Solar Radiation & Temperature
Monday, June 22, 2026 7:59 AM
The temperature of an object or substance is measured by its thermal energy. If an object
increases in temp, it’s because it’s absorbing more energy than losing it
- The earth’s air temp is a measure of the amount of energy air molecules have absorbed
- The sun supplies the earth with 99.97% of its heat
The remainder is supplied by the earth’s interior, in the form of geothermal heat, creating
earthquakes, geysers, & volcanic eruptions
- Geothermal heat is not significant in providing atmospheric heat, but it’s crucial in its effects
on earth’s landforms:
○ The sun is a star & is one of over 2 hundred billion in the Milky Way Galaxy
- Without the sun, there would be no life on earth because its the nearest star to the earth &
is the original source of most energy used on this planet
○ Without the sun, we would be extremely cold & have no weather variations, heat from
the sun stirs the atmosphere into motion, creating wind, clouds, rain & snow.
○ The sun is over 100x larger than earth & is located some 93 million miles away from
the earth. The surface temperature of the sun is estimated to be about 10,000
degrees F.The sun emits energy traveling to earth at the speed of light (186,000
mi/sec) as radiation.
- Because of our distance from the sun, earth receives a fraction of the sun's total radiation,
about 1/2,000,000,000,000 (1/2billionths)
Radiation
- Have you ever noticed how warm your face feels in front of a campfire on a cold evening?
Energy from the fire is being transferred through the air to your face, which absorbs this
energy & converts it into heat. The energy that’s transferred is called radiant energy aka
radiation
○ It travels in waves that release energy when absorbed by an object. Because these
waves have electric & magnetic properties, we call them "electromagnetic waves"
Wave Characteristics
- Electromagnetic radiation is energy traveling in waves of many lengths & in all directions
from the sun. Low points (valleys) of the waves are called troughs, high points (ridges)
are the crests & the horizontal distance between the crest of one wave & the next is the
wavelength usually expressed by a Greek letter λ lambda
- We measure everyday things using meters, cm, or inches, when measuring the
wavelengths of radiation in terms of micrometers (µm), it is equal to one-millionth of a
meter. 1 micrometer µm = one-millionth of a meter
○ So how big is a wavelength? Imagine the diameter of a piece of human hair split into
100 parts, is about the distance of 1 micrometer
Radiation & Temperature
- All objects & substances on earth emit radiation; your body, desks, your notes, the air,
trees, a cold glass of soda, are all radiating a wide range of electromagnetic waves. The
wavelengths each object/substance emit depends on the object's temp. The higher the
temp, the faster the object's particles are vibrating & shorter wavelengths of radiation
emitted
- This can be visualized by attaching a long rope to a post & holding the other end. If you
shake the rope rapidly (similar to a high temps & particles vibrating rapidly), many short
waves travel along the rope. If you shake it slowly (A lower temp & particles vibrating
slowly) few long waves travel along the rope
- Basic Principles of Radiation
○ The hotter the object, the shorter the wavelength of radiation & the greater the
intensity. For example, the sun has an average temp of 10,000 degrees F that
radiates a lot more energy than the earth w/ an average temp of about 59 degrees
F. The sun emits shorter wavelengths than the earth does.
○ Solar radiation is mostly shortwaves (less than 2µm), while the earth emits most
radiation at longer wavelengths (4-25µm). For this reason, the earth’s radiation is
called longwave radiation, where the sun’s energy is shortwave radiation. The earth
is a huge radiation converter; it absorbs the sun’s shortwave radiation & emits
longwave radiation back to space.
Electromagnetic Spectrum
- All radiation is divided into several major categories on the basis of wavelength to form
an electromagnetic spectrum. They are arranged from longer (less energetic)
wavelengths to shorter (more energetic) wavelengths
- Waves with a length of between 0.4 & 0.7 micrometers can be detected by the human
eye. Aka visible light, about 44% of the radiation that the sun emits falls within this
zone. As you look around your room, everything you see has these waves bouncing off of
them. If they didn’t, you would not be able to see them. What your eyes pickup & turn
into a picture in your brain are these visible light waves
- About 7% of the sun’s energy that reaches the earth is ultraviolet radiation, which can
burn your skin. Most of these waves are blocked by ozone in the Earth’s upper
atmosphere
- About 48% of the sun’s emitted rays that reach earth are infrared waves, felt as
heat. While only some of the sun’s energy falls in the infrared portion of the spectrum,
the relatively cooler earth emits most of its energy at infrared wavelengths.
