Showing posts from March, 2020

Eccentricity and conical sections

  What, apart from a popular way of describing English people, is eccentricity? In astrophysics, it describes how flat orbits are. This includes orbits of planets, satellites, comets and even things that don't come back, such as Oumuamua. Most people will tell you that planets orbit around the Sun in a circle. It's close. The Greek astronomer Ptolemy certainly thought so. But, by about the 15th Century, astronomers (mainly led by the Arabic schools) had realised there was something not quite right with circular orbits. It fell to an observer and a mathematician to figure it out. Tycho Brahe - the Great Dane - was the observer. He built a series of machines, some of which were enormous. These made exquisitely precise measurements of the positions of the planets in relation to the stars. The maths genius was Johannes Kepler, who was Tycho's student. Kepler knew there was something screwy about Mars - it was never in quite the "right" position. But Tycho wouldn't

Binocular designations

To be honest, I’ve been putting this one off for a while because the mathematics turns my brain into a Möbius strip. I’ll try to keep it understandable! One of the common questions that people buying binoculars ask is “ what do these numbers mean? ” The important ones are the “8x42”, “20x100”, or others in the photos. These tell you the magnification and aperture of the binoculars. Magnification and aperture Magnification , the first number, is pretty simple. If you’re looking at something through a pair of 10x binoculars, whatever you’re looking at will appear one tenth of the distance away. The aperture is the diameter of the big lens at the front of the binocular, measured in millimetres. It relates to the light-gathering ability of the binoculars. On a bright day, this may not be important. But if you’re hunting owls or star gazing, it's critical. The more light you get in, the more you can see. Magnification and aperture interact as well. The more magnification

Autumn Equinox list for observing

The Autumn Equinox is tomorrow, the 21st of March. I've prepared a list of things for you to find. Remember, the the new Moon is on Tuesday (the 24th). If you’ve got a small scope, such as a refractor, star clusters work best for you. If you've got a larger aperture, you can see dimmer objects, such as my Running Chicken. I've ordered it by the time each object passes the meridian, so start at the top of the list. As to planets, Venus is low in the west in the evening, still bright enough to be seen in the sun’s glow, and a pleasing crescent. Mars, Jupiter and Saturn are clustered before sunrise. Clear skies! Galaxy: Large Magellanic Cloud (06:43 PM) Globular cluster: M 79 - (06:43 PM) Bright nebula: M 1 - Crab Nebula (06:57 PM) Bright nebula: M 43 - De Mairan's (06:57 PM) Diffuse nebula: M 42 - Orion Nebula (06:57 PM) Bright nebula: NGC 1977 - Running Man (06:57 PM) Bright nebula: NGC 2070 - Tarantula Nebula (06:57 PM) Dark nebula: B 33 - Horsehead Nebula (07:12 PM) D

2020 CD3 (another temporary moon for the Earth)

How many moons does the Earth have? I've been watching QI for years. It's got to be one of the favourite shows for the "well, actually" crowd. One of the themes in the show is that Stephen (lately Sandi) asks a plain question, and one of the panel gives the answer that everyone thinks is right. This is a trap. One? Wrong! A while back, Stephen Fry talked about Cruithne, and claimed it was a moon of the Earth's. I wrote about this about a year back in one of my Facebook posts. So two? Wrong! The question has come up a number of times on the show, always with different answers. It's turned into a standing joke. But - for the last few months, Earth has had another companion, and it's absolutely tiny. It doesn't have a name, apart from 2020 CD3, and appears to be a captured asteroid, of between two and four metres in size. Because it hasn't been under observation for long, we really don't know when it showed up, but the orbital models indicate at l

Narrowband Palettes

Caution - weird photographs ahead!   Getting the colours You might remember me talking in the past about the different ways you can represent the light you capture in your camera. You can display red light as red, but more interestingly, you can display the light that comes from different elements as different colours on your computer display. This is particularly good for separating light from two gases, say, Hydrogen and Sulphur, which are both reds. You can display one as red and one as green. When I take photos, I use filters to capture different colours. For foreground stars, I typically capture using broad “red”, “green” and “blue” filters, and for background nebulas I use Hydrogen, Oxygen and Sulphur “narrowband” filters. Presenting the colours Later on, in my imaging process, I recombine these channels in any way I find aesthetic. A couple of weeks ago, a new version of my image processing software ( Astro PixelProcessor ) was released. One of the new features is that I can

Betelgeuse, Betelgeuse, Betelgeuse!

Dimming update? Back at the end of December, I posted that the red supergiant Betelgeuse, in the constellation of Orion, was dimming visibly . It used to be one of the brightest stars in the sky, and now it’s not even in the top 20. Yes, it’s less than half as bright as it was just over a year ago. Red supergiant stars such as Betelgeuse normally end their lives in supernovas, which would be seriously cool to see. We’d be quite safe here, at a good enough distance, but we’d be able to see the explosion as it happened during the day, and it’d be months before it dimmed. There are other possible explanations for what we’re seeing. One theory that might be quite feasible is that a large and dense gas cloud has passed in front of the star. This sort of thing does happen, and would explain the phenomenon quite well. Since the star’s dimming has been in the news, more and more people have been watching it. Most recent reports suggest that the rate at which it’s dimming