# What will be the temperature on Earth when Sun finishes its main sequence?

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We know that presently Sun is 4.5 billion years into its main sequence. It has another 5 billion years before it enters the Red Giant phase. We also know that Sun's luminosity increases by 10% every billion years during the main sequence. I am interested in finding the temperature rise as we approach the end of main sequence. I got two different values for temperature on Earth.

Wikipedia entry says that temperature on Earth would be 422 k in 2.8 billion years. However, if we use the formula for effective temperature as discussed in this answer https://earthscience.stackexchange.com/a/4274/15299 and L = 1.8 then, the temperature on Earth would be 330K. Also in this book, the author does the same calculations on page 255.

The difference is that your analysis is assuming that the albedo stays fixed, so the surface temperature simply scales like luminosity to the 1/4 power. The Wiki entry is including feedback from the greenhouse effect, which will tend to further increase the surface temperature. Note that an analysis that just looks at solar irradiation would get way too low a surface temperature for Venus, for example. I can't speak to the accuracy of the feedback included-- as I understand it, that is far from a simple effect to include.

## Sun and moon anomally

Below is a photo that my son took in Scotland showing the sun and moon at the same time. I immediately noticed this anomaly that the light illuminating the moon could not possibly come from the sun. I sent the photo to 4 University astronomy departments and only one responded and that was Cambridge University which is near where I live. The response came from the department librarian (not an astronomer) who said he had never heard of this before. He gave me two possible solutions, one was was from an engineer (not an astronomer) in which he got confused between perspective and light ray tracing and the other was referring to Einstein's theory of light bending by gravity. I check out Einstein and the effect was so small as to be almost immeasurable.

I have looked at the various 'complex' explanations for what to me is a very simple model. What need is there to introduce 'curved planes' and 'starry sky domes' all of which do not exist in reality? It is only referred to as an 'illusion' because observation doesn't fit the conventional model hence the complex explanations to try and make it work. The anomaly is acknowledged to exist with or without photos. Since everyone believes that the moon is illuminated by the sun then simple normal physics do not seem to work. Either the physics is wrong or the sun does not illuminate the moon. I realise that is a heavy statement!

Therefore I state once again:

1. The sun and the moon are two objects (like a torch and a football) that are suspended in a 3 dimensional space and size should not matter.
2. The moon/football are illuminated by the sun/torch and a perpendicular line or light ray can be drawn between them.
3. It doesn't matter where in space you choose to view them, a perpendicular line or light ray can still be drawn between them.

This drawing explains my doubts:

I'm very surprised that some of you have never noticed it before hence the suggestion asking me to post a video. This is a very common occurrence and I have seen it many many times as I go for my morning walk at about 8.00am every morning. I have never thought of actually tabulating my observations.

## What will be the temperature on Earth when Sun finishes its main sequence? - Astronomy

Hi I am a novelist from Norway and I have some questions concerning the death of the sun.
My questions:
If the Sun became a red giant will the Earth still be able to support life here?

Jagadheep: No, the Earth will not be able to support life if the Sun becomes a giant star. Giant stars have large radii as their name implies. When the Sun becomes a giant star, it may become so large as to engulf Earth, in which case the planet will be destroyed. Even if this does not happen, the sun will expand so far out that the temperatures on Earth will become extremely high so that all oceans will evaporate away, and there will be no water left on Earth. So, no life which depends on water will be able to survive.

When the sun starts expanding in about 5 billion years, what will be the first signs of this process?

Karen: The Sun is a relatively low mass star and as such its death will be relatively mundane (at least by Astronomical standards). The Sun's luminosity and radius have been increasing since it started life and will continue to gradually increase in this manner for another 4.5 billion years or so. When the hydrogen in the core is all used up energy generation will stop there, however it will continue in a thin shell around the core. It is this which makes the Sun expand since it heats up the outer layers more. Funnilly enough this makes the very outer layer cooler so that sun will actually redden as well as becoming brighter and expanding. I suspect that this reddening might be the first signs the the Sun has left the Main Sequence.

How long will it take from the process starts til the earth is engulfed, or at least uninhabitable?

Timescales are difficult in evolutionary models of stars. It's not clear quite what'll happen to the Earth either. It could be engulfed by the Sun, or it might get pushed out into a larger orbit and freeze as the Sun expands. The Sun will be a Red Giant for a few million years. By then I think it's safe to say that the Earth will be uninhabitable.

