I‘m back! Did you miss me? Turns out that when you have ‘minor surgery’ you should listen to the ‘surgery’ bit and not so much of the ‘minor.’ I’m recovering nicely, but I’m also starting the round of Christmas relative visits with children but without husband, so posts may be irregular.
I do remember that a while ago I posted some questions about stars.
1. The Main Sequence describes how most stars spend most of their lives. It was discovered that when star brightness was plotted against colour on something called a ‘Hertzsprung-Russell Diagram’ there is a very tight cluster in a curvy diagonal line. It turns out that when a star first forms from a gas cloud and begins burning hydrogen in nuclear reactions there is a very strong relationship between the mass, or amount of hydrogen it has, and its luminosity or brightness. Which is not surprising since that brightness comes from the energy released by burning the hydrogen – more hydrogen means more energy so more brightness.
Typical stars spend most of their lives on the main sequence, until they have burnt most of their hydrogen. Then there are several paths they can take depending on their size, but most of them evolve into a giant of some type while they begin to burn helium.
2. Our sun will probably not end up as a supernova, at least not immediately. When it leaves the main sequence it will have burnt so much hydrogen that its gravity is less so it will expand greatly into a red giant, out past where the Earth is now. However the Earth will also move out because of the lower gravity. It’s uncertain whether earth will survive or not, but it certainly won’t be in a form we recognise.
As a red giant the sun will have a helium core and continue to burn hydrogen in a layer around it. Gravity will make the hydrogen burn faster than when it was in the core and make the sun brighter, however the expansion will decrease the temperature. Then the helium will begin to burn, and the outer layers will be blown off leaving a slowly cooling white dwarf.
Most white dwarfs end there, however sometimes they can pick up mass from somewhere else and explode in a Type Ia supernova.
3. Stars themselves don’t actually twinkle, it’s an atmospheric effect. We live at the bottom of a vast ocean of air, and to get to us the light from stars goes through all of it, hitting gas and dust along the way. Then there is the way that it moves and forms layers that bend the light, twinkling stars are like miniature mirages we see every night.
4. Constellations are groups of stars that are in the same general region of the sky from our vantage on earth. However ‘the sky’ is three dimensional, so they can be much closer or further away and aren’t necessarily anywhere near each other.
In addition, they aren’t always made up of stars. For example in the well-known Orion, the faintest of the three stars in the Belt is actually a double star, and the middle of the sword is actually the Orion Nebula.
5. The picture shows some Sunspots. Sunspots appear dark because the surrounding surface of the sun is so comparatively bright, if they were on their own they would be extremely bright themselves. They are enormous magnetic areas that change the currents carrying heat around the sun, so they become comparatively cold.
Sunspots typically come in pairs and act as the North and South poles of enormous magnets. They have several cycles, including the well-known 11 year cycle where they increase then slowly decrease. Because they are part of the sun’s magnetism they are linked to ‘space weather,’ which is increasingly important to satellites and communications.
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