What you need
Clear night skies
Advertisement
A telescope (optional)
Any good astronomy app (optional)
OVER the course of a year, the sun traces a path in the sky. This invisible line, called the ecliptic, isn’t created by the sun moving, but instead by Earth travelling around the sun.
The solar system’s planets all orbit in a similar plane to Earth as it circles the sun – the biggest difference is Mercury, which is out by about 7 degrees. This means they can all be seen along the ecliptic in the night sky. The ecliptic is also where the zodiacal constellations are found and where eclipses occur, all of which make it one of astronomy’s most important features.
The moon doesn’t orbit exactly on the ecliptic. If it did, we would have a solar eclipse and a lunar eclipse every month. Instead, its orbit is angled at around 5 degrees compared with Earth’s around the sun. Eclipses occur when the moon crosses the ecliptic at a full or new moon.
Even though the planets’ orbits don’t line up exactly with the orbit of Earth, they can, like the moon, generally be used to gauge exactly where the ecliptic is in the sky. On any night when you can see a planet or two and the moon, you can trace the line of the ecliptic. At the moment, we can do it by watching the movement of Mars and the moon for a few days.
Mars and the moon are in conjunction on 18 February, with only 3 degrees separating them in the sky. This is about the same as the width of Orion’s belt. After this date, the two move further and further apart, largely because of the motion of the moon. This gives us a great opportunity to look at the ecliptic.
If you want to take part, pick a time in the 4 or 5 hours after sunset, not before sunrise. Try to look at the stars at around the same time each night for at least three days between 18 and 27 February.
Once you are set, go out and search for Mars, which will be in the south-west in the northern hemisphere and in the north-west in the southern hemisphere. It will be bright with a glowing red hue. If you are uncertain, use an app to ensure you have the right target.
Next, find the moon. On 20 February, Mars and the moon should still be close together. As the nights go on, the moon will appear further to the east, and by the end of this period, it will be low in the eastern horizon just after sunset. Mars will move much more gradually, so can be used to remind you where you saw the moon on the first evening. The line that the moon has traced across the sky over these nights is the ecliptic.
At the moment, you can only use the positions of Mars and the moon in the sky to find the ecliptic, but you can observe it on most nights if you can spot a planet or the moon. During the day, it is easier to find it, of course: you just have to watch the sun. But remember, whatever you do, don’t look directly at it.
Abigail Beall is accompanying a New Scientist Discovery Tour to Chile, the world capital of astronomy in November 2021.
Abigail is also the author of The Art Of Urban Astronomy (Buy from *)
Stargazing at home appears every four weeks
Next week
Science of gardening
These articles are posted each week at
(*When you buy through links on this page we may earn a small commission, but this plays no role in what we review or our opinion of it.)