Will the earth catch fire while humans still live here or will the planet simply dry out?

I think that the temperature would kill life before anything caught on fire. It would only need to be 100F or so all the time for humans to be wiped out (we don't survive long in the desert, right).

Is it probable that life on earth will survive that long, or will asteroids wipe us out before then?

Probability wise, it's likely that the Human Race will have been killed off by the time the Sun leaves the Main Sequence. I don't think that any species in history has dominated the Earth for that long. Of course we could be the first.

Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy. These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow. Jagadheep is currently at the Indian Institute of Space Scence and Technology.

## Star in a Box: High School

The accuracy of their answers to the question can form the basis of the evaluation of students’ understanding. However, more detailed feedback can be obtained by talking to individual students about their understanding.
- Ask students to talk through what is happening to a 1 solar mass star as the star marker moves around the graph.
- Ask students why different initial masses of star lead different life cycles what are the main differences and happens at the end of these stars lives?

• Students should understand what a star is in broad terms before starting this activity.
• Students should be familiar with the concept of hydrogen burning/fusion.
• Students should be familiar with using graphs to display and discern information.
• Teachers can use the Powerpoint presentation provided to give students a full lesson about the life cycle of stars before attempting the activity (available at http://lco.global/education/starinabox).

Star in a Box app is available at http://starinabox.lco.global

### Step1

• Open the lid of your ‘Star in a Box’.
• The graph is a Hertzsprung-Russell diagram, where a star’s luminosity is plotted against its temperature.
• The information panels allow you to compare the Sun with your star. It compares the relative radius, surface temperature, brightness (luminosity) and mass of the star to the Sun.

### Step2

#### The Sun’s Evolution during its lifetime.

Click the play button below the Hertzsprung-Russell diagram to show the Sun’s evolution.

Name the three stages of the Sun’s life shown on the Hertzsprung-Russell diagram.

Use the table below to describe the changes the Sun will go through between stages.

• Label ‘Increase’, ‘Decrease’ or ‘Stay the same’ for each of the quantities in the table along with the values they change from and to.

Look at the light bulb tab:

• At which stage in its life cycle will the Sun be at its brightest?
• How old will the Sun be at this point? Myr

Look at the thermometer tab:

• At which stage in its lifecycle will the Sun be at its hottest?
• What is its maximum temperature? K

Look at the pie chart tab:

• In which stage of its life will the Sun spend most of its time?
• How long will it spend in this stage? Myr

What type of star will the Sun be at the end of its life?

What is the total lifetime of the Sun?

### Step3

#### Using the ‘Star Properties’ banner, explore the evolution of stars with different starting masses.

• Select a different starting mass for your star in the ‘Star Properties’ banner.
• Using the Hertzsprung-Russell diagram tab, click play to watch your new stars evolution.

Try out a few different masses then answer the following questions.

Using the Hertzsprung-Russell diagram:

Where on the main sequence do the higher mass stars start?

There are three possible outcomes for the final stage of a stars life depending on its initial mass. Name these 3 possible final stages.

### Step4

#### Follow the evolution of five stars of different masses.

Complete the table below, filling in a row for each of the different masses.
Hint: You may find it easier to use the data table on the ‘Star in a Box’ to find the exact values.

Mass of Star (Msun) Maximum Radius (Rsun) Maximum Luminosity (Lsun)(Brightness) Maximum Temperature (K) Name of Final Stage Total Lifespan (Myr)
0.2
1
6
20
40

### Step5

#### Study the data for the different stars in your table above.

Comparing the temperatures:

• Which mass star reaches the highest temperature?
• At what stage in its life does the star reach this temperature?

Comparing the luminosities:

• Which mass star gets the most luminous (brightest)?
• Is this the same mass of star that reaches the highest temperature?

### Step6

#### Multiple choice questions. Choose the correct answer.

What type of star will the Sun become after it leaves the Main Sequence?

What main factor determines the stages a star will follow after the main sequence?

The mass of the star Betelgeuse is much greater than the mass of the Sun therefore, its total lifetime will be:

Compared to when it joins the Main Sequence, a star’s mass at the end of its life will:

The Sun will spend most of its life in what stage?

