Surface of the Sun, or Jupiter, etc

Surface of the Sun, or Jupiter, etc

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I keep hearing and reading statements that refer to the "surface of the Sun" (how hot the surface of the sun is) or the "surface of Jupiter" (when the Shoemaker comets hit Jupiter). I find this to be very confusing and unscientific (especially when stated by astronomers).

If the Sun and Jupiter are basically balls of gas they don't have a surface. It is like saying that the surface of the Earth is somewhere in the upper atmosphere.

Can anyone help me understand how a ball of gas can have a surface.

Yes, there is no surface in the sense as we have on the Earth.

However, there is the Barometric High/Pressure formula. It says, that in an ideal gas of atmosphere, the density (and pressure) increases exponentially high the decrease of the height. Its cause is understable even without differentiation: all horizontal layers of the atmosphere holds the mass of all the layers over it.

The result is, that in the atmosphere of the Earth, it is a good estimation of the pressure, that it halves with every $approx$ 5km of height. Thus, 5km height we have about half of our surface atmosphere density, 10km heigh we have about a fourth, and so on.

In gas planets or stars, where the whole body is gaseous, this barometric formula holds only until the gas loses its ideality, i.e. its density does not grow more linearly with the pressure. In layman terms, it means that its molecules are so close to each other, that doubling the pressure does not halve the volume any more.

This happens typically in very high pressures (some thousand bars). At this point, the gas is already so dense, that we can say, we are already "inside of the body". If the gas is radiating (for example, the thermal radiation due to the $approx$ 6000K temperature of the Sun), it also means that it is not transparent any more, thus we can not see inside it.

While there is no surface on the Sun (Jupiter, etc), the height difference between the near-total vacuum, and between the point where the atmosphere is not an ideal gas any more, is surprisingly small because of the exponentiality of the barometric formula. For example, the photosphere of the Sun, is only about some hundreds of km high. This is the layer,

  • Which is not enough dense to be able to fade the region below it;
  • But it is already enough dense to be its light enough well visible.

While there is no solid surface, this some hundreds of kms can be considered as "the surface of the Sun", particularly if we compare it to its $approx$ 1.4million km diameter.


The Astronomy ClipArt gallery offers 89 images of the tools of astronomy as well as numerous stars and constellations that can be seen in the night sky. See also the Telescopes and Binoculars ClipArt gallery.

Annual Parallax

"Suppose a to be a stationary celestial object, then as the Earth makes her annual revolution around…


"Armillary Sphere, an instrument used in astronomy. In its simplest form, consisting of a ring fixed…

Armillary Sphere

"An arrangement of rings, all circles of a single sphere, intended to show the relative positions of…


"Sir Francis Drake's Astrolabe an obsolete astronomical instrument of different forms, used for taking…


"Originally used for any instrument used for observing stars afterwards used for an instrument for…

Later Astrolabe

A historical astronomical instrument used to predict positions of the Sun, Moon, planets and stars.

Regiomontanus' Astrolabe

A historical astronomical instrument used to predict positions of the Sun, Moon, planets and stars.

Aurora Borealis

Auroras are caused by the passage of electricity through the rare air of the upper regions.

Inclination of Axis to Orbit and Ecliptic.


An improvement upon the jackstaff from Davis, the Arctic navigator.

Big Dipper

The Big Dipper is used to find the North Star.

Cause of the Phases of the Moon

During new and full moon, the earth, moon, and sun are all in the same straight line, but, that during…

Globe of Copernicus

"Copernicus, or Nicholas Koppernigk, was the founder of modern astronomy. From a school in Thorn Copernicus…

Curvature of the Earth's Surface

If the earth were flat, as soon as an object appeared on the horizon we would see the upper and lower…


Diurnal Parallax

"If we suppose a spectator placed at G, in the Earth's center, he would see the moon E, among the stars…


Earth Axis

"Now it is the inclination of the Earth's axis, as above described, which causes the lengths of the…

Earth Axis

"Now it is the inclination of the Earth's axis, as above described, which causes the lengths of the…

Earth Curvature

"The sun is so far away that it would appear at the same angle from Philadelphia, St. Louis, and Denver,…

Earth Divisions

"The Earth, whose diameter is 7,912 miles, is represented by the globe, or sphere. The straight line…

Earth Orbit

Cause of the Curved Shape of the Earth's Orbit.

