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SYFY WIRE Bad Astronomy

Poli'ahu: Time-lapse of telescopes and stars dancing under Hawaiian skies

By Phil Plait

I suddenly realized: I’ve been writing at Syfy Wire for over three months, but I haven’t posted an amazingly beautiful and way cool time-lapse night sky video yet!

Well, let’s fix that. Behold: POLI’AHU!

The footage in this video was taken by my friends Harun Mehmedović and Gavin Heffernan. If those names are familiar, it may be because I recently wrote about their new astrophotography book, SKYGLOW, for which they traveled the US taking gorgeous photos of the night sky. They did this to raise awareness about light pollution, and, in fact, POLI’AHU is part of that project (they’ve made several videos, and they’re all very much worth your time to watch).

Poli’ahu is one of four Hawaiian goddesses of snow, and in legend lived on Mauna Kea, one of the five large volcanoes making up the Big Island (she was an enemy of the volcano god Pele, who, honestly, had a lot of enemies) and is an apt name for the video, taken from various spots at the volcano’s peak (where it does sometimes snow). The summit reaches a lung-straining 4200 meters (nearly 14,000 feet) above sea level. Because of this, it resides above a large fraction of the atmosphere, making it a very desirable location for astronomical observatories. Quite a few are situated near the peak.

You can see quite many of them in the video (including a dramatic view of NASA’s Infrared Telescope Facility at the time mark 2:06). They provide a nice foreground to the drama in the sky.

zodiacal light

There’s a lot to see above Hawaii in this video. My favorite part starts at the 2:40 mark. The Milky Way, nearly parallel to the horizon, begins to lift itself up into the sky. It’s magnificent, but if you look carefully, there’s much more to see. At the lower left, red ripples move across the sky; that’s airglow, caused by molecules in the upper atmosphere releasing energy they accumulated from the Sun during the day in a process called chemiluminescence.

On the horizon, just right of center, is another red glow, but this is due to the lava pool in the Halema’uma’u crater on Kilauea. I’ve seen this myself (I’d been twice before but never saw the actual lava; third time’s the charm) and it’s an extraordinary thing to witness.

But we’re not done. Just barely visible in that video sequence is a faint, pearly glow starting on the horizon behind the observatory in the middle and stretching up to the right toward the center of the Milky Way’s bulge (it can help to back away from the picture so details blur and you see more of the general structure). I had to check a star map to be sure, but this is zodiacal light, the reflection of sunlight off of the material shed from ancient dead comets. It’s very difficult to observe, especially if you have even mild light pollution (I’ve never seen it myself).

It’s called zodiacal light because it’s always seen in the zodiac constellations; those are the star patterns through which the Sun and planets appear to move over the year. That’s no coincidence; the solar system is flat, and we’re in it, so we see it as a line in the sky. Those comets were affected by Jupiter and orbited the Sun in that same plane, so the glow from their dust follows that same line.

This scene just reinforces the reason Harun and Gavin made this video: To remind us of what we can see with dark skies, and what we lose when we don’t. If you’ve never been to a dark site I can’t suggest visiting one strongly enough, even if just once in your life. To see the heavens laid out above you in the glory they truly deserve is something that will leave you with a greater appreciation of the sky, and the wonder and joy astronomers are privileged to feel every single day. And night.