Space, Stargazing

Stargazing 101- comets and new kit

Last night I managed to convince my dad to go comet hunting with me, so we trekked over to the field (as our garden is surrounded by annoyingly tall trees that block the sun at 4:30 and any stars that aren’t directly overhead) to try catch a glimpse of Comet Neowise before it disappeared. We were in luck! It is actually surprisingly easy to see with the naked eye- just find Ursa Major (The plough/big dipper) and look down- we could see it even standing next to a street light (though of course it was much easier to see under darker skies). Unfortunately it is getting dimmer now (also depends on local light pollution/weather +your eyesight), so is less impressive- though still awesome through a camera/binoculars/telescope.

My dad had carried down the telescope, so we had that (Celestron 114 LCM computerised reflector), a tripod, my camera (Nikon D3200), and two new bits of kit to attatch the camera to the telescope (A T-ring and T-adapter)!

We looked at Neowise first through the telescope, and then took some pictures- here are the close ups!

What can we actually see here?

Well the rocky ice nucleus is tiny, not visible on here, so the bright area is the halo surrounding it, made of sublimated gases, forming a ‘coma’ around the central nucleus. The dust and gas released into the coma is then pushed away by the pressure of the solar wind, creating the long dust tail you see behind it! This dust tail always points away from the sun. The colour of the coma/halo depends on the chemical composition of the comet, as it is emitted from the gas particles in the halo, rather than being light reflected off of it from the sun. This is because the ultraviolet light from the sun excites the atoms and causes the electrons to jump around, and emit light. The wavelength of the emitted light corresponds to the compound/molecule emitting it. Comets tend to have this eerie blue-green colour, which is emitted by two compounds: Diatomic Carbon (C2) and Cyanide/Cyanogen (CN), which are the main compounds found in the coma!

You can see the dust tail here really clearly! These were taken with a few seconds exposure (I think the selfie was 6 seconds and the other was 8-10) and a high ISO, then a little bit of editing to change the brightness etc.

I couldn’t see it on any of my photos unless I squint (so I doubt its actually there), but the comet also has another fainter tail- the ion tail! You can see it better in these amazing photos from Dr Becky Smethurst on Instagram and Ian Lauer’s Instagram! The day my astrophotography gets even half as good as these guys’ will be a good day!

Follow Ian here

The dust tail is wide as all the particles are different sizes, so are released at slightly different speeds, so end up in slightly different orbits, making it curved. The ion tail is thinner and always points straight away from the sun, as it is always made of CO+ ions, which are all the same size, and are charged so are swept into a straight line from interaction with the sun’s solar wind, also charged particles! There is also a 3rd tail that has just been discovered- the sodium tail. Like the ion tail, it is straight and points away from the sun, but forms later and is within the the dust tail! The images have only recently been published and not yet peer reviewed, but it’s still pretty cool!

A comet's evolution as it approaches, passes through, and exits the inner Solar System.
via NASA

As Comet Neowise gets closer to the sun, the processes that cause the tail may increase and cause it to break up, but even if it doesn’t, this is still the only time you will see it, as it orbits once every 6800 years! Its orbit is highly elliptical, coming very close to the sun but extending out beyond the Kuiper Belt to at least 500 AU (AU= distance between sun and earth).

The Kuiper Belt is the belt of small icy bodies beyond the orbit of Neptune, so reaches from 30AU to 50AU (basically the same area in which pluto orbits, hence pluto isn’t a planet), and is probably the source of short period/periodic comets like Halley’s Comet. So where does this come from? Well beyond the Kuiper Belt is the Oort Cloud, also made of small icy objects, but much more spread out. We have never actually observed anything out that far, but it must be there to be the source of all the long period comets like Neowise! It extends from 1000-2000 AU to 200,000 AU (3 LY!!).

An illustration of the Kuiper Belt and Oort Cloud in relation to our solar system.
via NASA

Let me know if you managed to see it, and send me any photos you get and I will feature them on my stories!

If you didn’t know, I have a youtube channel now, which you can find here

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