Articles About Astronomy (124)
Defining Seasons
When do seasons begin and end in the two hemispheres?
Twilight, dawn, & dusk
Learn more about different kinds of twilight, dawn and dusk.
Full Moon Names
Full Moons had given names in many ancient cultures. The Full Moon names we use today often reflect nature like Harvest Moon.
Full Moon – the Moonlight Phase
The 3rd primary phase of the Moon, the Full Moon is the moment its disk is illuminated by the Sun's rays.
What's a Blood Moon?
A total lunar eclipse is often called a Blood Moon because of the red glow the eclipsed Moon gets. The term is also used for four total lunar eclipses that occur in a row.
2021 Cosmic Calendar
Celestial events and highlights of 2021 and 2022 including supermoons, solar and lunar eclipses, meteor showers, solstices, and equinoxes.
What Is a Supermoon?
The Full Moon on June 14, 2022, is a Super Strawberry Moon. Supermoon, Full Moon—what's the difference?
December Solstice
The December solstice is the shortest day the Northern Hemisphere. South of the equator, it's the longest day.
When Is Winter 2021?
Winter starts at the winter solstice. When is the winter solstice this year?
The New Moon
When is the next New Moon? New Moon is when the Sun and Moon are aligned, with the Sun and Earth on opposite sides of the Moon.
What Causes Seasons on Earth?
Seasons change because Earth's rotational axis tilts away or towards the Sun during the course of a year.
September Equinox
The Sun shines directly on the Equator on the September equinox and the length of day and night is nearly equal, but not quite.
What Is a Blue Moon?
'Once in a blue moon', suggests something is very rare. But just how rare is a Blue Moon?
June Solstice
The June solstice is the longest day of the year in the Northern Hemisphere & the shortest day in the Southern Hemisphere.
What Causes Tides?
The gravitational pull of the Moon and the Sun makes the water in the oceans bulge, causing a continuous change between high and low tide.
The Golden Hour – When Sunlight Turns Magical
When the Sun is close to the horizon, its light appears warmer and softer. Why is that so? What is the definition of the golden hour? Explanation with photography tips.
Solar and Lunar Eclipses
Solar and lunar eclipses, why they occur, when the next eclipse is, and from where you can see them.
Magnetic Declination
A compass needle doesn't point to the geographical North Pole but to magnetic north. Did you know that it usually doesn't point to the magnetic North Pole either?
March Equinox
March equinox marks the beginning of spring in the Northern Hemisphere. It is the Southern Hemisphere's autumnal/fall equinox.
Civil Twilight – Civil Dawn & Dusk
Civil twilight is the brightest of the twilight phases. How is it defined and when does it start and end? What are civil dawn and civil dusk?
First Quarter Moon
The 1st Quarter Moon is a primary Moon phase when we can see exactly half of the Moon's surface lit up. Which half depends on where you are on Earth.
When Does Fall Start?
North of the equator, fall begins in September; in the Southern Hemisphere, it starts in March. Find out exact dates and how the fall season is defined.
Total Solar Eclipse
Total solar eclipses occur when the New Moon comes between the Sun and Earth and casts the darkest part of its shadow, the umbra, on Earth.
Waxing Gibbous Moon
The Waxing Gibbous Moon is an intermediate Moon phase that starts after the First Quarter Moon and lasts until the Full Moon.
Northern and Southern Lights
What causes these colorful and dramatic light displays in the sky, and when and from where can you see them?
What Is Solar Noon?
Noon is at 12 o'clock but solar noon can be at a different time. What's the difference between the two?
Nautical Twilight – Nautical Dawn & Dusk
Nautical twilight is the second twilight phase. How is it defined and when does it start and end? What are nautical dawn and nautical dusk?
What Is Lunar Perigee and Apogee?
Lunar perigee is when the Moon is closest to Earth on its orbit. The point where the Moon is farthest from Earth is known as lunar apogee.
Third Quarter Moon
The Third or Last Quarter Moon is when the opposite half of the Moon is illuminated compared to the First Quarter.
Total Lunar Eclipses
A total lunar eclipse happens when Earth's shadow blocks the direct light from the Sun reaching the Full Moon.
When Is Spring Equinox?
The Vernal (Spring) Equinox in the Northern Hemisphere is in March. In the Southern Hemisphere, it's in September.