Solar Constant
Although the amount of shortwave energy that earth receives from the sun varies, it can still
be considered constant. The amount of solar radiation received at the outer part of the
atmosphere is called the solar constant.
So what is the value of the solar constant? The solar constant is the constant amount of
incoming solar radiation at the of the earth's atmosphere. It has been measured (by
satellites) at 1,327 watts/square yard. You can imagine the intensity of that heat when your
average light bulb is 60-100 watts. Have you ever touch a hot light bulb? That is only a
fraction of the intensity of heat put out by the sun at the top of the atmosphere.
The amount of energy received at the top of the atmosphere, although considered a constant,
varies on earth. It is not uniform from place to place because, as we have learned, there are
places that receive more daylight than others throughout the year. The value of the solar
constant varies more at the poles than the tropics. You may recall, there are times that the
poles receive 24 hours daylight (radiation), and thus they are receiving double the energy than
the equator with around 12 hours of daylight. But then again, there are times that the poles
receive 0 daylight and thus 0 radiation, too. Averaged over a full year, locations at the
equator receive almost 2 1/2 times more energy than areas near the North Pole or South Pole.
Solar Insolation
Once solar radiation travels through the atmosphere, it is referred to as "solar
insolation." INSOLATION is short for "incoming solar radiation." The amount of insolation
received at the surface of the earth is about 1/2 of the amount received at the top of the
atmosphere. That means about 50% of the solar radiation is "lost" as it travels through the
atmosphere! There are variations in the amount depending on latitude. Generally, higher
latitudes receive less insolation than lower latitudes.
Monday, June 22, 2026 7:59 AM
The temperature of an object or substance is measured by its thermal energy. If an object
increases in temp, it’s because it’s absorbing more energy than losing it
- The earth’s air temp is a measure of the amount of energy air molecules have absorbed
- The sun supplies the earth with 99.97% of its heat
The remainder is supplied by the earth’s interior, in the form of geothermal heat, creating
earthquakes, geysers, & volcanic eruptions
- Geothermal heat is not significant in providing atmospheric heat, but it’s crucial in its effects
on earth’s landforms:
○ The sun is a star & is one of over 2 hundred billion in the Milky Way Galaxy
- Without the sun, there would be no life on earth because its the nearest star to the earth &
is the original source of most energy used on this planet
○ Without the sun, we would be extremely cold & have no weather variations, heat from
the sun stirs the atmosphere into motion, creating wind, clouds, rain & snow.
○ The sun is over 100x larger than earth & is located some 93 million miles away from
the earth. The surface temperature of the sun is estimated to be about 10,000
degrees F.The sun emits energy traveling to earth at the speed of light (186,000
mi/sec) as radiation.
- Because of our distance from the sun, earth receives a fraction of the sun's total radiation,
about 1/2,000,000,000,000 (1/2billionths)
Radiation
- Have you ever noticed how warm your face feels in front of a campfire on a cold evening?
