New Horizons is one of my favorite space probes. Very few have gone that far and have given us so much back in return. Launched in 2006 and after flying for nine years it finally reached Pluto to delight us with spectacular images of the dwarf planet, it also broke the record for the photograph taken farthest from Earth. Now, on the edge of the Solar System already, it surprises us with something new: photographs of stars, the same ones that we see from Earth but in a different position.
If the stars are technically fixed, how is it possible that New Horizons sees them in a different place than we see them? Simple, we see them from different points of view. From Earth, being so small in relation to the Universe, we see the stars equally from anywhere in the world. But New Horizons is not on Earth, it is 7 billion specifically from Earth. Such a distance has been sufficient for at least the stars closest to us to be seen in a different position.
On April 22 and 23 New Horizons photographed the stars Proxima Centauri and Wolf 359 respectively. Proxima Centauri is known to be the closest star to Earth after the Sun, it is about 4.24 light years from us. Wolf 359, which is a red dwarf, is almost 8 light years away. These two photographs overlapped others taken from Earth to the same stars. Outcome? Proxima Centauri is much closer to Wolf 359 in New Horizons photography.
The largest ‘parallax effect’ in history
This New Horizons landmark is not only a curiosity for astronomers, but also an important utility to better investigate and measure space. The photographs were taken with an idea behind it: to make the largest parallax effect in history.
The parallax effect has been used for centuries by astronomers to measure the distance of a distant object. The idea is that obtaining the relative distance from two different points and knowing the separation between those two points, the measurements of the object under investigation can be calculated. In the 18th century, one of the most ambitious scientific projects in history was conceived with the purpose of measuring the size of the solar system, and they did it with the parallax effect.
Today to see the stars from different positions and thus better measure distances, astronomers take advantage of the Earth’s orbit throughout the year, this gives them a distance of about 300 million kilometers. But the larger the distance between the two positions, the more accurate the measurement is. Billions of miles away, New Horizons has given us the most impressive parallax effect of all, the first interstellar. A parallax effect large enough to see stars from different positions. And we are not far enough away yet to work with more stars, only the one closest to us.