Equation of Time
Why doesn't the year's earliest sunset occur on the winter solstice, even though it is the shortest day of the year in terms of daylight?
Astronomical Twilight – Astronomical Dawn & Dusk
Astronomical twilight is the darkest of the twilight phases. How is it defined and when does it start and end? What are astronomical dawn and astronomical dusk?
Waning Gibbous Moon
The Waning Gibbous Moon is an intermediate Moon phase that starts after the Full Moon and lasts until half of the Moon's face remains lit-up at Third Quarter Moon.
December Solstice Facts
10 things you may not know about the December Solstice, the shortest day of the year in the Northern Hemisphere.
What Is a Solar Eclipse?
Solar eclipses happen when the Moon moves between Sun and Earth, blocking the Sun's rays and casting a shadow on Earth.
Earth's Perihelion
Earth's closest approach to the Sun is two weeks after the December solstice is a coincidence and has no special significance.
Equinox: Equal Day & Night?
Equinoxes don't have exactly 12 hours of day and night all over the world, like many believe. Such days, called equilux, do occur, but depend on your location.
Lunar Eclipse: Red Moon
Find out why a totally eclipsed Moon turns a shade of red.
Astronomical Glossary - Terms & Definitions
What do astronomers really mean when they use those technical terms?
Waxing Crescent Moon
The Waxing Crescent Moon phase starts after New Moon and lasts until half of the Waxing Moon's surface is illuminated at First Quarter Moon.
Solar Eclipse Myths
The solar eclipse has inspired many mythical stories and influenced human behavior. Even today, eclipses of the Sun are considered bad omens in many cultures.
What Is a Micromoon?
A Micromoon is the name given to a Full or New Moon when the Moon is farthest from Earth.
What Is Universal Time?
Universal Time is a solar time standard used in astronomy and to define time on Earth. How is it measured? What's the difference between UT, UT0, UT1, UT2, and UTC?
How Long Is a Day on Earth?
In terms of solar time, most days are a little longer than 24 hours. Exact day length for today and yesterday.
Earth Is Tilted
When an object the size of Mars crashed into the newly formed planet Earth around 4.5 billion years ago, it knocked it over and left it tilted at an angle.
What Is a Black Moon?
A Black Moon can be the third New Moon in a season with four New Moons or the second New Moon in the same calendar month, or even no New Moon at all.
When Is Summer Solstice?
The summer solstice in the Northern Hemisphere is in June, while in the Southern Hemisphere, it's in December.
How Often Do Solar Eclipses Happen?
There are between 2 and 5 solar eclipses every year, each one visible only in a limited area.
Waning Crescent Moon
During the Waning Crescent Moon phase, the lit-up part of the Waning Moon shrinks from the Third Quarter Moon until it disappears from view at New Moon.
What Is Local Mean Time?
Use a sundial to determine the time of day and you will probably be off by a few minutes. That's where LMT comes into play. How is it measured and what is it used for?
Annular Solar Eclipse
An annular solar eclipse is when the Moon moves in front of the Sun but leaves the outer edge of the Sun visible as a ring of fire.
What Are Moonbows?
Moonbows occur when the Moon’s light is reflected and refracted off water droplets in the air.
What Is the Umbra?
The umbra is the dark center portion of a shadow. The Moon's umbra causes total solar eclipses, and the Earth's umbra is involved in total and partial lunar eclipses.
Meteors: How to See
Dates and tips on how and where to see shooting stars from meteor showers all over the world.
What Is Dusk?
Dusk generally refers to the transition from sunset to nighttime, and the term is often used as another word for evening twilight. However, science defines dusk on the basis of the angle that the Sun makes with the horizon.
Watching Lunar Eclipses
A lunar eclipse can be seen with the naked eye, unlike solar eclipses, which have special safety requirements.
Partial Solar Eclipse
A partial solar eclipse happens when the Moon only partially covers the Sun.
What Is Dawn?
Dawn generally refers to the transition from night to day as the morning twilight brightens the sky. However, there is also a formal definition that refers to specific moments during that transition.
Altitude & Azimuth: The Horizontal Coordinate System
Learn how to use altitude (elevation) and azimuth angles to locate any object in the sky, such as stars, planets, satellites, the Sun, or the Moon.
