Astronomy

How would the temperature on earth be if the sun was slightly more or less powerful?

How would the temperature on earth be if the sun was slightly more or less powerful?

The temperature on earth is around 14C celsius.

It is around 1370 W/m^2 from our sun. The earth has an albedo of around 0.3

On Tatooine (from Star Wars) i have been able to calculate it goes from 1066 W/m^2 to 2100 W/m^2 (depending if the stars eclipse each other or not). Tatooine is a desert planet with a albedo of around 0.4. How can i make a simplified function to calculate what the temperature ranges from on Tatooine?

I did read on effective temperature on wikipedia, but that is higher than the level in my physics class so i didnt understand.

In the movies they say the temperatures get quite cold at night and warm during the day, so i would expect it to go something like -10C to 40C.

We can just assume the atmosphere is the same as on earth since it is breathable for humans.

Considering as the albedo increases, the temperature should decrease with an increasing albedo.

Therefore my first attempt was

T=k(1-a)*P, where T is temp, k is a constant, a is albedo and P is w/m^2

Since the atmosphere is the same, k should be the same?

Therefore

287=k(1-0.3)*1370, solving for k gives us

k=0.3

therefore temperature on Tatooine should follow the function

f(x)=T=0.3*(1-0.4)*x-273 (to get it measured in celsius)

Where 1066<>

f(1066)=-81 and f(2100)=99

the temperature are not this extreme doe, so this wont work.

I am aware this is not an accurate science, but im taking my first physics course in high school now, so I dont understand the "proper" way of doing this. Is it completely incorrect to assume temperature is proportional to (1-a) and how much power the sun gives us, when its the same atmosphere (ish)?

If anyone wants how i found out the power the twin suns gives Tatooine i can share it here.


Don't have high enough reputation to comment, but someone should mention the Stefan-Boltzmann Law: https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

When a planet (or anything) gets warmer, the amount of radiation it emits increases with the 4th power of temperature (measured on an absolute scale like Kelvins).

A planet's temperature reaches equilibrium when it receives about as much radiation as it emits back into space.

This should give you a better approximation than the linear model.


How would the temperature on earth be if the sun was slightly more or less powerful? - Astronomy

Throughout its long history, Earth has warmed and cooled time and again. Climate has changed when the planet received more or less sunlight due to subtle shifts in its orbit, as the atmosphere or surface changed, or when the Sun&rsquos energy varied. But in the past century, another force has started to influence Earth&rsquos climate: humanity

How does this warming compare to previous changes in Earth&rsquos climate? How can we be certain that human-released greenhouse gases are causing the warming? How much more will the Earth warm? How will Earth respond? Answering these questions is perhaps the most significant scientific challenge of our time.

What is Global Warming?

Global warming is the unusually rapid increase in Earth&rsquos average surface temperature over the past century primarily due to the greenhouse gases released as people burn fossil fuels. The global average surface temperature rose 0.6 to 0.9 degrees Celsius (1.1 to 1.6° F) between 1906 and 2005, and the rate of temperature increase has nearly doubled in the last 50 years. Temperatures are certain to go up further.

Despite ups and downs from year to year, global average surface temperature is rising. By the beginning of the 21st century, Earth&rsquos temperature was roughly 0.5 degrees Celsius above the long-term (1951&ndash1980) average. (NASA figure adapted from Goddard Institute for Space Studies Surface Temperature Analysis.)

Earth&rsquos natural greenhouse effect

Earth&rsquos temperature begins with the Sun. Roughly 30 percent of incoming sunlight is reflected back into space by bright surfaces like clouds and ice. Of the remaining 70 percent, most is absorbed by the land and ocean, and the rest is absorbed by the atmosphere. The absorbed solar energy heats our planet.

As the rocks, the air, and the seas warm, they radiate &ldquoheat&rdquo energy (thermal infrared radiation). From the surface, this energy travels into the atmosphere where much of it is absorbed by water vapor and long-lived greenhouse gases such as carbon dioxide and methane.

When they absorb the energy radiating from Earth&rsquos surface, microscopic water or greenhouse gas molecules turn into tiny heaters&mdash like the bricks in a fireplace, they radiate heat even after the fire goes out. They radiate in all directions. The energy that radiates back toward Earth heats both the lower atmosphere and the surface, enhancing the heating they get from direct sunlight.

This absorption and radiation of heat by the atmosphere&mdashthe natural greenhouse effect&mdashis beneficial for life on Earth. If there were no greenhouse effect, the Earth&rsquos average surface temperature would be a very chilly -18°C (0°F) instead of the comfortable 15°C (59°F) that it is today.

See Climate and Earth&rsquos Energy Budget to read more about how sunlight fuels Earth&rsquos climate.

The enhanced greenhouse effect

What has scientists concerned now is that over the past 250 years, humans have been artificially raising the concentration of greenhouse gases in the atmosphere at an ever-increasing rate, mostly by burning fossil fuels, but also from cutting down carbon-absorbing forests. Since the Industrial Revolution began in about 1750, carbon dioxide levels have increased nearly 38 percent as of 2009 and methane levels have increased 148 percent.