Country Level Subject Exam Board Section
UK GCSE Physics AQA Science A Not in current curriculum
UK GCSE Physics Edexcel P1.3: 11, 12, 13
UK GCSE Physics OCR A P7.3.8 P7.4: 22-28
UK GCSE Physics OCR B P2h
UK GCSE Physics WJEC Physics 3.5: b, c, d, g, j
UK GCSE Astrophysics Edexcel Unit 1.3: 3o-q, 4a, 4c
UK A level Physics AQA 3.9.2.5
UK A level Physics Edexcel Topic 10: 159, 160
UK A level Physics OCR A 5.5.1: c, e, g
UK A level Physics OCR B 5.1.3: b, c
UK A level Physics WJEC Unit 1 6d)
UK KS3 Physics - Space Physics: Our Sun as a Star
UK KS2: Year 5 Science - Earth and Space
• If you would like to know more about how stars evolve, take a look at our SpaceBook pages about the life cycle of stars. http://lco.global/book/life-cycle-stars
• Questions in the exercise workbook could be made into a multiple choice quiz using a website or an app such as Socrative https://itunes.apple.com/au/app/teacher-clicker-socrative/id477620120?mt=8.

#### Language version:

The Spanish version of &ldquoStar in a Box: High School&rdquo translated by Mariana Lanzara, proofread by Pau Ramos and reviewed by Dr. Amelia Ortiz-Gil for the Astronomy Translation Network project. Download the files: http://astroedu.iau.org/media/files/Spanish_Star_in_a_Box_Highschool.zip

The activity finishes when the students have completed the worksheets. The teacher should discuss the range of answers the students had for some of the later questions on each worksheet.

## Earth's orbit and historical sun-earth distance

Purpose of my question: I create program to calculate solar radiation and I need to calculate radius between sun and earth.

The based on book "Guide to HTML, JavaScript and PHP" For Scientists and Engineers, By David R. Brooks. The code is derived from this link which is a calculator. I edited the code to C.

In my code the radius calculation is defined as o->R =1.000001018*(1.0-e*e)/(1.0+e*cos(f)) where e - eccentricity of the earth's orbit: f- true anomaly of the sun:

This is function to calculate solar position. It works exactly the same as Bird and Hulstrom's Solar Irradiance Model refered the calculator (see link above). Here I use i input object where input data are are saved and o ouput object where the calculated data regarding solar position are saved after they are calculated. atan2 - Returns the principal value of the arc tangent of y/x, expressed in radians (whatever it means, this is taken from C/C++ manual -

). Ceil rounds up floor rounds down.

The problem is that if I set old date like 1849/06/31 11:15 The Solar constant corrected to Radius does not fit the historical records. In the case the result would 1322.3 be for SolConst 1367. Which is crazy. According historical data it should be 1361.035. So I expect the radius is wrong calculated.

Earth/Sun distance correction is made in another function to calculate solar radiation. The code:

1) where can I get historical records of the sun-earth radius

2) what is wrong with this formula or this calculation? Can you suggest better formula?

Edit: I add the code needed to calculate radiation and solar constant correction.

## Becoming a Giant Again

After the helium flash, the star, having survived the “energy crisis” that followed the end of the main-sequence stage and the exhaustion of the hydrogen fuel at its center, finds its balance again. As the star readjusts to the release of energy from the triple-alpha process in its core, its internal structure changes once more: its surface temperature increases and its overall luminosity decreases. The point that represents the star on the H–R diagram thus moves to a new position to the left of and somewhat below its place as a red giant (Figure 1). The star then continues to fuse the helium in its core for a while, returning to the kind of equilibrium between pressure and gravity that characterized the main-sequence stage. During this time, a newly formed carbon nucleus at the center of the star can sometimes be joined by another helium nucleus to produce a nucleus of oxygen—another building block of life.

Figure 1. Evolution of a Star Like the Sun on an H–R Diagram: Each stage in the star’s life is labeled. (a) The star evolves from the main sequence to be a red giant, decreasing in surface temperature and increasing in luminosity. (b) A helium flash occurs, leading to a readjustment of the star’s internal structure and to (c) a brief period of stability during which helium is fused to carbon and oxygen in the core (in the process the star becomes hotter and less luminous than it was as a red giant). (d) After the central helium is exhausted, the star becomes a giant again and moves to higher luminosity and lower temperature. By this time, however, the star has exhausted its inner resources and will soon begin to die. Where the evolutionary track becomes a dashed line, the changes are so rapid that they are difficult to model.

