Alan Willison, chairman of Hertford Astronomy Group, continues his guide to getting started in astronomy - this time explaining what light years are and all about supernovas.
Bring me sunshine!
One of the most challenging concepts to get around with astronomy is distance. In our everyday lives we are used to seeing things as they are happening.
The moment we step off our planet things seem to change. For example, it takes about 1.25 seconds for a radio signal to reach the Moon. This was noticeable when we first visited the Moon in 1969 and we could tell that there was a bit of a lag between the communications as we would hear the response to a question taking about 2.5 seconds (there and back).
Radio waves travel at the speed of light so we are actually seeing the Moon as it was 1.25 seconds ago. Nothing there for us to worry about as it doesn’t really matter to us here on Earth unless you are guiding something at or on the Moon.
Light from the Sun takes about eight minutes to get here so that helps us to understand the relationship between the distances of the Moon and Sun to Earth.
Now we can build up a mental image of what a light hour might look like – about four return journeys to the Sun.
And a light day would be around 80 similar journeys.
Keep going and you can construct a light week, a light month, and eventually a light year – which is over 4,500 such journeys.
So, how far is it to the next star in our galaxy?
Proxima Centauri has the honour of being that star and it is about 4.25 light years away from our Sun.
After the three stars in the Centauri, the next star is about six light years away and that’s called Barnard’s Star, named after the chap who discovered it – Edward Emerson Barnard in 1916. Clearly, it isn’t a very bright star otherwise it would have been known about a lot earlier.
OK, so how far is it from one side of our galaxy, the Milky Way, to the other side? Well, we don’t know for certain but 100,000 light years seems to be an accepted figure.
There are millions of other galaxies out there and the nearest one to the Milky Way is the Andromeda Galaxy at 2.5 million light years away. That means that we are seeing it as it was all those years ago.
And if anyone living in the Andromeda galaxy could see Earth they could be seeing Homo habilis, which means "handy man" – an extinct species of early humans that lived around 2.5 to 1.4 million years ago in Africa.
They are considered one of the earliest members of the Homo genus, which includes modern humans (Homo sapiens) and their closest ancestors. And no, I hadn’t heard of them before now either.
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Back to our Sun, especially now that we are feeling its presence a little more. As we have mentioned in previous articles, stars have a life – they are born, they have an existence and they die.
How they die depends on what type of star they are. When stars die, they don’t always go out with a bang.
Depending on their mass and the speed of their death, stars can end their lives in a variety of ways.
Stars that are less than eight times the mass of our Sun will eventually become white dwarfs, while more massive stars may become neutron stars or even black holes.
Some stars – particularly those larger than eight solar masses – may even explode in a supernova, leaving behind a nova remnant.
Red dwarf stars are among the longest-lived and most common type of star in the universe, but they too will eventually die in a relatively quiet way.
Recently there has been some excitement in the astronomy community as a star has been spotted as it has become a supernova.
What makes it even more exciting is that it is not in our galaxy but in one 21 million light years away.
One of our own local astronomers, Steve Heliczer, managed to image it. You can sense his excitement in this report:
“Supernova!
"I captured this picture of the closest supernova in over a decade from my back garden in Cuffley. 2023ixf is located within the Pinwheel Galaxy M101, 21 million light-years away.
"This means that when I took this image this Friday (May 26), this short lasting event actually occurred over 21 million years ago!
"A supernova is a powerful and luminous explosion and occurs during the last evolutionary stages of a super-massive star or when a white dwarf is triggered into runaway nuclear fusion. The original star either collapses to form a neutron star or black hole, or is completely destroyed to form a diffuse nebula.
"The peak optical luminosity of a supernova is often comparable to that of the entire galaxy before fading over several weeks.
"This single star from this distant galaxy appears as bright as many stars in our own galaxy a few hundred light years away.
"The forces involved in these super massive "explosions" produce the heavier elements that occur in the periodic table.
"A similar supernova happened in our own galaxy which created the heavy elements, some of which were required to create life on Earth.
"If you have a telescope or a good pair of binoculars, this event will be visible for the next week or so. Being able to see a single star within another galaxy is an extremely rare event.”
Steve’s images show the supernova as that bright star and the negative image show just exactly where it is – the bright one at the bottom of the spiral.
First discovered by Koichi Itagaki on May 19, Steve’s picture was taken on May 26 – just seven days after the discovery.
Will this happen to our own Sun?
Our Sun is currently in the middle of its main-sequence phase, during which it is converting hydrogen into helium in its core. Eventually, in approximately 5 billion years, our Sun will exhaust its supply of hydrogen and begin to evolve off the main-sequence so no immediate need for panic.
The Sun will start to become a red giant star, expanding so that its outer layers encompass Mercury and Venus. In this phase, it will start to convert helium into carbon and oxygen.
Eventually, the Sun will reach a point where it has too little mass to continue fusion reactions in its core. At this point, it will become a white dwarf.
At the moment the Sun is approaching its peak in sunspot activity. Sunspots are dark spots that appear on the surface of the sun. They are an indication of solar activity and can be used to predict solar cycles.
Sunspot activity is closely monitored by scientists due to its role in predicting space weather events, such as solar flares and coronal mass ejections. Additionally, sunspots have been linked to climate change on Earth, making them a valuable tool for understanding our planet's climate history.
Our Picture of the Month by Michal Naczynski (https://www.instagram.com/michal.astro.diary/) shows solar activity. You can see sun spots and solar prominences.
A solar prominence is an amazing phenomenon in our solar system, and it's quickly becoming a hot topic of conversation.
From scientists to everyday people, everyone wants to know more about this fascinating occurrence.
Solar prominences are huge loops of gas that form in the atmosphere of the Sun and can be seen from Earth with the help of powerful specially adapted telescopes.
They often appear as bright arcs or loops that can last for days or even weeks, making them an exciting spectacle to observe.
WARNING: NEVER LOOK AT THE SUN WITH A TELESCOPE OR BINOCULARS – IT CAN CAUSE PERMANENT BLINDNESS.
Would you like to learn more about the Sun?
You are welcome to come along to the next meeting of the Hertford Astronomy Group, which is meeting on Wednesday, June 14 where Dr Helen Mason will be telling us about our own Sun and how we are monitoring what it is doing.
You can join us either live at the University of Hertfordshire, College Road, Hatfield, or on Zoom to your own room. You don’t have to be a member to take part.
Details and tickets can be found at: https://hertsastro.org.uk
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