Increases in concentrations of carbon dioxide (top) and methane (bottom) coincided with the start of the Industrial Revolution in about 1750. Measurements from Antarctic ice cores (green lines) combined with direct atmospheric measurements (blue lines) show the increase of both gases over time. (NASA graphs by Robert Simmon, based on data from the NOAA Paleoclimatology and Earth System Research Laboratory.)

The atmosphere today contains more greenhouse gas molecules, so more of the infrared energy emitted by the surface ends up being absorbed by the atmosphere. Since some of the extra energy from a warmer atmosphere radiates back down to the surface, Earth&rsquos surface temperature rises. By increasing the concentration of greenhouse gases, we are making Earth&rsquos atmosphere a more efficient greenhouse.


Sun's Activity Increased in Past Century, Study Confirms

The energy output from the Sun has increased significantly during the 20th century, according to a new study.

Many studies have attempted to determine whether there is an upward trend in the average magnitude of sunspots and solar flares over time, but few firm conclusions have been reached.

Now, an international team of researchers led by Ilya Usoskin of the Sodankylä Geophysical Observatory at the University of Oulu, Finland, may have the answer. They examined meteorites that had fallen to Earth over the past 240 years. By analyzing the amount of titanium 44, a radioactive isotope, the team found a significant increase in the Sun's radioactive output during the 20th century.

Over the past few decades, however, they found the solar activity has stabilized at this higher-than-historic level.

Prior research relied on measurements of certain radioactive elements within tree rings and in the ice sheets covering Greenland and Antarctica, which can be altered by terrestrial processes, not just by solar activity. The isotope measured in the new study is not affected by conditions on Earth.

The results, detailed in this week's issue of the journal Astronomy & Astrophysics Letters, "confirm that there was indeed an increase in solar activity over the last 100 years or so," Usoskin told SPACE.com.

The average global temperature at Earth's surface has risen by about 1 degree Fahrenheit since 1880. Some scientists debate whether the increase is part of a natural climate cycle or the result of greenhouse gases produced by cars and industrial processes.

The Sun's impact on climate has only recently been investigated. Recent studies show that an increase in solar output can cause short-term changes in Earth's climate, but there is no firm evidence linking solar activity with long-term climate effects.

The rise in solar activity at the beginning of the last century through the 1950s or so matches with the increase in global temperatures, Usoskin said. But the link doesn't hold up from about the 1970s to present.

"During the last few decades, the solar activity is not increasing. It has stabilized at a high level, but the Earth's climate still shows a tendency toward increasing temperatures," Usoskin explained.

He suspects even if there were a link between the Sun's activity and global climate, other factors must have dominated during the last few decades, including the increase of greenhouse gases in the atmosphere.


Holes In Sun's Corona Linked To Atmospheric Temperature Changes On Earth

Brooklyn, NY -- An unusual interdisciplinary study by astronomers and climatologists has found a striking correlation between holes in the outermost layer of the sun--or the corona--and the globally averaged temperature of the Earth, suggesting that the Earth's atmospheric temperature may be strongly linked to solar magnetism changes over months or years.

In a paper that appears in the February 28 issue of the journal New Astronomy, climatologist Eric Posmentier of Long Island University's Brooklyn Campus, solar physicists Willie Soon and Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics and physicist Pius Okeke of the University of Nigeria chart temperature anomalies seen in the Earth's lower troposphere (i.e., the region of atmosphere in which we live) using Microwave Sounding Unit (MSU) radiometers aboard weather satellites.

The scientists compared the Earth's temperature with the size of coronal holes reported on the Sun during a two-decade period, starting in January 1979 and ending April 1998. Results show a clear drop in terrestrial atmospheric temperature after the Sun's magnetic field activity is most intense. At this point, there is a dropping off of magnetic activity and an enlargement of the coronal holes. "This is the first time anyone has combined these modern, reliable data sets to link solar activity and climate, and to cite several alternative mechanisms that might explain this link," Posmentier explained.

Coronal holes are, literally, gaps in the Sun's outer atmosphere through which the stream of hot, supersonic particles known as the solar wind pours out into space to engulf the entire planetary system. At Earth, this hot bath of charged particles produces the aurorae (i.e., the aurora borealis), interferes with electrical and radio transmissions, and may threaten passengers aboard high-flying airliners or astronauts aboard unshielded spacecraft. The solar wind has also been long suspected as a possible indirect contributor to terrestrial climate change.

Posmentier and colleagues think that the connection between the solar wind and climate may be more direct, suggesting that the charged particles hitting the Earth's atmosphere may affect the properties of terrestrial water clouds, particularly the percentage of those clouds covering the Earth. In turn, significant changes in the cloud cover influence the temperature of the lower troposphere, with temperatures falling with increased cloud cover. Another possibility is that the charged particles change ozone chemistry in the upper atmosphere, in turn affecting the dynamics of the climate.

