Archives For Moon

UK Eclipse 2015 Photos

March 20, 2015 — 2 Comments

Partial Eclipse 9am

Today’s partial Solar eclipse is off to a great start here in Witney, where the cloud cover is working as a perfect solar filter.

Partial Eclipse

The eclipse culminated here as a smiling, Cheshire cat-style grin 🙂

Partial Eclipse Grin

I got into a conversation recently about how some astronomical photos can totally change your whole perspective of yourself and your place in the Universe. There’s several images that come to mind right away – here are my own favourites:

1. The Milky Way (from a very dark location)

Milky Way

Seeing the night sky from a dark site is something most people don’t do very often, now that most of us live in cities. The vision of the Milky Way overhead can be startling, and a pair of binoculars make it more so; revealing that its delicate structure is made of millions of stars. This long-exposure photo of the dust lanes in our galaxy [1] is our first image that can really change your perspective on yourself and your place in the cosmos.

2. Earthshine on a crescent moon

Young Crescent Moon with Earthshine

When the Moon is just a thin crescent in the evening sky you can often see the rest of its face, dimly lit, and slightly reddened. This part of the Moon is not being illuminated by the Sun, like the crescent shape itself, but rather by the reflection of light from the Earth where the Sun has not yet gone down over the horizon. You’re seeing other people’s daylight, bounced back at you from around the world [2][3].

3. Aurora and lightning from the ISS

Sometimes a change in perspective can be quite literal – as with this video of the Earth seen from the International Space Station. The green structures are aurora- the Northern Lights over Canada in this case. You can also catch the occasional flash of lightning. This time-lapse is haunting and shows you a view you could probably never otherwise see.

4. M31 compared to a full moon

m31abtpmoon

The Andromeda Galaxy is our nearest neighbouring galaxy and can be seen as a faint fuzzy patch in the Northern Sky. What is amazing though, is to realise that in fact it is quite a large object – bigger than our own Moon in our sky. Out eyes just don’t see it very well! Long-exposure images show just how big it really is. Combine this with the fact that it is 200 million light years away [4] and you begin to realise that the galaxy next door is truly enormous. It’s about the same shape, size, and type as our own Milky Way too. So we will look pretty similar to anyone looking up at the sky from a planet in the Andromeda galaxy.

5. Earth from Saturn (and other places)

PIA17172

There are perhaps no images quite as humbling and shifting as the set of images we would probably call the ‘pale blue dots’. These are the small set of mages of the Earth from far, far away taken by the robots we have sent out into the Solar System. Voyager 1 took one in 1990 from 4.7 billion light years away; Cassini has taken more than one from the Saturnian system (like the one above); a few have been taken from Mars too. All of them show the Earth as just a pixel or so across: encompassing all of humanity, the world, and all life as we know it into a teeny tiny speck against the cosmos.

6. Orion’s Proplyds

Orion_Nebula_proplyd_atlas

These dark blobs hidden within the star-forming complex of the Orion nebula are known as proplyds – or protoplanetary disks. These are embryonic solar systems in the making. Each of these blobs is far larger than our own Solar System (they get smaller as they evolve into spinning orbits) which gives you some idea as to how large the Orion Nebula is in total. We were once shrouded in such a dusty blob ourselves – though long before the Earth formed.

7. The Sloan Great Wall

SUTU_59

The largest surveys of galaxies reveal a structure in the Universe so vast that is practically beyond comprehension – but let’s try anyway shall we? The Sloan Great Wall is a filament of galaxies, snaking through the Universe that appear to be physically connected to each other – bound by gravity. The ‘wall’ is 1.38 billion light years across. That’s 1/67th of the observable Universe! When light is emitted on one side it doesn’t reach the other end for 1.38 billion years. It is 1,600 times a long as the distance between the Milky Way and Andromeda. I told you it was hard to imagine.

