- Email: [email protected]
Stargazing at home: Earth's celestial moment
The back pages Puzzles Cryptic crossword, an egg puzzle and the quick quiz p52
Feedback Elongated eels and naming names: the week in weird p53
Picture of the week Our pick of your future-themed photos p53
Almost the last word Lightning effects and biscuit/cake duality: readers respond p54
The Q&A Randall Munroe on the creative use of science p56
Stargazing at home Week 1
Earth’s celestial moment It’s almost the September equinox, making this the perfect time to kick off our exploration of the heavens with Abigail Beall
Abigail Beall is a science writer in Leeds, UK. This series is based on her book The Art of Urban Astronomy @abbybeall
What you need Cardboard Two balls Wire Sticks Glue and scissors
For next week A clear night sky
Next in our 7-week series 1 Model the equinox 2 Find the North Star and Southern Cross Learn to navigate by the stars 3 Test your area’s light pollution 4 Identify the craters of the moon 5 Orion and Sirius: how to star-hop 6 Planet spotting: Mars, Mercury and Uranus 7 Taurus and the zodiacal constellations
EVER looked up at the night sky in wonder? Ever wished you could spot Mars or navigate by the stars? Then our new astronomy series is for you, wherever you live in the world and even if you are in a lightpolluted city. Better still, no special equipment is required. Crucial to making sense of the night sky is understanding Earth’s movement around the sun. As an equinox falls on 23 September, I’m going to kick off the series with a simple model to explain what it is. There are two equinoxes in the year; they are the points when the lengths of day and night are nearly equal over the world. The one in September is when the southern hemisphere begins to tilt slightly more towards the sun and spring begins. In the north, it marks the start of autumn, or fall. The equinox isn’t a day-long event, however. It is the exact moment when the sun crosses the plane of Earth’s equator, which varies according to your latitude. The model we are making won’t be to scale, but that’s OK for our purposes. Start with a circular piece of card. Cut another piece into a rectangle the same length as the circle’s radius, like the one in the picture. Then pierce a hole at one end of your rectangle and at the centre of your circle and push a stick through both. Glue a ball on top to represent the sun. Next, bend a piece of wire to 23.5° – that is the angle of Earth’s axis of rotation – and stick it into the other end of your rectangle. Pierce the poles of your “Earth” ball and stick the wire through.
23.50
ANGLE OF EARTH'S TILT
PRECESSION EARTH SIDE-ON TO SUN AT EQUINOX
Stargazing at home online
Projects will be posted online each week at newscientist.com/maker Email: [email protected]
Now move your Earth around the sun, keeping your polar wire pointing in the same direction at all times. You’ll come to a point at which the northern hemisphere tilts towards the sun. This is the June solstice, marking the northern summer. As you move your Earth further round its orbit, it will reach a point where both hemispheres face the sun the same amount – this is where we are now, the September equinox. When the south pole tilts most to the sun, you have reached the December solstice, and the March equinox comes when both sides are equal again. The tilt of Earth is also moving,
in a process called precession. To simulate this, hold the end of the wire protruding from Earth’s north pole and make it trace a small circle (see picture). This rotation takes 25,772 years to complete, meaning that in around 13,000 years’ time, summer in the northern hemisphere will happen when it currently experiences winter. It also means the North Star will change, because the north pole will no longer be pointing in the same direction. Instead of Polaris, the bright star Vega will be the north star. Which brings us to next week, when we’ll be using what we have learned to find the North Star and the Southern Cross. ❚ 21 September 2019 | New Scientist | 51
Feedback Elongated eels and naming names: the week in weird p53
Picture of the week Our pick of your future-themed photos p53
Almost the last word Lightning effects and biscuit/cake duality: readers respond p54
The Q&A Randall Munroe on the creative use of science p56
Stargazing at home Week 1
Earth’s celestial moment It’s almost the September equinox, making this the perfect time to kick off our exploration of the heavens with Abigail Beall
Abigail Beall is a science writer in Leeds, UK. This series is based on her book The Art of Urban Astronomy @abbybeall
What you need Cardboard Two balls Wire Sticks Glue and scissors
For next week A clear night sky
Next in our 7-week series 1 Model the equinox 2 Find the North Star and Southern Cross Learn to navigate by the stars 3 Test your area’s light pollution 4 Identify the craters of the moon 5 Orion and Sirius: how to star-hop 6 Planet spotting: Mars, Mercury and Uranus 7 Taurus and the zodiacal constellations
EVER looked up at the night sky in wonder? Ever wished you could spot Mars or navigate by the stars? Then our new astronomy series is for you, wherever you live in the world and even if you are in a lightpolluted city. Better still, no special equipment is required. Crucial to making sense of the night sky is understanding Earth’s movement around the sun. As an equinox falls on 23 September, I’m going to kick off the series with a simple model to explain what it is. There are two equinoxes in the year; they are the points when the lengths of day and night are nearly equal over the world. The one in September is when the southern hemisphere begins to tilt slightly more towards the sun and spring begins. In the north, it marks the start of autumn, or fall. The equinox isn’t a day-long event, however. It is the exact moment when the sun crosses the plane of Earth’s equator, which varies according to your latitude. The model we are making won’t be to scale, but that’s OK for our purposes. Start with a circular piece of card. Cut another piece into a rectangle the same length as the circle’s radius, like the one in the picture. Then pierce a hole at one end of your rectangle and at the centre of your circle and push a stick through both. Glue a ball on top to represent the sun. Next, bend a piece of wire to 23.5° – that is the angle of Earth’s axis of rotation – and stick it into the other end of your rectangle. Pierce the poles of your “Earth” ball and stick the wire through.
23.50
ANGLE OF EARTH'S TILT
PRECESSION EARTH SIDE-ON TO SUN AT EQUINOX
Stargazing at home online
Projects will be posted online each week at newscientist.com/maker Email: [email protected]
Now move your Earth around the sun, keeping your polar wire pointing in the same direction at all times. You’ll come to a point at which the northern hemisphere tilts towards the sun. This is the June solstice, marking the northern summer. As you move your Earth further round its orbit, it will reach a point where both hemispheres face the sun the same amount – this is where we are now, the September equinox. When the south pole tilts most to the sun, you have reached the December solstice, and the March equinox comes when both sides are equal again. The tilt of Earth is also moving,
in a process called precession. To simulate this, hold the end of the wire protruding from Earth’s north pole and make it trace a small circle (see picture). This rotation takes 25,772 years to complete, meaning that in around 13,000 years’ time, summer in the northern hemisphere will happen when it currently experiences winter. It also means the North Star will change, because the north pole will no longer be pointing in the same direction. Instead of Polaris, the bright star Vega will be the north star. Which brings us to next week, when we’ll be using what we have learned to find the North Star and the Southern Cross. ❚ 21 September 2019 | New Scientist | 51