The scientists note, however, that the charged particles hitting the Earth could come from either the Sun, or from galactic cosmic rays that are modulated by the solar wind. Or, from a combination of both sources. Regardless, the percentage of the Sun's surface covered by coronal holes seems to be a fairly accurate indicator of temperature in the Earth's troposphere over months or years.

The correlation comes with some caveats. As Posmentier and colleagues note, other major climate factors are also at work concurrently, thus complicating attempts to correlate Sun-Earth phenomena. Most notable in the past two decades have been the warming effects of the 1997-98 El Nino and the general cooling that followed the eruption of Mount Pinatubo in 1991.

According to Posmentier, their results do not rule out the possible climate influence of man-made fossil fuels, which have caused the atmosphere's CO2 levels to rise. "During some parts of the last century, as the amount of CO2 increased, the temperature increased," he explained. "I don't dispute that, and I'm not saying that CO2 can't have significant effects in the future.

"What I am saying is the data do not unambiguously support the contention that CO2 increases are the dominant cause of climate variability," he added. "There are other reasons for climate variations that are significant. In fact, we've found that the strongest correlation is the one between the area of the Sun's surface covered with holes and the globally averaged temperature of the Earth."

Support for this research came from the Mount Wilson Institute and the Electric Power Research Institute, with additional funding from the Massachusetts Space Grant Consortium, the Smithsonian Institution, the Richard C. Lounsbery Foundation, and NASA.

Story Source:

Materials provided by Long Island University. Note: Content may be edited for style and length.


How would the temperature on earth be if the sun was slightly more or less powerful? - Astronomy

The seasonal temperature depends on the amount of heat received from the Sun in a given time. To hold the temperature constant, there must be a balance between the amount of heat gained and the amount radiated to space. If more heat is received than is lost, your location gets warmer if more heat is lost than is gained, your location gets cooler. What causes the amount of energy reaching a given location during the day to change throughout the year?

Two popular theories are often stated to explain the temperature differences of the seasons: 1) the different distances the Earth is from the Sun in its elliptical orbit (at perihelion the Earth is 147.1 million kilometers from the Sun and at aphelion the Earth is 152.1 million kilometers from the Sun) and 2) the tilt of the Earth's axis with respect to its orbital plane. If the first theory were true, then both the north and south hemispheres should experience the same seasons at the same time. They do not. Using the scientific method discussed in chapters 1 and 2, you can reject the distance theory.

A popular variation of the distance theory says that the part of the Earth tilted toward the Sun should be hotter than the part tilted away from the Sun because of the differences in distances. If you continue along with this line of reasoning, then you conclude that the night side of the Earth is colder than the daylight side because the night side is farther away from the Sun. This ignores the more straightforward reason that the night side is directed opposite the Sun, so the Sun's energy does not directly reach it. But let's examine the tilt-distance model a little more. The 23.5° tilt of the Earth means that the north pole is about 5080 kilometers closer than the south pole toward the end of June. This is much, much smaller than the 152 million kilometer distance between the Sun and the Earth's center at that time. The amount of energy received decreases with the square of the distance.

If you calculate (152,000,000 + 5080) 2 /(152,000,000 - 5080) 2 , you will find that the north pole would get slightly over 1/100th of one percent more energy than the south pole. This is much too small a difference to explain the large temperature differences! Even if you compare one side of the Earth with the opposite side, so you use the Earth's diameter in place of the 5080 kilometers in the calculation above, you get 3/100th of one percent difference in energy received. Clearly, distance is not the reason for the large temperature differences. Notice that I used the aphelion value for the distance between the Earth and Sun. That is because the Earth is near aphelion during the northern hemisphere's summer! This is known by measuring the apparent size of the Sun. You can safely assume that the Sun's actual size does not vary with a period that depends on the orbital period of a planet thousands of times smaller than it, or that it would choose the Earth's orbital period as its pulsation cycle.

Earth reaches perihelion in the first week of January (during the north hemisphere's winter!) and aphelion in the first week of July (during the north hemisphere's summer!). The distance theory predicts the opposite seasons from what's observed in the north hemisphere. Precise dates and times for the perihelion and aphelion events can be found at the US Naval Observatory's Applications Department's Earth's Seasons page (link will appear in a new window make the appropriate time adjustment for your time zone.)

Even though the distance model (in any variation) is incorrect, it is still a ``good'' scientific theory in that it makes testable predictions of how the temperature should change throughout the year and by how much. However, what annoys scientists, particularly astronomy professors, is ignoring those predictions and the big conflicts between predictions and what is observed. Let's take a look at a model that correctly predicts what is observed.

The tilt theory correctly explains the seasons but the reason is a little more subtle than the distance theory's explanation. Because the Earth's rotation axis is tilted, the north hemisphere will be pointed toward the Sun and will experience summer while the south hemisphere will be pointed away from the Sun and will experience winter. During the summer the sunlight strikes the ground more directly (closer to perpendicular), concentrating the Sun's energy. This concentrated energy is able to heat the surface more quickly than during the winter time when the Sun's rays hit the ground at more glancing angles, spreading out the energy.