8. Apollo 8 on Christmas Eve 1968

AS8-14-2383HR

I thought it would be good to end on something a little closer to home. On December 24th 1968 astronauts Bill Anders, Jim Lovell, and Frank Borman were the voices heard on one of the most-watched television broadcast of all time. As they read passages from the Bible’s Book of Genesis, they broadcast a grainy image of the Earth, as seen from the orbit of the Moon. The world watched themselves from space for the first time, and saw the Earth as a singular marble, set against the deep black of space. The image has since been remastered and still represents an era, and a moment in human history, that many find totally perspective changing. A symbol of a race of beings from a tiny planet, venturing outward to explore space and the worlds beyond their own. Remarkable.


[1] I recently had my first go at some proper astrophotography from a dark site. My target was the Milky Way and the result was this image of the dust lanes of our galaxy toward the centre of the galaxy. I’m pretty happy with it for a first go.

[2] This effect can also be seen on other moons around other planets and is generically called ‘Planetshine‘.

[3] This also serves as a good reminder that there is a part of the Moon we never see – the far side – which is lit by the Sun, but just never seen from Earth.

[4] That distance gets smaller all the time, and Andromeda will actually collide with us in about 4 billion years.

That’s No Supermoon

June 24, 2013 — 4 Comments

The periodic mention of a ‘supermoon‘ in the news cycle is starting to annoy me. A supermoon is simply not that much bigger than any other Moon!  It’s apparently just perceptible but by no means would you call it ‘super’. Annoyingly though, observation of the so-called supermoon is wrapped up in another effect: the Moon Illusion. This means that people enthusiastically report seeing a really big Moon, but don’t realize that they would likely have thought it big on any other Full Moon night too.

So let me put my rant in some context. The term supermoon was coined by astrologer Richard Nolle about 30 years ago. It refers to a Full Moon or New Moon that occurs when the Moon is in the closest part of its orbit around the Earth. The Moon’s orbit is not perfectly circular and there is a closest point in every cycle (perigee) and a most-distant point too (apogee). At perigee the Moon is closer to the Earth by about 50,000 km (30,000 miles), which is enough to make the Moon appear slightly larger in the night sky. In fact it is about 1.1 times larger in it’s angular diameter on the sky. Expert Moon watchers can see a subtle difference but it’s pretty slight and hardly warrants the title of a ‘super’ moon.

The Moon's motion over one cycle.

The Moon going through one complete orbit as seen from the Earth.

This animated GIF shows a Moon going through one entire orbit (apogee-perigee-apogee) and you can see the changing size (you can also see it undergoing libration, which is the wobbling motion). You can a direct size comparison below. In both these cases you’re seeing it close-up – imaging these things hanging in the sky at a distance. The size change is happening in every cycle, but is most prominent when the Full Moon coincides with perigee, as was the case this week.

Size Comparison for the Moon at Apogee and Perigee

Size Comparison for the Moon at Apogee and Perigee [Source: http://www.fourmilab.ch/earthview/moon_ap_per.html%5D

So there is a difference in the appearance of the Moon but it is very small and you’re unlikely to be seeing this when you go outside to look at a supermoon. What you’re actually experiencing is most likely the Moon Illusion: the optical illusion that the Moon looks larger when it is near the horizon than when it is high in the sky. The Moon Illusion is not well understood but most astronomers are very familiar with it. It may be partially caused by the Ebbinghaus illusion, which is the one that makes the two central circles in the following image appear to be different sizes when they are, of course, the same. When close to the horizon the Moon is compared to objects like rooftops, hills and clouds. When high in the sky is mostly seen in wide-open space. Another explanation may lie in the processes that govern our binocular vision; it might be that the Moon Illusion does not occur of you stand on your head, for example. This has not (yet) been tested widely.

Ebbinghaus Illusion

So what happened over the weekend was that people heard about a supermoon and so went outside to see it. Given that it any observable supermoon is a Full Moon, this means people went out to see it when it was low down in the sky, because Full Moon’s rise late in the evening. Thus they probably experienced the Moon Illusion and reported that indeed the Moon looked very large.

On a final point: the supermoon is also given silly superpowers by some new outlets too. The natural oscillation of the Moon’s distance does indeed affect tides a little, but it does not cause earthquakes, madness or werewolves.