Energy from the fire is being transferred through the air to your face, which absorbs this
energy & converts it into heat. The energy that’s transferred is called radiant energy aka
radiation
○ It travels in waves that release energy when absorbed by an object. Because these
waves have electric & magnetic properties, we call them "electromagnetic waves"
Wave Characteristics
- Electromagnetic radiation is energy traveling in waves of many lengths & in all directions
from the sun. Low points (valleys) of the waves are called troughs, high points (ridges)
are the crests & the horizontal distance between the crest of one wave & the next is the
wavelength usually expressed by a Greek letter λ lambda
- We measure everyday things using meters, cm, or inches, when measuring the
wavelengths of radiation in terms of micrometers (µm), it is equal to one-millionth of a
meter. 1 micrometer µm = one-millionth of a meter
○ So how big is a wavelength? Imagine the diameter of a piece of human hair split into
100 parts, is about the distance of 1 micrometer
Radiation & Temperature
- All objects & substances on earth emit radiation; your body, desks, your notes, the air,
trees, a cold glass of soda, are all radiating a wide range of electromagnetic waves. The
wavelengths each object/substance emit depends on the object's temp. The higher the
temp, the faster the object's particles are vibrating & shorter wavelengths of radiation
emitted
- This can be visualized by attaching a long rope to a post & holding the other end. If you
shake the rope rapidly (similar to a high temps & particles vibrating rapidly), many short
waves travel along the rope. If you shake it slowly (A lower temp & particles vibrating
slowly) few long waves travel along the rope
- Basic Principles of Radiation
○ The hotter the object, the shorter the wavelength of radiation & the greater the
intensity. For example, the sun has an average temp of 10,000 degrees F that
radiates a lot more energy than the earth w/ an average temp of about 59 degrees
F. The sun emits shorter wavelengths than the earth does.
○ Solar radiation is mostly shortwaves (less than 2µm), while the earth emits most
radiation at longer wavelengths (4-25µm). For this reason, the earth’s radiation is
called longwave radiation, where the sun’s energy is shortwave radiation. The earth
is a huge radiation converter; it absorbs the sun’s shortwave radiation & emits
longwave radiation back to space.
Electromagnetic Spectrum
- All radiation is divided into several major categories on the basis of wavelength to form
an electromagnetic spectrum. They are arranged from longer (less energetic)
wavelengths to shorter (more energetic) wavelengths
- Waves with a length of between 0.4 & 0.7 micrometers can be detected by the human
eye. Aka visible light, about 44% of the radiation that the sun emits falls within this
zone. As you look around your room, everything you see has these waves bouncing off of
them. If they didn’t, you would not be able to see them. What your eyes pickup & turn
into a picture in your brain are these visible light waves
- About 7% of the sun’s energy that reaches the earth is ultraviolet radiation, which can
burn your skin. Most of these waves are blocked by ozone in the Earth’s upper
atmosphere
- About 48% of the sun’s emitted rays that reach earth are infrared waves, felt as
heat. While only some of the sun’s energy falls in the infrared portion of the spectrum,
the relatively cooler earth emits most of its energy at infrared wavelengths.
Solar Constant
Although the amount of shortwave energy that earth receives from the sun varies, it can still
be considered constant. The amount of solar radiation received at the outer part of the
atmosphere is called the solar constant.
So what is the value of the solar constant? The solar constant is the constant amount of
incoming solar radiation at the of the earth's atmosphere. It has been measured (by
satellites) at 1,327 watts/square yard. You can imagine the intensity of that heat when your
average light bulb is 60-100 watts. Have you ever touch a hot light bulb? That is only a
fraction of the intensity of heat put out by the sun at the top of the atmosphere.
The amount of energy received at the top of the atmosphere, although considered a constant,
varies on earth. It is not uniform from place to place because, as we have learned, there are
places that receive more daylight than others throughout the year. The value of the solar
constant varies more at the poles than the tropics. You may recall, there are times that the
poles receive 24 hours daylight (radiation), and thus they are receiving double the energy than
the equator with around 12 hours of daylight. But then again, there are times that the poles
receive 0 daylight and thus 0 radiation, too. Averaged over a full year, locations at the
equator receive almost 2 1/2 times more energy than areas near the North Pole or South Pole.
Solar Insolation
Once solar radiation travels through the atmosphere, it is referred to as "solar
insolation." INSOLATION is short for "incoming solar radiation." The amount of insolation
received at the surface of the earth is about 1/2 of the amount received at the top of the
atmosphere. That means about 50% of the solar radiation is "lost" as it travels through the
atmosphere! There are variations in the amount depending on latitude. Generally, higher
latitudes receive less insolation than lower latitudes.