Also, during the summer the Sun is above the horizon for a longer time so its energy has more time to heat things up than during the winter. Like baking something in the oven, the land and water do not heat up instantaneously, so our hottest days are usually after the summer solstice. That is also why the hottest part of the day is usually in the afternoon. Similarly, the coldest days are winter are usually after the winter solstice.

The Seasons module of the University of Nebraska-Lincoln's Astronomy Education program enables you to understand these concepts by manipulating such things as the position of the Earth in its orbit and your position on the Earth (link will appear in a new window---choose the third part of the module) and use their Seasons and Ecliptic Simulator in the Native Apps package (the Flash simulators no longer work with today's browsers).. You can switch between an earth-centered view showing the Earth at the center of the celestial sphere with the Sun traveling along the ecliptic and a Sun-centered view showing the Earth moving around the Sun. Both views show how the amount of daylight and the angle of sunlight upon the ground change with the passing days and the location on the Earth.

The rotational axes of most of the other planets of the solar system are also tilted with respect to their orbital planes so they undergo seasonal changes in their temperatures too. The planets Mercury, Jupiter, and Venus have very small tilts (3° or less) so the varying distance they are from the Sun may play more of a role in any seasonal temperature variations. However, of these three, only Mercury has significant differences between perihelion and aphelion. Its extremely thin atmosphere is not able to retain any of the Sun's energy. Jupiter's and Venus' orbits are very nearly circular and their atmospheres are very thick, so their temperature variations are near zero.

Mars, Saturn, and Neptune have tilts that are similar to the Earth's, but Saturn and Neptune have near zero temperature variation because of their very thick atmospheres and nearly circular orbits. Mars has large temperature changes because of its very thin atmosphere and its more eccentric orbit places its southern hemisphere closest to the Sun during its summer and farthest from the Sun during its winter. Mars' northern hemisphere has milder seasonal variation than its southern hemisphere because of this arrangement. Since planets move slowest in their orbits when they are furthest from the Sun, Mars' southern hemisphere has short, hot summers and long, cold winters.

Uranus' seasons should be the most unusual because it orbits the Sun on its side---its axis is tilted by 98 degrees! For half of the Uranian year, one hemisphere is in sunlight and the other is in the dark. For the other half of the Uranian year, the situation is reversed. The thick atmosphere of Uranus distributes the solar energy from one hemisphere to the other effectively, so the seasonal temperature changes are near zero. Pluto's axis is also tilted by a large amount (122.5 degrees), its orbit is the most elliptical of the planets, and it has an extremely thin atmosphere. But it is always so far from the Sun that it is perpetually in deep freeze (only 50 degrees above absolute zero!).


If this alien planet exists, it might be Earth-like. Or it might not.

Astronomers have found evidence for a planet orbiting a star that, if you squint a bit and don't clean your mirror too well, looks something like a reflection of the Earth and Sun.

I know, faint praise. But this is a pretty interesting planet. It's bigger than Earth, but orbits a star very much like the Sun at about the same distance Earth orbits the Sun, meaning it gets about the same amount of light Earth does. But we can't say too much about it just yet because we're missing a key piece of the puzzle — its mass.

More Bad Astronomy

If, that is, the planet exists at all.

OK, so what's what here? The star is called Kepler-160, and it's located about 3,100 light years from Earth. The star is a near-twin of the Sun: It has a little less mass and is cooler, but it's also a little bit bigger than the Sun, so the amount of energy it gives off is almost exactly the same as the Sun (it's only 1% more luminous, so very very close). It's also very old, about 9 billion years, so twice the age of the Sun.

Kepler-160 is one of 150,000 stars examined by the Kepler observatory looking for exoplanets, alien worlds orbiting other stars. If we happen to see a planet's orbit edge-on, then once per orbit it passes in front of the star, creating a transit, a mini-eclipse, and the star's light drops a tiny fraction. The amount of that dip tells us the size of the planet.

Kepler-160 was found to have two transiting planets, called Kepler160-b and c * . Both are larger than Earth and orbit the star so closely they get positively cooked by it. Earth-like they are not.

Both planets were confirmed in 2014. But new measurement techniques are dreamed up all the time, so a team of astronomers re-examined the data recently to look for more planets. They found two interesting things.

One is a possible third planet found by its gravitational influence on 160c, changing the timing of its transits. It's hard to know more about this planet since it doesn't itself transit, but they estimate it has a mass somewhere between that of Earth and Saturn (about 100 times Earth's) on an orbit that's between 7 and 50 days long, so still pretty close to the star. But that's about all that can be inferred.