However, at a temperature of 100 million K, the inner core is converting its helium fuel or carbon (and a bit of oxygen) at a rapid rate. Thus, the new period of stability cannot last very long: it is far shorter than the main-sequence stage. Soon, all the helium hot enough for fusion will be used up, just like the hot hydrogen that was used up earlier in the star’s evolution. Once again, the inner core will not be able to generate energy via fusion. Once more, gravity will take over, and the core will start to shrink again. We can think of stellar evolution as a story of a constant struggle against gravitational collapse. A star can avoid collapsing as long as it can tap energy sources, but once any particular fuel is used up, it starts to collapse again.

The star’s situation is analogous to the end of the main-sequence stage (when the central hydrogen got used up), but the star now has a somewhat more complicated structure. Again, the star’s core begins to collapse under its own weight. Heat released by the shrinking of the carbon and oxygen core flows into a shell of helium just above the core. This helium, which had not been hot enough for fusion into carbon earlier, is heated just enough for fusion to begin and to generate a new flow of energy.

Farther out in the star, there is also a shell where fresh hydrogen has been heated enough to fuse helium. The star now has a multi-layered structure like an onion: a carbon-oxygen core, surrounded by a shell of helium fusion, a layer of helium, a shell of hydrogen fusion, and finally, the extended outer layers of the star (see Figure 2). As energy flows outward from the two fusion shells, once again the outer regions of the star begin to expand. Its brief period of stability is over the star moves back to the red-giant domain on the H–R diagram for a short time (see Figure 1). But this is a brief and final burst of glory.

Figure 2. Layers inside a Low-Mass Star before Death: Here we see the layers inside a star with an initial mass that is less than twice the mass of the Sun. These include, from the center outward, the carbon-oxygen core, a layer of helium hot enough to fuse, a layer of cooler helium, a layer of hydrogen hot enough to fuse, and then cooler hydrogen beyond.

Recall that the last time the star was in this predicament, helium fusion came to its rescue. The temperature at the star’s center eventually became hot enough for the product of the previous step of fusion (helium) to become the fuel for the next step (helium fusing into carbon). But the step after the fusion of helium nuclei requires a temperature so hot that the kinds of lower-mass stars (less than 2 solar masses) we are discussing simply cannot compress their cores to reach it. No further types of fusion are possible for such a star.

In a star with a mass similar to that of the Sun, the formation of a carbon-oxygen core thus marks the end of the generation of nuclear energy at the center of the star. The star must now confront the fact that its death is near. We will discuss how stars like this end their lives in The Death of Stars, but in the meantime, Table 1 summarizes the stages discussed so far in the life of a star with the same mass as that of the Sun. One thing that gives us confidence in our calculations of stellar evolution is that when we make H–R diagrams of older clusters, we actually see stars in each of the stages that we have been discussing.

## Shared Flashcard Set

Collapse of interstellar material under its own weight causes star formation.

Gravitational attraction of the dust and gas causes
the cloud to begin to condense

What two conditions must be just right for the collapse to occur?

1. The cloud must be dense enough:
• lots of mass in a given volume
• gravity is great enough to cause collapse
2. The cloud must be cold enough:
• hotter gas, higher pressure
• if gas is to hot, outward pressure can balance
gravity to stop the collapse.

7 stages of Star Formation

2. Collapsing Cloud Fragment

• tens of parsecs across
• billions particles/ m 3
• cloud fragments during collapse
• each fragment becomes a star
• dozens of stars from one cloud
• about 100 times the size of the Solar System
• initially doesn't heat much because radiation escapes
• eventually becomes dense enough to trap radiation and begins to heat up
• roughly the same size of the solar system
• inner part of cloud is opague and heats up ALOT
• center has temperature = 10,000K
• outer part still cool and thin
• center has 10 18 particles
• inner part becomes a (proto-star)
• Kelvin-Helmboltz Contraction Phase
• *Proto-star: prestellar object hot enough to emit IR, but not hot enough for fusion.
• will continue to be proto-star until fusion begins.
• core temp 1 million K
• contraction slows, but does not stop
• from stage 4 to 6 is the Hayashi Track called a T Tauri Star
• during stage 4 the star begons to appear on the H-R Diagram
• Surface Temperature: 5,000K
• Core Temperature: 5 Million K
• Contraction: still slowing
• Still a T Tauri Star, on the Hayashi Track
• Core Temperature reaches 10 million K, hot enough to start H fusion
• size is a bit larger than the sun
• surface a bit cooler than the sun
• luminosity a bit less than the sun