Earth's Axis Perpendicular to Plane of Orbit

"The earth shown as it would be if its axis were perpendicular to the plane of the orbit." -Wiswell,…

Inclination of Earth's Axis

"A quadrant, or one fourth of a circle. The oblique lines indicate various angles with the base. The…

Spheroidal Form of the Earth

"When one is at sea, or standing on the sea-shore, the first part of a ship seen at a distance, is its…

Suns in the Equator and Ecliptic

"Were the Earth's orbit a perfect circle, and her axis perpendicular to the plane of this orbit, the…


"An Eclipse is an interception or obscuration of the light of the sun, moon, or other heavenly body…

Eclipse of the Moon

Eclipse of the Moon. S=Sun, E=Earth, M=Moon

Eclipse of the Sun

Eclipse of the Sun. S=Sun, E=Earth, M=Moon

Eclipse of the Sun

Annular eclipse of the Sun. S=Sun, E=Earth, M=Moon

Elliptical Orbit

"The elliptical circle being supposed to be the Earth's orbit, with the Sun, S, in one of the foci.…

Spring Equinox and Autumn Equinox

"Relative positions of the earth and the sun on March 21 (spring equinox) and September 21 (autumn equinox)…

Great Circle

A Great Circle is one which would be formed on the earth's surface by a plane passing through the earth's…


"The Gyroscope is an instrument constructed by M. Foucault to make the rotation of the earth visible.…


"Dollond's divided object-glass heliometer of the third type. A is the end of the reflecting telescope,…


"No part of the equatorial mounting is shown in the figure, as it resembles every respect that usual…


"The type of instrument which resulted from Russian labors. The brass tube, strengthened at the bearing…


An illustration of a heliostat or a device that tracks the movement of the sun.


An instrument used in geography to measure angles of the sun at different times of the day.


An instrument which could more readily adapt itself to the swaying of the observer's body in a sea-way,…


"Let this figure represent the Earth, N being the north pole, S the south pole, and E W the equator.…

Meridians and Parallels

The Meridian of any given place is that half of the meridian circle which passes through that place…

Meridians of Longitude

Meridians of longitude are the imaginary vertical lines that run around the Earth. These lines divide…

The big bang produced most of the helium that exists today. 75% of the mass created in the big bang was hydrogen, and the rest was almost all helium. Stars do fuse hydrogen to helium in their cores however, so some of the helium in the Sun's core is a fusion product, while some of it is primordial.

Thank you both, We read somewhere it was because of the bigbang, we just needed more information to go off of to make a correct answer. I appriciate both of you takin time out to help us.

just to add to the good responses.

The Big Bang created lot of subatomic particles (the building blocks of atoms). 300,000 years later when the universe cooled enough, those building blocks formed the smallest atoms (as you would expect). hydrogen and helium.

The observational challenges are huge - we can't take direct samples of the inside of the Sun, nor Jupiter in both cases we can only 'see' (in the optical, UV, IR, radio, etc) the 'surface' of the objects. Of course, we have samples of the solar wind (and the recently crashed Genesis satellite would have given us much more data on this!), and some info on the near Jovian environment (from Galileo), but those results need to be interpreted with caution.

So, estimates of the bulk elemental composition of these bodies relies heavily on modeling (using well-established, earthly, physics) and observational techniques such as helioseismology (and boring things like the bulk density and moments of inertia). You can also consider it to be a kind of linear programming exercise - what values of elemental abundance are consistent with the wide range of different observational and experimental results?

Surface of the Sun, or Jupiter, etc - Astronomy

Almost everything about Jupiter is a superlative. The Solar System's biggest planet also has 79 known moons, and its magnetic influence extends well over a million miles into space. It's appropriately named for the mighty king of the classical Roman gods.