Artwork depicting an exoplanet in a multi-planet system. Credit: ESA/Hubble, M. Kornmesser

But it's the fourth planet that's so interesting. They found what looks very much like a series of dips in the starlight with a period of 378 days. Applying some statistics to their measurements, they find it has an 85% chance of being real that is, not due to some instrument artifact. So they can't claim it's real — the standard is 99% confidence for a formal declaration — but the odds are good. From here on out I'll assume it's real, but just keep in mind there's a 15% chance it may not be.

So if it exists it orbits just a skosh farther from its star than Earth is from the Sun, receiving about 93% as much energy from the star as Earth does.

Known exoplanets plotted with the amount of light they receive from their star (x-axis) versus the star’s temperature (y-axis). The green region shows planets in their star’s “habitable zone”. Planet sizes are indicated by circle size solar system planets (top) are shown for scale. The possible Kepler-160 planet is arrowed. Credit: Heller et al.

But that depends on its atmosphere. Earth's average temperature without air would be about -18° C (0°F), but greenhouse gases in our atmosphere warm our average up to about 15°C (60°F). So this planet might be colder than Earth, but if it had a lot more CO2 or water vapor it could be close to our own temperature.

The problem is we have no idea what its atmosphere might be like, or if it even has one. It seems likely it will, though: The depth of the transit dip means the planet is about 1.9 times Earth's diameter, making it a super-Earth. That's about where planets start to be able to hold on to very thick atmospheres, so it could be like Earth… or it could be like Neptune. So we cannot call it Earth-like. It might be more like Venus for all we know.

This depends somewhat on the surface gravity of the planet. The astronomers estimate that if it's mostly rock and water it'll have a mass of 3.5 times Earth's, giving it a surface gravity almost exactly the same as Earth. Nifty.

But if it's metal and rock, like Earth is, the mass could be 10 – 13 times Earth's, giving it a surface gravity of 2.5 – 3.5 Earth's! That would be a bit rough. And if the planet is that dense it'll likely have a thick atmosphere. But honestly, we just don't know.

Zooming in on stars like the Sun, the Kepler-160 planet (designated KOI456.04, arrowed and plotted with uncertainty bars) can be seen to get slightly less illumination than Earth from its cooler star, and is bigger then Earth as well. Credit: Heller et al.

Still, the planet is in the star's so-called habitable zone (or HZ), where liquid water could exist on the planet's surface. We know of lots of planets in their stars' HZs, and a lot of these planets are close in size to Earth. But this occurs mostly for stars much smaller and dimmer than the Sun: red dwarfs. When it comes to stars more like the Sun, most known HZ planets are a lot bigger than Earth. This one orbiting Kepler-160 is by far the smallest (besides Earth, Venus, and Mars) for that stellar group. So that's kinda cool.

What has to happen next is the confirmation of this planet's existence. They predict the next transit will occur on 14 September, 2020. Hopefully some big ‘scopes can be trained on this star to look for it. The drop in starlight is only about 0.05%! So they'll have to look carefully. Finding its mass is much harder and could take years.

We're getting closer and closer to finding an Earth-sized planet orbiting a near-solar twin. That's no guarantee it'll be Earth-like, but still. The more of these we find, the better the odds are of finding another Earth. I think that's worth the search.

* The letter a is skipped to avoid confusion with multiple stars systems, which use a similar notation.


Not Just Another Star

Our sun is just a tiny yellow star in a vast collection that could support life. You’ll hear this more and more. Don’t believe it. The minimum requirement of a life-supporting star is missing from all the other stars. Our God-given sun appears to be unique.

Appearing bright from our perspective on earth, the sun obviously has a special status for us. But its brightness is impressive only because it lies so close compared to the stars. Given everything we now know about the brightness of other stars, it’s fashionable today to call the sun a star, even an average star. But is that really the case?

While the sun has many characteristics similar to stars, the Bible never refers to it as a star. This suggests that the sun may have some unique characteristics. Could that refer to its composition? The sun’s composition is a bit unusual—it has far less lithium than most stars do. Lithium isn’t very common in stars anyway, but the sun is among the most lithium-poor stars. Though this statistic is interesting, it isn’t clear whether it is significant.

The sun has another property that is very important and unusual—its stability. Astronomers have spent some time looking for stars similar to the sun, because such stars might be conducive to sustaining life on any planets that orbit them. Astronomers have found a few solar twins that have the same temperature, size, mass, and brightness as the sun, but nearly all of them are variable. That is, they vary in brightness. With all the concern about global warming today, it ought to be obvious that a constant sun is essential for life.

The sun may vary slightly in brightness, but it is beyond our ability to measure. So we can be confident that any normal variation is so small as to have few adverse effects on life.

In contrast to this, other stars (which are otherwise similar to the sun) typically vary in brightness by a few percent, with some varying far more. This would be disastrous for life on a planet orbiting such a star just from the standpoint of large temperature variations. Just one percent variation in the sun would result in an average temperature shift of 2°F (1°C) on earth. This may not sound like much, but this is change in the average temperature—local and seasonal changes likely would be far higher and more disruptive to life.

