This website supports education in astronomy and space science
Right Now section
Moon and Sun, World times, Night Sky and more, one click away
Educators section
Quality information and resources for teaching Astronomy or Space Science
Students section
A treasure trove for anyone with a serious interest in Astronomy and Space Science
Access to our searchable quality Resources database

Some features on this website require cookies to be enabled (test here)

Lead Articles

Falling in Space

User Rating: 5 / 5

Star ActiveStar ActiveStar ActiveStar ActiveStar Active

A comprehensive primer on the technique of space travel, i.e. how we travel from A to B in space

An extended version of this article can be downloaded as an off-line resource in pdf-format 


Why are astronauts in the International Space Station (ISS) weightless? “Because there is no gravity up there” you often hear. “Astronauts and scientists themselves often talk about zero-gravity, don’t they?”.

weightlessness sandra magnus astronaut fruitWeightless in Space. Image credit: NASA A satellite orbit in its simplest form can be compared with uniform circular motion, like when you sling a weight around on a string. This circular motion requires a constant force towards the centre of the circle. For a satellite, including of course the ISS, gravity of the Earth provides that “centripetal” force. If there was no gravity up there, the ISS would take of in a tangential straight line and disappear into space because of Newton’s first law of motion .

So there definitely is gravity up there demonstrated by the fact that the ISS nicely continues to travel in its orbit. And this holds for any satellite, even the natural satellite we have: the Moon. She has been “up there” for at least 4 billion years.

Let us do some experiments
When a skydiver jumps out of a plane at high altitude it is advisable to have a parachute, but keep that folded up for a while. She falls down at increasing speed and experiences weightlessness. A disturbing influence here is the wind and air drag she experiences. Astronauts don’t have that of course, but otherwise the situation is quite similar.

Modify the experiment by putting the skydiver in a box and dropping the whole box out of the plane (This is a thought experiment. DON’T DO THIS AT HOME). Now the skydiver will not feel any wind and will be almost weightless inside the box. Almost, because the box itself experiences the air drag and therefore falls a little slower than the skydiver. She will feel a very slight weight force towards the bottom (in the direction of falling).

Let us now look at a thought experiment that was proposed in 1687. Isaac Newton published his Philosophiæ Naturalis Principia Mathematica often just referred to as Principia, in which he explains his ground braking theory of gravity (among other things).

newtmtnThe image we show here of a canon on top of a mountain is from a later popularised version of the Principia. The idea is to fire the cannon, which is supposedly well above the atmosphere, with increasing charge and thus initial speed of the cannon ball. The latter will fall down to Earth at increasing distance, but there will be a speed at which the cannon ball will never hit the ground; it will continue to fall around the Earth. In practice this is impossible because of the Earth’s atmosphere and mountains that are not that tall, but as a thought experiment it is quite illustrative.
As a matter of principle the cannon ball, orbiting the Earth will come back to the same spot where it left the cannon, therefore if this was possible, the gunner would himself be struck by the projectile he had fired a while ago.

Look at the animation of this experiment
Gradually increase the firing speed and see what happens. At which minimum speed will the cannon ball come back to point V in the diagram? (At higher speeds the cannon ball will disappear from Earth. We will come back to that below).

This experiment illustrates that a satellite orbit actually is a perpetual free fall in the gravity field of the central body, the Earth in our case. But, as Newton realised, this holds for all orbital motion in space, e.g. the motion of the Moon around the Earth and of the planets around the Sun.

So why are astronauts in the ISS weightless?
Because they are in a constant free fall motion around the Earth. And the space station itself and everything else in it is in that same free fall. The Earth’s gravity is the very reason they are moving that way. The term “zero-gravity” is therefore misleading. It is much more accurate to say “weightless” because while everything in orbit is accelerating in the direction of the Earth’s centre (like the cannon ball), there is no weight force like you would experience while standing on the surface of the Earth.

Let us now talk a bit more about orbits and how to move in space.

Read more ...

Enlightening the Future: The Quality Lighting Teaching Kit

User Rating: 0 / 5

Star InactiveStar InactiveStar InactiveStar InactiveStar Inactive

The CIE National Committee of New Zealand (International Commission of Illumination) is supporting a program developed by the NOAO to promote Education & Public engagement on better quality lighting. The kit was inspired by the International Year of Light and was funded by the Optical Society of America (OSA) Foundation, the International Astronomical Union (IAU) and the U.S. National Optical Astronomy Observatory (NOAO). Using quality lighting, the QLT kit allows students to creatively problem-solve six realistic cases on how light pollution affects wildlife, the night sky, our eyes, energy consumption, safety, and light trespass into buildings.

LightingKitThe activities are optimized for 11-13 year olds but can be expanded to a year younger and a few years older. Most of the activities can be done within in a few minutes with the exception of the Energy Activity. The activities can be done during class or in an afterschool program and as stations that the students rotate through or as stand-alones, one at a time. The goal is to increase student and public awareness of light pollution issues and “quality lighting” solutions. There is an extensive support for the kit contents and activities at this website address:

CIE-NZ will be very interested to promote this initiative through New Zealand, and will be glad to loan the kit.
Please contact me for further information.

Dr. Francois Shindo
Research Scientist
Photometry & Radiometry
Measurement Standards Laboratory
Gallaghan Innovation
DDI: 04 9313732
This email address is being protected from spambots. You need JavaScript enabled to view it.


