BAN #211: Help New Horizons target the nearest stars

20 April 2020   Issue #211

April 20, 2020

Subscribers make me happy to Pluto and beyond.

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

The New Horizons spacecraft is now a staggering 7.1 billion kilometers from Earth, the very, very distant Sun at its back, with that distance increasing by an astonishing 14 kilometers every second.

Pluto is far behind, as is Arrokoth, its most recent solar system attraction that it briefly blew past on January 1, 2019. But now New Horizons is heading into the black, plunging into the dark void between stars.

[Artwork of New Horizons as it passed Pluto and its moon Charon in 2015. Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)]

But its mission isn’t quite over. Not yet. There are, it turns out, still stars to see. And, if you’re an amateur astronomer, the New Horizons team wants your help to see them.

The stars in question are the closest star to the Sun, Proxima Centauri, and another dim red dwarf called Wolf 359 (and if that name sounds familiar, well, click on that link to Make It So).

On the 22nd and 23rd of April, 2020, New Horizons will turn its detectors toward those two stars, taking images of them against starry backgrounds. The New Horizons team wants astronomers back on Earth to take images of these same stars at the same time, turning this effort into the longest baseline parallax observation ever made.

Oh, do I love this idea.

Parallax is a perspective effect, where, as you move, something near to you seems to change position more than something far away. Here, let this guy explain it. I hear he’s good:

The easiest way to show parallax is to hold your thumb up at arm’s length, and close your left eye. See where your thumb appears to be compared to background objects. Now switch eyes; close your right eye and open your left. Your thumb appears to move! That’s because the angle one eye sees your thumb is slightly different than the angle your other one does. The amount your thumb moves depends on how far apart your eyes are (what’s called the baseline) and how far away your thumb is. Bring your thumb in closer and try again; it’ll appear to move a lot more.

This is a critical effect for astronomy. Stars are incredibly far away; even the nearest are dozens of trillions of kilometers distant. Alternating eyes won’t help you here! But we can use a much longer baseline: The orbit of the Earth. If we observe a star in, say, January, then observe it again in July when the Earth is on the other side of its orbit around the Sun, our baseline goes from a few centimeters to 300 million kilometers. The parallax angle is still small, but easily measurable with the proper equipment.

[Wolf 359 (top image, center) and Proxima Centauri (bottom; the bright star just left of center) as seen in late 2019. The green circle is where New Horizons is predicted to see the stars, due to both parallax and the motions of the stars through space. Credit: William Keel/University of Alabama/SARA Observatory]

But with New Horizons we have an opportunity to measure parallax directly without having to wait so long! Since it’s well over 7 billion kilometers from Earth, the angle at which it sees nearby stars relative to more distant ones is very large compared to viewing them from Earth. If astronomers here take images at the same time the spacecraft does, they can be compared directly to determine the stars’ parallax.

Now mind you, this observation probably won’t be any more accurate than what we can do with sophisticated equipment now; the Gaia observatory has been doing these kinds of measurements for years and has ridiculous accuracy. But this experiment isn’t done so much to get scientific accuracy as it is to get people on Earth involved, to set a record, and to demonstrate that spacecraft very far from Earth can perform observations like this to determine their position; the ultimate “navigation by starlight”.

You can read about what they’re looking for and what you can do to participate on the New Horizons Parallax Program page. At that page you’ll find info about this program including timing and finder charts for the stars.

Proxima Centauri is a dim red dwarf about 4.24 light years away. As the name suggests it’s in the constellation of Centaurus, which is a southern hemisphere constellation. It’s only visible if you live south of 28° north latitude, and realistically you need to be much farther south to see it clearly. From Sydney, Australia, for example, it’ll be high in the south after about 10 p.m. local time in late April.

Wolf 359 is also a red dwarf in the constellation Leo, which is well placed for northern hemisphere observers in late April — it’ll be high to the south/southwest by the time the Sun goes down and it’s dark out.

Both stars are faint — Proxima is 11th magnitude and Wolf 359 is 13th (the faintest star you can see is 6th mag, and the scale is logarithmic) so you really do need a decent telescope to get images of them. Mind you, both are among the physically closest stars in the sky to us (which is why they were chosen, to maximize the parallax effect), yet both are really faint, attesting to how dim red dwarfs are. It always amazes me that the closest star to us in the entire Universe (besides the Sun of course) is too faint to see with the naked eye.

But they can be seen with telescopes, both here on Earth and another literally past all the known planets in our solar system. By seeing these stars at the same time using both sets of telescopes, we can directly grasp the size and scale of our local neighborhood in the galaxy… and from there, the size of the entire visible Universe.

And now you can be a part of that, too.

Tip o’ the dew shield to astronomer Tod Lauer for this news.

Blog Jam

What I’ve recently written on the blog, ICYMI

[Artwork depicting the explosion of a massive star: a supernova. From Tuesday’s article. Credit: M. Weiss ]

Et alia

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