But there’s more than that. The variation appears to be related to magnetic activity, which can harm life. On earth we are familiar with the sun’s magnetic field because it is intimately involved with sunspots (or in the case of other stars, star spots). Every eleven years the number of spots and magnetic activity increase. During sunspot maximum the sun frequently produces energetic flares that bathe the earth in an extra dose of particle radiation that can wreak havoc on earth and damage cells in living organisms. We can only imagine how destructive the radiation would be on planets orbiting other stars.

By God’s gracious design, the earth has a protective magnetic field that prevents the sun’s flares from disrupting life. The particles racing from the sun interact with the magnetic field, which deflects most of the particles. Yet we are periodically reminded about such imminent danger when the flares overload the ability of the earth’s magnetic field to protect us. Astronauts on the Space Station must enter protected sections of the station after a solar flare.

Not all planets have strong enough magnetic fields to protect living organisms on their surfaces. Even on planets that do, the situation would be dire if the star’s magnetic activity were far higher than the sun’s. The much more frequent and far more powerful flares probably would compromise any reasonable magnetic field that a planet would have. Because this particle radiation would be harmful to living things, even secular astronomers recognize that variable stars probably can’t support living things.

Secular scientists might respond that since we haven’t observed the behavior of stars for very long, we can’t prove just how unusual the sun is with respect to its long-term stable behavior. But it’s safe to conclude that all solar-type stars vary part of the time and are stable only part of the time. We live in a time of stability, but secular astronomers have no reason to believe this has always been the case. This stability throughout life’s history on earth is easy to explain if the sun and earth are young as we creationists know, but it wouldn’t work if the sun or any star system is billions of years old.

Life requires a stable sun at all times, and that’s just what God gave us.


Contents

Mass, radius, and temperature [ edit | edit source ]

Because it was discovered by the radial velocity method, the only known physical parameter for Ross 128 b is its minimum possible mass. The planet is at least 1.35 Earth mass. This is slightly more massive than the similar and nearby Proxima Centauri b, with a minimum mass of 1.27 Earth mass. The low mass of Ross 128 b implies that it is most likely a rocky Earth-sized planet with a solid surface. However, its exact mass and radius is not known, as no transits of this planet have been observed. Ross 128 b would be 0.5 Earth radii for a pure-iron composition, and 3.0 Earth radii for a pure hydrogen-helium composition, both implausible extremes. For a more plausible Earth-like composition, the planet would need to be about 1.10 Earth radii (about 7,008 km.) With that radius, Ross 128 b would be slightly denser than Earth, due to how a rocky planet would become more compact as it increases in size. It would give the planet a gravitational pull around 10.945 m/s 2 , or about 1.12 times that of Earth.

Ross 128 b is calculated to have a temperature similar to that of Earth and potentially conducive to the development of life. The discovery team modelled the planet's potential equilibrium temperature using albedos of 0.100, 0.367, and 0.750. Albedo is the portion of light that is reflected instead of absorbed by a celestial object. With these three albedo parameters, Ross 128 b would have a Teq of either 294 K (21 °C 70 °F), 269 K (-4 °C 25 °F), or 213 K (-60 °C -76 °F). For an Earth-like albedo of 0.3, the planet would have an equilibrium temperature of 280 K (7 °C 44 °F), about 8 degrees Kelvin lower than Earth's average temperature. However, the actual temperature of Ross 128 b is currently not accurately calculable because it depends on the currently unknown atmospheric conditions, if it has any atmosphere.

Orbit and rotation [ edit | edit source ]

Ross 128 b is a closely orbiting planet, with a year (rotation period) lasting about 9.9 days. Its semi-major axis is 0.0496 AU (7.42 million km). The orbit is quite circular, with an eccentricity of 0.036, but also with a large error range as well. Compared to the Earth's average distance from the Sun of 149 million km, Ross 128 b orbits 20 times closer. At that close distance from its host star, the planet is most likely tidally locked, meaning that one side of the planet would have permanent daylight while the other side would be in permanent darkness.

Host star [ edit | edit source ]

Ross 128 b orbits the small M-dwarf Ross 128. The star is 17% the mass and 20% the radius of our own Sun. It has a temperature of 3,192 K, a luminosity of 0.00362 Solar luminosity, and an age of 9.45 ± 0.60 billion years. For comparison, the Sun has a temperature of 5,772 K and an age of 4.5 billion years, making Ross 128 half the temperature and over twice the age. The star is only 11.03 light-years away, making it one of the 20 closest stars known.


Saturn's Temperature: One Cool Planet

With an average temperature of minus 288 degrees Fahrenheit (minus 178 degrees Celsius), Saturn is a pretty cool planet. Although there are some small differences as one travels from the equator to the poles, much of Saturn's temperature variation is horizontal. This is because most of the planet's heat comes from its interior, rather than from the sun.

Layers of gas

Saturn is mostly made up of hydrogen, with some helium. Gases such as sulfur, methane, ammonia, nitrogen and oxygen lie within the planet's atmosphere, creating colorful bands.