  • Jupiter is nearly 143,000 km (90,000 mi) in diameter at the equator. A hollow Jupiter would have space for 1300 Earths.
  • The Sun contains nearly all of the Solar System's mass, and Jupiter has most of the remainder. If we could recycle the matter in Jupiter, we'd have enough mass to replicate the other planets, moons, dwarf planets, and asteroids, etc. In fact, we could do this twice and still have material left over.
  • Jupiter is five times farther from the Sun than Earth is, and its year is twelve Earth years long. But Jupiter doesn't have much in the way of seasons, because its axis is only slightly tilted. In contrast to Earth's seasonal changes, the amount of sunlight reaching a given latitude on Jupiter changes very little as the planet orbits the Sun.
  • Jupiter has long years, but short days. Earth takes 24 hours to rotate once, but despite its greater size, Jupiter turns so fast that its day is only ten hours long.
  • At Jupiter's distance, it's not surprising that the cloud-top temperature is a chilly -140°C (-230°F). Yet its core temperature may be around 24,000°C (43,000°F). The surface of the Sun is only about a quarter of that temperature. Jupiter emits almost as much heat energy as it receives from the Sun, a feature shared with Saturn and Neptune.

Gravity pulls on your mass to produce your weight. So you'd expect Jupiter's gravity to be impressive. Yet at the cloud-tops, it's only two and a half times Earth's gravitational pull. The pull if a body's gravity depends on its density – the amount of matter in a given volume – and your distance from its center of mass. Not only is Earth denser than Jupiter, but Jupiter's cloud-tops are a long way from its center of mass. Gravitational force drops rapidly with distance. If you double the distance, the force isn't halved, it drops to a quarter.

Beneath the clouds
But we needn't wonder how much we'd weigh on the surface of Jupiter, because Jupiter has no surface.

There's the cloud layer with its colored bands moving parallel to the equator. Beneath that, Jupiter's atmosphere is mostly hydrogen. As the depth increases, the pressure increases and the atmosphere thickens. This diagram shows that there's a deep layer of metallic hydrogen. The atoms in the metallic hydrogen state are so squashed together that hydrogen behaves like a liquid metal – it even conducts electricity. In the center of the planet, there's probably a dense rocky core with a mass of around 10-15 or more Earths.

Moons and rings
All four of the giant planets have ring systems, though none is as spectacular as Saturn's. Jupiter has three main rings, all quite faint and made mostly of dust.

Its rings may not be much, but Jupiter is rich in moons. Galileo discovered the four largest ones in 1610. By the end of 2018, 79 moons were known. Many are less than 10 km (6 miles) in diameter and were discovered in the last several decades. Of the Galilean moons, only Europa is smaller than our Moon, and Ganymede is the largest moon in the Solar System.

Observing Jupiter
When our distant ancestors observed the night sky, their eyes were drawn to this shining celestial object. With binoculars you can see the Galilean moons as points of light, and a small telescope can show the cloud bands of the planet's weather system.

Prize-winning astrophotographer Damian Peach produced this image of Jupiter and its moons Io and Ganymede. During several centuries of observing Jupiter, the widths of the white, red, brown and orange bands, and the intensity of the colors have varied. Nonetheless the general pattern of these zones (the lighter regions) and belts (the darker regions) has been been remarkably stable.

The most famous of Jupiter's features is the Great Red Spot, a giant storm with winds whirling around at 360 km/h (225 mph). It's so big you could line up three Earths across it. English scientist Robert Hooke saw a red spot as long ago as 1664. However, the first recorded observation of the current spot was in 1831, and we know It's persisted since then.

Now, in addition to ground-based telescopes, we have images from the Hubble Space Telescope and space probes. Jupiter's rings were discovered in 1979 by the Voyager spacecraft. Since 2016, NASA's Juno mission has been studying Jupiter closer than any mission before it.

An intense magnetic field
We're grateful for Earth's magnetic field. It protects us and our atmosphere from dangerous particles from the Sun. Earth's magnetosphere is puny in comparison to Jupiter's which is, on average, about 5.3 million kilometers (3.3 million miles) wide. If we could see Jupiter's magnetosphere, it would be an enormous structure in the night sky, larger than a full Moon.

Alas for Jupiter, rather than deflecting solar radiation, it traps it in deadly radiation belts. NASA's Juno mission's orbits are planned to minimize its time in the radiation belts, and the instruments had to be carefully shielded.

