Tag Archives: astronomy

Uncharted territory: how big is the universe?

How far is too far? On groggy Sunday mornings, the gym may seem “too far”, while for two long-distance lovers separated by circumstances, they are always “close enough”. For some, distance is relative to our motivation. Space, however, does not care what you think.

Voyager 1. Image from NASA.

It’s been over 35 years since NASA’s launch of Voyager 1, and since then, it has travelled almost 20 trillion kilometers from home. You might think that that’s far, but in the grand scheme of the universe where distances are measured with respect to light, it has travelled a mere 18 light-hours. To put that into perspective, the nearest star to our Sun, Proxima Centauri, is about 4.24 light-years away.

So how big is the universe then?

Before we address that, we need to know how old the universe is. Based on measurements of the cosmic microwave background, which is basically leftover radiation from the Big Bang, astronomers are confident that the universe is about 13.8 billion years old. Since Distance = Velocity × Time and nothing can travel faster than light (?), the universe must have a radius of 13.8 billion light-years, right? Wrong!

The Doppler effect on the pink sound waves. Image from user Charly Whisky from Wikipedia.

The short answer to the size of the universe is that it is at least 93 billion light-years in diameter. The reason that the universe is larger expected is because the universe is expanding. This can be determined by the apparent redshift of distant stars due to the Doppler Effect. So an object emitting light from 13.8 light-years away would have moved to a position much farther away.

One thing to note, is that this measurement is only what we can observe.  The observable universe from another planet billions of light-years away is likely different from our reference frame of the Earth. Is the universe infinite? Perhaps. But for now, we can appreciate that even though our paradigm of the universe is limited, there is still much to explore; we have observed billions of galaxies, and in each are billions of stars, each hosting their own worlds much like ours. Despite the uncertainty in the true size of the universe, we know that space is vast. As the Dutch artist Vincent van Gogh had once said, “for my part I know nothing with any certainty, but the sight of the stars makes me dream.”

If you have 45 minutes to spend exploring part of our Solar System, check out Alphonse Swinehart’s video below, where you travel from the Sun to Jupiter at the speed of a photon! Do yourself a favour and enjoy the video in full screen mode.

– Trevor Tsang


“The Dark Side of the Moon” – What happened to the moon last Sunday?

Last Sunday, half of the world bore witness to a rare event that had not occurred in over 30 years, and will not occur again for more than 15. Two fairly common events coincided on the same night: a lunar eclipse and a “supermoon”.

For  civilizations living centuries before us without technology like telescopes to help explain why, the sight of a lunar eclipse inspired many interesting theories to try to explain the frightening but captivating occurrence. These stories often involved some sort of celestial conflict or consumption of the Moon. Nevertheless, our faithful heavenly body never failed to rise again on the following night.


Progression of the “supermoon eclipse” on September 27, 2015. Source: Peter Martin Jørgensen from flickr.

Today, we know that a lunar eclipse, also eerily known as a “blood moon” for its red colour, happens when the Moon is in the shadow of the Earth. The Moon itself does not generate its own light like the Sun does, but rather, reflects the Sun’s light. During an eclipse, the Earth is between the Sun and the Moon, preventing the Sun from fully illuminating the Moon. The reddish tinge is a result of certain wavelengths of the visible light being scattered by the Earth’s atmosphere, much like why a sunset appears red.

There are two types of lunar eclipses: penumbral and umbral. How illuminated the Moon is during an eclipse depends on what part of Earth’s shadow its orbit crosses. An umbral lunar eclipse occurs when the Moon crosses into the Earth’s inner shadow, or umbra. These eclipses do not allow much light to reach the Moon. On the other hand, penumbral lunar eclipses occur when the Moon crosses into the Earth’s wider, outer shadow, called the penumbra. Penumbral lunar eclipses are less noticeable than umbral ones, but are more common, happening several times a year.

Geometry of a lunar eclipse. Source: User Sagredo from Wikipedia Commons.


Just like how the Earth’s orbit is not a perfect circle with the Sun exactly in the centre, the Moon’s orbit is elliptical and slightly off centre. This means that at any given point in the Moon’s orbit, the distance between the two bodies varies. When the Moon is at the farthest point from the Earth, it is called the apogee. At this point, the Moon will appear smaller than usual. Conversely, the point at which the Moon is closest to the Earth is called the perigee. Colloquially known as a “supermoon”, the Moon will appear to be larger than usual. Supermoons occur four to six times a year.

Lunar perigee and apogee. Source: User Tomruen from Wikipedia Commons.

Did you miss it? Fear not: here’s a time lapse of the event from the Associated Press.

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While these celestial events no longer inspire the fear that our ancestors felt, the sense of wonder and awe still remains. The next supermoon eclipse won’t be until the year 2033. Until then, mark your calendars!

– Trevor Tsang