Temperatures in Saturn's atmosphere increase along with pressure the closer one travels to the center. As a giant gas planet, Saturn doesn't have solid ground scientists set the surface of the planet at the point where pressure is equal to that of sea level on Earth.

Saturn contains three layers of clouds. The upper layers of ammonia ice have temperatures ranging from minus 280 F (minus 173 C) to minus 170 F (113 C). The next layer contains water ice, with temperatures from minus 127 F (minus 88 C) to 26 F (minus 3 C). Temperatures in the lower layers climb as high as 134 F (57 C). Pressures in this region equal those found a few miles under Earth's ocean.

When Voyager 2 traveled to the ringed planet, it found that temperatures near the north pole were about 18 F (10 C) colder than those found at mid-latitudes, a difference that may be seasonal.

Heating sources

Saturn contains a rocky core, 10 to 20 times the mass of Earth, which is surrounded by liquid metallic hydrogen. This massive core was likely the first part of the planet created, and it trapped gas as the planet formed. Moving out from the core, the liquid hydrogen becomes less metallic, gradually shifting into a gas the further one travels from the center of the planet.

The interior may reach temperatures of up to 21,000 F (11,700 C). Because the distance to Saturn from the sun averages 886 million miles (1.4 billion kilometers), most of the planet's heat comes from its core. Saturn radiates more than twice as much heat into space as it receives from the sun. Much of the heat is caused by the gravitational compression of the planet, but scientists theorize that some of it may come from friction created by helium sinking into the planet's interior.


How would the temperature on earth be if the sun was slightly more or less powerful? - Astronomy

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What causes the seasons?

Good astronomy : The seasons are mostly due to the axial tilt of the Earth. The change in distance of the Earth to the Sun is a very minor player. [ Note added January 21, 1998: This page had a math error in it when I originally published it. The error is not a huge one, and has only a small impact on the conclusions, so I simply corrected it. At the bottom of the page I include the original incorrect calculation, just to keep me honest.]

How it works : This is one of the most pernicious types of ideas: one that sounds reasonable, and so it propagates easily. Unfortunately, it's wrong. Well, not completely wrong certainly the Earth's distance from the Sun has something to do with the temperature, but it is a relatively minor effect.

First, a sanity check: The Earth's orbit is an ellipse. The Earth reaches perihelion (the point in its orbit closest to the Sun) in January, and it reaches aphelion (farthest point from the Sun) some six months later. If that were all that governed weather, we'd have summer in January, and Winter in July! This may be true for our Southern Hemisphere friends, but not up in the North. Something else must be going on.

We can check our qualitative conclusion above with some (simple!) math. The math involved in calculating a planet's gross temperature has been known for a long time. Basically, the temperature depends only weakly on distance changes the temperature goes as the inverse square root of the distance of the planet to the Sun. What does that mean? In other words, if you double the distance of a planet from the Sun, the temperature will drop by the square root of 2, or about 1.4. Doubling the Earth's distance from the Sun will drop the mean temperature by about 80 degrees Celsius (Careful here! You cannot use Celsius units for the actual calculation. You have to use the Kelvin scale, which has the same units as Celsius, but starts at 0. In other words, 0K = -273 C. If you take the square root of the temperature using Celsius you'll get the wrong answer! However, since the units are the same, an 80 degree drop is the same in both scales). Specifically, the Earth's average temperature is about 280 degrees Kelvin (10 Celsius). 280/1.4=200, or a drop of 80 degrees.

At perihelion (nearest point) the Earth/Sun distance is about 147,000,000 km, and at aphelion (farthest point) it's about 152,000,000 km. The change in temperature is then or just less than 2 percent. This turns out to be only 5 degrees Celsius, which is quite a bit less than the temperature change we see between winter and summer. Obviously, something else must be going on.

The largest contributor to the change in seasons is the tilt, or inclination, of the Earth's spin axis with respect to its orbital plane (the ecliptic ). The usual explanation is as follows: take a flashlight and a piece of paper. Shine the light straight onto the paper, so you see an illuminated circle. All the light from the flashlight is in that circle. Now slowly tilt the paper, so the circle elongates into an ellipse. All the light is still in that ellipse, but the ellipse is spread out over more paper. The density of light drops. In other words, the amount of light per square centimeter drops (the number of square centimeters increases, however, so the total amount of light stays the same-- you expect that, as the light from the flashlight has not changed).

The same is true on the Earth. When the Sun is overhead, the light is falling straight on you, and so more light (and more heat) hit each square centimeter of the ground. When the Sun is low, the light gets more spread out over the surface of the Earth, and less heat (per square centimeter!) can be absorbed. Since the Earth's axis is tilted, the Sun is higher when you are on the part of the Earth where the axis points towards the Sun, and lower on the part of the Earth where the axis points away from the Sun.

For the Northern Hemisphere, the axis points most toward the Sun in June (specifically, around June 21), and away from the Sun on December 21. This corresponds to the Winter and Summer Solstices, or the midpoints of summer and winter. For the Southern Hemisphere, this is reversed.