Content copyright © 2021 by Mona Evans. All rights reserved.
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Astronomy 1140 - Autumm 2020, MWF 11:30-12:25 PM -- ONLINE

The textbook mentioned in the syllabus is not required but recommended. In case you have it, we shall be covering Chapters 1 - 12 in the recommended textbook. However, some of those topics will not be covered in class. You should know the material we do cover in class, so read corresponding material in the textbook.

The first half of the course, up to the second quiz deals with the basic concepts in astronomy, indeed science in general. The material refers to the work by ancient Greeks (use of Geometry), through the "Dark Ages (500-1200 AD) to Copernicus (Helio-centric model - Sun is the center of the planetary system>, and on to Galileo,Tycho, and Kepler. They laid the foundation for further theoretical and observational development of astronomy (science!) through the work of Newton and up to Einstein. We shall finish the period leading up to Quiz 2 with studies of light, spectra, atoms and their inter-relationships. The Textbook covers nearly all of this, and more, but the material is spread over several chapters. Please consult the index for the material covered in class. All of the chapters and pages are not listed in the outline of the course (which is only approximate) since there is no direct correspondence.

The second half of the course is more specific in the sense that we shall mainly be studying the detailed properties of Planets. Also, there are many details (as opposed to basic laws). Most (but not all) of the topics covered in class will therefore be posted herein, as below.

The exam questions will be largely from material covered in class. The daily topics listed below cover only the main points. Make sure to read your notes and the corresponding material in the Textbook.

Dry land

It was mentioned above that Mars has almost as much dry land as does the Earth. The five largest moons of the Solar System together have more than double the Earth’s dry land. To that one might add Mercury’s 15%. Altogether, the dry, walkable surfaces of the Solar System comprises several times that of Earth. In fact, more than the total surface of the Earth, dry or not.

So while none of these places has breathable air, and they all have comfort issues, it’s a consideration that the bulk of the walkable land in the Solar System is not on the Earth.

The illustrating author of xkcd hit on a similar idea in Surface Area, Space without the space .

The divine names associated with Mercury all have numerological values of 8 or 64. The name of the intelligence of Mercury has a value of 260, and the name of the spirit of Mercury has a value of 2080. These values are calculated by writing out the names in Hebrew and then adding up the value of each included letter, as each Hebrew letter can represent both a sound and a numerical value.

The seal of Mercury is constructed by drawing lines that intersect every number within the magic square.

Ten Facts about Earth

Earth is the only planet in the Solar System to have water in its three states of matter: as a solid (ice), a liquid (sea, rain, etc.) and as a gas (clouds). These are all shown below. Water is, of course, the most important liquid for life.

Fact Two

Earth is almost five billion years old, although life (resembling life as we know it) has only existed on the planet for the last 150 million to 200 million years. This means that life has only been present on Earth for only 5%-10% of its lifetime.

Fact Three

Earth and Mercury are the two most dense planets in the Solar System. This means that particles inside the planet are most closely packed together.

Fact Four

The length of time it takes for Earth to orbit the Sun is 365 and a quarter days. To make up this extra quarter which isn't counted at the end of a year, we have an extra day every four years on 29th February. The next Leap Year will be in 2012.

Fact Five

Earth is gradually slowing down. Every few years, an extra second is added to make up for lost time. Millions of years ago, a day on Earth will have been 20 hours long. It is believed that, in millions of years time, a day on Earth will be 27 hours long.

Fact Six

The centre of the Earth, its core, is molten. This means that it is liquid rock which sometimes erupts onto the surface through volcanic eruptions. This core is 7,500°c, hotter than the surface of the Sun!

Fact Seven

Earth is the only planet in the Solar System not to be named after a mythical God.

Fact Eight

Despite being called Earth, only 29% of the surface is actually 'earth.' The rest of the planet's surface (71%) is made up of water.

Fact Nine

From a distance, Earth would be the brightest of the planets. This is because sunlight is reflected off the planet's water.

Fact Ten

Earth is the only planet in the Solar System known to be geologically active, with Earthquakes and volcanoes forming the landscape, replenishing carbon dioxide into the atmosphere and erasing impact craters from meteors.


  1. Arian

    to close the space?

  2. Josu?

    Improbably. It seems impossible.

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