10 Sept Equinox Facts
10 things you may not know about the September Equinox.
Timekeeping by Stars
Out and about at night without a watch or a smartphone readily available? If you are in the Northern Hemisphere use the Big Dipper and the North Star to tell the time.
Why 3 Shadows?
Objects cast 3 different shadows: umbra, penumbra, and antumbra. Why are there 3 types of shadows and how do they determine the type of an eclipse?
The Moon Illusion
Some days, the Full Moon at the horizon looks larger than a normal Full Moon. Does the Moon really change size or is this an illusion?
The Lunar Month
A lunar month is the time it takes the Moon to pass through all of the Moon phases, usually measured from a New Moon the next New Moon.
What are Asteroids?
Learn more about these space rocks orbiting the Sun.
Solar Eclipses in History
Solar eclipses were historically seen as omens that bring about death and destruction. People in many ancient civilizations tried their best to understand them.
The Blue Hour
The blue hour in the morning and evening is a favorite with photographers. How is it defined? When does it start & end? Explanation with times, degrees & photography tips.
Halos, Sundogs and Light Pillars
These are atmospheric phenomena created by the reflection and refraction of light by ice crystals in the atmosphere.
What Is a Partial Lunar Eclipse?
A partial lunar eclipse happens when the Earth moves between the Sun and the Moon, but they are not precisely aligned.
What Is the Penumbra?
The penumbra is the lighter outer part of a shadow. The Moon's penumbra causes partial solar eclipses, and the Earth's penumbra is involved in penumbral lunar eclipses.
Mercury Transit
When Mercury transits the Sun, you can see it as a tiny black dot silhouetted against the Sun's disk. The last Mercury transit was on November 11, 2019.
How to measure the sky
Measure the sky and find out distances between celestial objects using your hands and fingers.
December Solstice Customs
Learn more about the customs, traditions and events surrounding the December solstice.
What Are Polar Nights?
A Polar Night is a night that lasts for at least 24 hours. It's the opposite of Midnight Sun / Polar Day.
Make a Pinhole Projector
Make a simple pinhole projector using 2 pieces of card or paper to safely watch a projection of a solar eclipse.
What Are Comets?
Comets are small celestial bodies that orbit the Sun. Primarily made of dust and ice, many have a tail (coma) and are thought to be remnants of the formation of the Solar System.
What Is the Antumbra?
The antumbra is the lighter part of a shadow that forms at a certain distance from the object casting the shadow. It is involved in annular solar eclipses and planet transits.
A Year Is Never 365 Days
The definition of a tropical year is the time it takes the Earth to complete a full orbit around the Sun. It is approximately 365.242189 days long.
Penumbral Lunar Eclipse
A penumbral lunar eclipse occurs when the outer shadow of Earth falls on the Moon's face. It is easy to miss this type of lunar eclipse.
June Solstice Facts
11 things you may not know about the June Solstice.
Hybrid Solar Eclipse
A hybrid eclipse or annular/total eclipse starts as a total solar eclipse but changes into an annular solar eclipse. Why is that so? When is the next hybrid solar eclipse?
Solar Analemma
A Solar Analemma is a graph showing the position of the Sun in the sky above a single location at the same time of the day throughout the course of a year.
Rayleigh Scattering
Why does the sky turn red during sunrise and sunset?
Eclipse Magnitude
Eclipse magnitude is a number that astronomers associate with solar or lunar eclipses. What does it mean?
Safely See a Solar Eclipse
Protect your eyes during a solar eclipse. Sunglasses don't work.
The Moon's Far Side
The notion that there is a permanently dark side of the Moon is wrong. What is true, is that there is a far side of the Moon, a side we never see from Earth
March Equinox Facts
On Sat, March 20, 2022, day and night will be of almost equal duration in most time zones in the world.
Make a Box Pinhole Projector
Instructions on how to DIY a pinhole projector using a cardboard box and household items to safely see a solar eclipse.
Make a Solar Eclipse Projector
Make a Sun projector a pair of binoculars or a telescope to safely watch solar eclipses or a planet transit.
June Solstice Traditions
In many Northern Hemisphere cultures, the June solstice is associated with holidays, feasts and celebrations.
What Is Earthshine?
Earthshine is a dull glow that occurs when the Sun’s light reflects off the Earth's surface and illuminates the unlit portion of the Moon.