There is more, too. In the summer, the Sun is higher, and therefore the days are longer. This gives the Sun more time to heat the Earth, so it gets hotter. In the winter, the sun is lower, and the days are short, giving the Sun less time to heat the Earth. This is a secondary effect.

The distance of the Earth to the Sun is a smaller effect yet, but it does exist! So the Southern Hemisphere gets slightly hotter summers and slightly colder winters than the North. But only by a couple of degrees, and only on average. Your mileage may vary!

A good page about seasons can be found at The MSNBC website. They have a nice diagram (though a bit crowded) there as well.

Another one is a discussion of season misconceptions (and he takes to task the MSNBC site I mention above!).

January 21, 1998:
Okay, so I made a small mistake on the original page. I'll quote the original passage, here, and add some notes on the math as well for those of you interested in the details.

We can check our qualitative conclusion above with some (simple!) math. The math involved in calculating a planet's gross temperature has been known for a long time. Basically, the temperature depends only weakly on distance changes the temperature goes as the distance to the one-fourth power (the square root of the square root!). In other words, if you double the distance of a planet from the Sun, the temperature will drop by 2^(1/4) or 1.18. Doubling the Earth's distance from the Sun will only drop the mean temperature by about 50 degrees Celsius (the Earth's average temperature is about 310 degrees Kelvin or 10 Celsius. 310/1.18=260, a 50 degree drop. The Kelvin scale is absolute, which means it starts at 0, which is why I used it for the calculation).

At perihelion (nearest point) the Earth/Sun distance is about 146,000,000 km, and at aphelion (farthest point) it's about 152,000,000 km. The change in temperature is then or only 0.85 percent! This turns out to be only 2 degrees Celsius, which is quite a bit less than the temperature change we see between winter and summer! Obviously, something else must be going on.

My mistake was that I put in an additional factor of a square root in there, making the change in temperature a bit too small. I also used 146 million kilometers for the perihelion distance, and 147 million is actually a bit better. The temperature change from winter to summer is about 5 degrees, not 2 as I stated originally. Where I live in Washington, DC, the temperature in summer hits 35 Celsius easily, and commonly drops to 0 Celsius in the winter. 35 degrees is a lot more than 5!

To calculate the temperature of a planet, you basically need to assume that the amount of heat the planet gets from the Sun is balanced by the amount of heat radiated away by the planet. If this were not true, the planet would either heat up (if it didn't radiate the heat away) or it would freeze (if it radiates too much).

Qualitatively: the star gives off heat over its whole surface. That heat expands in a sphere centered on the Sun, and travels to the planet. The planet intersects a small piece of it which is equal to the area of a circle with the same radius as the planet (if I ever get a chance I'll place a diagram here that shows this graphically. ). The planet absorbs some of that heat, and, if it rotates quickly, re-radiates it away over its whole surface.

sigma * T planet 4 =
sigma * T Sun 4 * 4 * pi * radius Sun 2 / (4 * pi * distance 2 ) *
(1-albedo) * pi * radius planet 2 / 4 * pi * radius planet 2

where sigma is a constant (not important here, since it cancels out), T is temperature (for the planet or the Sun, each is labeled above), distance is the distance from the planet to the Sun, radius is the radius of the Sun or planet (also labeled), and albedo is a measure of the reflectivity of a planet. An albedo of 1 means the planet is a perfect reflector, like a mirror. An albedo of 0 means the planet absorbs every photon that hits it it would look black. The Earth has an albedo of 0.39, as it happens.

We can then do a bit of algebra to get:

T planet =T Sun * (radius Sun /2 * distance) 1/2 * (1-albedo) 1/4

Phew! From here you can see that the temperature of the planet depends on the inverse square root of the distance to the Sun. Note that if you put in the correct numbers for the Earth and Sun (distance=1.5 x 10 13 centimeters, T Sun =5780, radius Sun =7 x 10 10 centimeters and albedo=0.39) you get a temperature of the Earth of about 250 Kelvin. That's about -20 below Celsius, or -10 Fahrenheit! What gives?

Our atmosphere, that's what gives. Our atmosphere helps keep heat in (by absorbing some of the radiation re-radiated by the Earth), so you need a correction factor to our albedo. Without our thin layer of air, the surface temperature of the Earth would rapidly drop, freezing the oceans solid. This is called a "greenhouse effect", and is a very real occurrence. It's when things get out of control that you get a runaway greenhouse effect. Note also that the temperature on the surface of Venus should be about -20 Celsius (distance=1.1 x 10 13 centimeters, albedo=0.65 although it's closer to the Sun its albedo is higher, so it should have about the same temperature as the Earth), but is actually in excess of 500 Celsius (over 900 Fahrenheit!). Should you worry about runaway greenhouse effect? Take a look at our closest neighbor. You tell me.

My thanks to Bad Readers Darrell Bennett, Eric Carlson and Georg Zemanek for pointing out some of my errors!