comet dust – The Amazing Sky

December 6, 2013December 7, 2013

Zodiacal Light and the Phantom Comet

The Zodiacal Light shines bright in the New Mexico dawn, near where the ill-fated Comet ISON would have been.

This was the dawn sky on the morning of December 6, 2013 looking east from our observing site at the Painted Pony Resort in New Mexico.

The zodiacal light was bright pre-dawn extending up from the horizon to high overhead. This glow is from sunlight reflected off comet dust in the inner solar system.

Adding to that cloud of dust is presumably the remains of Comet ISON (C/2012 S1) – this image includes the position where ISON would have appeared had it survived, with its head left of centre, just left of the zodiacal light, and just above the mountain ridge. Its tail would have arched up and to the left, had it grown an extensive dust tail as was hoped.

As it is, there is a comet in the field – Comet Lovejoy (C/2013 R1) is a tiny blue blip at far left, a minor consolation prize for missing ISON. Pity ISON didn’t work out, as we would have had two photogenic and naked eye comets in the dawn sky together.

The field also contains two planets: Mars in Leo above and right of centre, and Saturn in Libra just coming up over the mountains in the middle of the zodiacal light. Both lie in the zodiacal light because the light follows the ecliptic – i.e. the plane of the solar system and the orbits of the planets.

October 10, 2013

Zodiacal Light – Dawn’s Early Light

The ghostly glow of comet dust brightens an October dawn.

This is the zodiacal light, as it appeared two mornings ago in the pre-dawn sky from my backyard in southern Alberta. This tapering glow angled up from the horizon is best spotted in the eastern sky on clear and moonless autumn mornings, like this one.

What you are seeing is sunlight reflected off dust left by passing comets in the inner solar system. So while this glow looks like it might originate in our atmosphere it really comes from dust out in interplanetary space.

This subtle glow, often called the “false dawn,” appears in the hour or so before the true dawn begins to brighten the sky too much (its purple light is just starting to light the horizon here).

Also visible here: Sirius at far right, Jupiter above centre, the Beehive star cluster below Jupiter, and Leo rising embedded in the zodiacal light, with Mars just above Regulus, Leo’s brightest star. The planets lie along the zodiacal light because the dust that causes it also lies in the same plane as the orbits of the planets, the ecliptic plane.

I shot this with a 14mm lens for a stack of four 2-minute tracked exposures, but with the horizon coming from just one of the exposures to minimize blurring from the moving camera slowly following the sky.

March 19, 2013

The Zodiacal Light from the Desert

From a dark site the glow of Zodiacal Light rivals the Milky Way in brightness.

This was the scene every night last week in the evening sky from our New Mexico observing site. The vertical glow of Zodiacal Light was a source of natural light pollution brightening the western sky. I’ve never see it more obvious in the west and this was the perfect season to see it. In March from the northern hemisphere the ecliptic – the plane of the solar system – is angled high into the western sky, almost vertical from the latitude of southern New Mexico.

The Zodiacal Light lies not in our atmosphere but comes from interplanetary space, and follows the ecliptic. What we were seeing was a glow of sunlight being reflected off fine dust particles orbiting the Sun in the inner solar system, likely spread by passing comets like PANSTARRS. I blogged about the Zodiacal Light last month, in photo taken from home in southern Alberta. You can also read about it at the excellent Atmospheric Optics website.

You don’t need to be in the desert to see it, but you do need dark skies. And no Moon in the sky.

At last week’s dark of the Moon period, Jupiter sat at the apex of the Zodiacal Light, just above the Pleiades star cluster. Near the top, right of centre, you can also see a short satellite trail, likely from a flaring Iridium satellite.

February 9, 2013

The Subtle Glow of Comet Dust

Out of the skyglow from lights and the remains of twilight rises a tapering pyramid of light. It’s one of the night sky’s most subtle sights for the naked eye.

This is the Zodiacal Light, and I’ve been trying to capture it in the evening sky from home for a number of years. Last night was a good night for it. The sky was very transparent, for the first couple of hours at least. An ultra-wide angle lens allowed me to capture the Light in context with the wider sky, towering out of the southwest at right, reaching up to the Pleiades and Jupiter high in the centre of the frame. The Milky Way is at left. Everyone knows the Milky Way but the Zodiacal Light is less famous.

It’s visible only in the hour or two after sunset or before sunrise. Late winter and spring are the best times to see it in the evening sky. That’s when the ecliptic – the plane of the solar system where the planets lie – is tipped up at its highest angle above the horizon putting it above obscuring haze. The Zodiacal Light lies along the ecliptic because it is part of our solar system, not in our atmosphere. It is sunlight reflected off dust orbiting in the inner solar system that’s been cast off over thousands of years by comets passing through. It is brightest closest to the Sun and fades out at greater angles away from the Sun. Thus its tapering appearance in my sky as the photo shows, very much as my eye saw it.

It takes a good night at a dark site to see the Zodiacal Light. But take a look at the next dark of the Moon. You’ll be surprised at how easy it is to see once you know what to look for.

December 7, 2012December 7, 2012

Catching the Zodiacal Light

From a truly dark sky site, subtle sky glows become obvious. This is the Zodiacal Light of evening.

The Sun has long set and the very last glow of twilight is colouring the sky just above the hills. But reaching up from the sunset point in the northwest is a long triangular glow extending far to the south. This is called the Zodiacal Light – it does not originate in our atmosphere but is from sunlight reflecting off comet dust orbiting the inner solar system in the same plane as Earth’s orbit. Or at least that’s where we see it appearing the brightest, as a glow brightest near the Sun and extending along the ecliptic plane, where we find the constellations of the Zodiac. Here it appears in Capricornus and Aquarius.

I shot this two nights ago, from Coonabarabran, Australia, so the orientation of the Zodiacal Light is different from what we see from the Northern Hemisphere. Here it extends up from left to right. From home in Canada – and you can see the Light from northern latitudes on a dark night – it would be angled up from right to left, a mirror image of what we see here.

The subtle glow of Zodiacal Light is best seen in the evening sky in spring, no matter your hemisphere. I took this on December 6, 2012, still officially spring in the southern hemisphere if you assume southern summer starts on the solstice, December 21. However, Australians say summer begins December 1, so this is a portrait of the Zodiacal Light on a warm summer evening down under.