Transit of Venus: June 5-6, 2012
The 2012 Venus transit was the last chance to see this phenomenon for over 100 years. Mercury transits happen more often, the next one in 2032.
Lunar Eclipse Photography
Planning to take pictures of a lunar eclipse? Follow our guide for amazing eclipse photos! We tell you what kind of equipment you need and how to use it.
What Is a Meteor Shower
Dates and tips on how and where to see "shooting stars" from meteor showers all over the world.
Zodiacal Light
Also known as false dawn, zodiacal light is a rare optical phenomena that occur around sunset and sunrise in early spring and late fall.
Solar Eclipse Photography
Take that perfect solar eclipse photo with your camera and some extra equipment, or capture it with your mobile phone.
Length of Tropical Years 1900–2100
Exact length down to the second of tropical years ranging from 1900 to 2100. It is also known as a solar year, astronomical year, or equinoctial year.
Is a Blue Moon Blue?
A Blue Moon is a type of a Full Moon. It can also be a rare Moon that looks blue due to atmospheric dust particles.
All about Comet Lovejoy
Comet Lovejoy (C/2013 R1) is one of 3 comets that will grace the skies in November, 2013.
Jupiter and Venus Closest Conjunction of 2015
From time to time, some of the planets in our solar system are in conjunction and become visible together in the sky. Venus, Jupiter, Mars, and Mercury have all been visible in the early mornings of October 2015.
All about Comet ISON
Everything you need to know about Comet ISON or C/2012 S1.
Asteroid 2004 BL86 to Fly By Earth
On Monday, January 26, 2015 asteroid 2004 BL86 flew by at only 3 times the distance of the Moon from the Earth. It will be the largest celestial body to come this close to Earth until 2027.
2013: Year of comets
2013 is going to be a good year for comet watchers, with at least 3 comets that may be visible without the aid of sophisticated equipment.
What Is a Conjunction?
A conjunction is when planets like Mars, Jupiter, or Saturn, or other bodies like stars or the Moon, meet in the sky. Why and when do conjunctions happen?
Equinoxes and Solstices
Equinoxes and solstices are a result of Earth’s tilt and its orbit around the Sun.
Sunset and Sunrise Photography
The secrets of how to use your cellphone to take impressive pictures during sunrise and sunset.
The Moon: Our Satellite
Our Moon is the 5th-largest of the more than 200 moons in the solar system.
Taking Pictures of the Moon
With the right equipment, a little time and planning, you can take great pictures of the Moon.
The Moon Phases
There are four primary Moon phases and four intermediate phases. New Moon First Quarter Full Moon Third or Last Quarter Waxing and Waning Crescent Moon.
Brightest Comet of 2018
Comet 46P/Wirtanen will grace the night sky in December 2018. Find when, how, and where to see the brightest comet of the year with your naked eyes.
Brightest Comet of 2020
Comet C/2020 F3 NEOWISE will grace the night sky in July 2020. Find when, how, and where to see the brightest comet of the year with your naked eyes.
Great Conjunction 2020
In December 2020, Jupiter and Saturn met in the sky in a rare Great Conjunction.
What Is a Planet?
A celestial body needs to pass three tests to be called a planet.
The Solar System
Everything that orbits the Sun is part of the solar system.
The Sun: Our Home Star
Energy from the Sun reaches Earth in the form of solar radiation, or sunlight.
Mars: The Red Planet
Mars is the outermost of the Solar System’s small inner planets.
Venus: Our Twin Planet
There is much that is similar—and much that is different—between Venus and Earth.
Earth: The Living Planet
Earth is the largest of the Solar System’s rocky inner planets.
Saturn: The Ringed Planet
Saturn is easily visible with the naked eye, although a small telescope is required to see its rings.
Uranus: The Sideways Planet
Uranus is the seventh planet from the Sun. It was the first “new” planet to be discovered.
Mercury: The Iron Planet
Mercury, which is made mostly of iron, is the smallest planet, and the closest to the Sun.
Jupiter: The Massive Planet
Jupiter is fifth in line from the Sun, and the largest planet in the solar system.
Neptune: The Blue Planet
Neptune is too far away to be seen with the naked eye, but a good pair of binoculars can capture its blue tint.