The Star (The Main Sequence)

• central density about 10 32 particles
• central temperature 15 million K
• surface temperature 6,000 K
• star has arrive along the zero age main sequence (ZAMS)
• left edge of main sequence is where all stars begin thie stage of life

Stage 4-6: the Hayashi Track, called T Tauri Star
Stage 6: Hydrogen Fusion in core (then quickly to 7)

## Comparison with other stars

Our Sun is quite a typical star in the Universe, and when we compare some of its features, especially its temperatures, we once again realize how vast is the world we live in.

Some of the hottest stars in the Universe may reach up to 100.000 degrees Fahrenheit as such, they are at least ten times hotter than our Sun.

But these are the estimatives of just the surface temperatures. Inside the core, temperatures are genuinely astonishing. Some stars reach about 200 million degrees inside their cores or more than eight times the Sun’s core temperatures.

There is another thing to consider when certain stars end their lives in massive explosions the inside temperatures could reach as high as 10 billion degrees.

Though these estimates are hard to fathom, we can be thankful that our Sun is among the most common types of stars in the Universe, which generally have, at least as we currently understand, the right temperatures for life to develop.

Coming back at our solar system, distance from the Sun or a star in general, doesn’t necessarily mean cooler temperatures. Take Mercury, for example.

Even though it is the closest planet to the Sun, it isn’t the hottest. Venus instead takes the first place as the hottest planet of our solar system. But this is only because Venus has an awkward atmosphere that traps heat inside.

## University of California, San Diego Physics 7 - Introduction to Astronomy

The actual process of star formation remains shrouded in mystery because stars form in dense, cold molecular clouds whose dust obscures newly formed stars from our view. For reasons which are not fully understood, but which may have to do with collisions of molecular clouds, or shockwaves passing through molecular clouds as the clouds pass through spiral structure in galaxies, or magnetic-gravitational instabilities (or, perhaps all of the above) the dense core of a molecular cloud begins to condense under its self-gravity, fragmenting into stellar mass clouds which continue to condense forming protostars. As the cloud condenses, gravitational potential energy is released - half of this released gravitational energy goes into heating the cloud, half is radiated away as thermal radiation. Because gravity is stronger near the center of the cloud (remember Fg

1/distance 2 ) the center condenses more quickly, more energy is released in the center of the cloud, and the center becomes hotter than the outer regions. As a means of tracking the stellar life-cycle we follow its path on the Hertzsprung-Russell Diagram.

## Protostar

[/caption]
A star will live the majority of its live in the main sequence phase. This is where nuclear fusion of hydrogen into helium is happening in its core, and the light pressure of this energy balances out the gravitational collapse of the star. Before a star gets into the main sequence phase, though, it spends some time as a protostar – a baby star.

Stars form when vast clouds of cold molecular hydrogen and helium collapse under mutual gravity. This collapse could have been triggered by a galaxy collision, or the shockwave of a nearby supernova. As the cloud collapses, it breaks into fragments, each of which will eventually become a star of some size.

As the cloud contracts, it begins to increase in temperature. This comes from the conversion of gravitational energy into kinetic energy. The cloud continues to heat up, and the conservation of momentum of all the different particles causes the protostar to spin.

The collapse of the cloud happens fastest at its center, where the material is at the highest density and hottest temperature. Unfortunately these objects are shrouded in dust, and impossible to see with Earth-based observatories. They can be seen in infrared telescopes though, which can pierce through the veil of dust that shrouds them.

As the collapse continues, a disk of gas forms around the protostar, and bi-polar jets blast out from the top and bottom of the star. These produce spectacular shock waves in the clouds.

An object can be considered a protostar as long as material is still falling inward. After about 100,000 years or so, the protostar stops growing and the disk of material surrounding it is destroyed by radiation. It then becomes a T Tauri star, and is visible to Earth-based telescopes.

We have written many articles about stars on Universe Today. Here’s one article about protostars, and here’s another.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

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