STARMUS III - Epilogue

User Rating: 5 / 5

Star ActiveStar ActiveStar ActiveStar ActiveStar Active

logo header 200x68





Thursday 30 June (Asteroid Day) saw a round-table discussion in the great dome of the La Palma Observatory Roque de los Muchachos.
This was streamed live to the venue at Teneriffe. Discussed were planetary defence in view of Asteroid Day, abrupt climate change and science communication. An interesting discussion, very well lead by Russell (Rusty) Schweickart, but without clear results as could be expected.

Friday 1 July we first had organised a private excursion to the Teide Observatory in the morning, and in the afternoon it was the last day of STARMUS 2016 with the SONIC UNIVERSE CONCERT held in the Auditorio de Tenerife Adán Martín in Santa Cruz. This was a very special concert with performances by:

Sarah Brightman & Tenerife Symphony Orchestra at special request of Stephen Hawking,
ANATHEMA with Stephen Hawking himself participating in their first song,
Chris Hadfield & Rick Wakeman Space Oddity (David Bowie),
Rick Wakeman Life on Mars (David Bowie).

Read more ...

STARMUS III - Wednesday 29 June

User Rating: 5 / 5

Star ActiveStar ActiveStar ActiveStar ActiveStar Active

logo header 200x68

Wednesday 29 June 2016



image2Stephen Hawking opened this session with a talk entitled “A brief History of Mine”.

Born on 8 January 1942 in Oxford he had an unremarkable time as a student at various schools until he started with his PhD study. At that time Cosmology and Gravity were areas that were ready for development. His first book was “The large scale structure of Space Time” written with Ellis (1973).

Stephen Hawking 8 January 1942 with his parents

Stephen talked about how he discovered the relationship for entropy of a Black Hole. Around 1982 he shifted his attention to the very early Universe. As we know modern cosmology has developed to be a precision science starting with the CMB structure observed by the WMAP satellite in 2003 and with the greatly improved latest results from the ESA Planck satellite, which give a “blueprint for all structure in the Universe”. He became very ill when he was working on his bestseller “A brief History of Time” but completed it as he was motivated by the notion that science must be explained to the general public.

Referring to the recent LIGO results he suggests that some day we may be able to use gravitational waves to look back to the Big Bang itself. It is an exciting time to be alive, witnessing 50 years of major improvements of our understanding of the Universe. He concluded with the advice to look up to the stars rather than to your feet, to be curious and to “just not give up”. He received a standing ovation for several minutes from an excited 1000+ audience.

Read more ...

Latest News

As real as it gets - Flying above Mars

mars flyover JF

Finnish filmmaker Jan Fröjdman transformes imagery from HiRISE, a camera aboard the Mars Reconnaissance Orbiter, into a dynamic overhead view of the Red Planet.

Watch it here.


Great Overview New Horizons mission

alan stern copyMeet Dr. Alan Stern, the Principle Investigator and learn about NASA’s historic mission to Pluto and beyond. Live stream on 13 February 2017 (can be watched again) here.

Introduction to Astronomy restarts

IntroAstro copy

Highly recommended Ronen Plesser’s free course Introduction to Astronomy will now be offered at Duke University on their new platform Duke Extend. The new session of Introduction to Astronomy starts November 28, and you can learn more and register here.

This ten week course progresses outward from our own Earth into Solar system, Galaxy and Deep Space, to cover essentially everything in the Universe. Watch Ronen's introduction on YouTube here.

Visit Rosetta’s comet in amazing 3D.

Rosetta 3D copy

Rosetta spacecraft has impacted on comet 67P/Churyumov-Gerasimenko, ending its very successful mission. You can view the comet in this amazing interactive 3D visualisation here.
Find a description of the tool here.

Are we heading for a new Maunder Minimum?

2016 09 01 1472723838 9260456 Solar Cycle Prediction

Original image here.

We are coming out of the current sunspot cycle 24 which will end around 2019. The maximum of this cycle has yet again been well below that of the previous two cycles.

“Some studies show that sunspot magnetic field strengths […] are already close to the minimum needed to sustain sunspots on the solar surface”.

Read Dr. Sten Odenwald’s Blog here.

ESO Astronomy Camp

ann16031aStudents aged between 16 and 18 years old, can apply for participation in the 4th ESO Astronomy Camp. The camp will take place from 26 December 2016 to 1 January 2017 in Italy and it is organised by ESO and its Science Outreach Network, together with the science education event organiser Sterrenlab and OAVdA.

Click the link 4th ESO Astronomy for detailed information.

Teachers invited to join the STEAM Team

STEAMThe Planetary Society is developing a youth education program with the goal to help teachers educate and engage students around the world in Science, Technology, Engineering, Math, and the Arts.

The STEAM Team is an advisory network of educators from around the world who will help to create the most effective education program possible. We want to bring your educational expertise to bear on a widespread program to enhance STEAM education around the world.

By joining this team, you will become part of a global advisory council of educators. We will reach out to you for feedback on the educational resources we develop, and on the direction of our youth education program as a whole. We’ll send you surveys, questions, and opportunities to share your ideas.

Read more here

What happens at the edge of the Universe?

EdgeoftheUniversePBSWhat is at the edge of the Universe and what happens if we are trying to get there.
In this episode in the Space Time series by PBS Matt tries to answer this question in a scientific way.
Watch it here.

Join PBS on Facebook