

m = mass (in kg)

g = acceleration due to gravity (in m s-2)

g = 9.8 (or 10) m s-2 on earth

g = 1.6 m s-2 on the earth’s moon

Q: Calculate your weight in N if your mass is 60 kg (i) on earth (ii) on the moon.

A: W = mg

(i)         = 60 kg x 9.8 m s-2   = 588 N  ( 1 N = 1 kg m s-2   ) approx = 600 N

(ii)        = 60 kg x 1.6 m s-2   = 96 N  ( 1 N = 1 kg m s-2   )   approx = 100 N

[F between a human and the earth, human-moon, moon-earth, earth-sun

Newton’s law of gravitation]


Newton’s law of gravitation

force between two point masses is

proportional to the product of the masses and

inversely proportional to the square of the distance between them

image013             image014

F = gravitational force (N)

m1, m2 = masses

d = distance between masses

G = universal gravitational constant (6.67 x 10-11 N m2 kg-2)


Force of gravity on a planet’s surface

image015              image016


F = gravitational force (N);

M = mass of planet; m = mass of body

R = radius of planet

G = universal gravitational constant



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