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Articles About Astronomy (107)

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. more

The Moon Phases

There are 4 primary Moon phases and 4 intermediate phases. New Moon First Quarter Full Moon Third or Last Quarter Waxing and Waning Crescent Moon. more

The Full Moon

The Full Moon is the moment the entire face of the Moon is illuminated by the Sun's rays. It is the 3rd primary phase. Each Full Moon has a name, except the Blue Moon. more

2018-2019 Cosmic Calendar

Astronomical events and highlights of 2018-2019 including supermoons, solar and lunar eclipses, meteor showers, solstices, and equinoxes. more

What Is a Supermoon?

A Supermoon looks bigger than an average Full Moon, and happens when a Full or New Moon is near the Moon's closest approach to Earth, its perigee. more

December Solstice

The December solstice is the summer solstice in the Southern Hemisphere and the winter solstice in the Northern Hemisphere. more

The New Moon

In modern astronomy, the New Moon is when the Sun and Moon are aligned, with the Sun and Earth on opposite sides of the Moon. The New Moon also has important cultural and religious significance worldwide. more

What Causes Seasons?

Seasons change because Earth's rotational axis tilts away or towards the Sun during the course of a year. more

September Equinox

The Sun shines directly at the Equator on the September equinox and the length of day and night is nearly equal, but not quite. more

June Solstice

The June solstice is the longest day of the year in the Northern Hemisphere & the shortest day in the Southern Hemisphere. more

What Causes Tides?

The combined gravitational force of the Moon and the Sun causes the tides in Earth's oceans. There are 2 high tides and 2 low tides every 24 hours and 50 minutes (lunar day). more

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? more

The March Equinox

The March equinox is the spring (vernal) equinox in the Northern Hemisphere and fall (autumnal) in the south. Night and day are nearly the same length. more

First Quarter Moon

The First Quarter Moon is a primary Moon phase when we can see exactly half of the Moon's surface illuminated. If it is the left or right half, depends on where you are on Earth. more

When Is Fall Equinox?

The fall (autumnal) equinox in the Northern Hemisphere is in September. In the Southern Hemisphere, it's in March. more

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. more

Waxing Gibbous Moon

The Waxing Gibbous Moon is an intermediate Moon phase which starts after the First Quarter Moon and lasts until the Full Moon. more

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? more

What Is Lunar Perigee and Apogee?

The Moon's orbit around Earth is elliptical. The point of the orbit closest to Earth is called perigee, while the point farthest from Earth is known as apogee. more

Third Quarter Moon

The Third or Last Quarter Moon is when the opposite half of the Moon is illuminated compared to the First Quarter. more

Total Lunar Eclipses

A total lunar eclipse happens when Earth's shadow blocks the direct light from the Sun reaching the Full Moon. more

When Is Spring Equinox?

The Vernal (Spring) Equinox in the Northern Hemisphere is in March. In the Southern Hemisphere, it's in September. more

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? more

Waning Gibbous Moon

The Waning Gibbous Moon is an intermediate Moon phase which starts after Full Moon and lasts until half of the Moon's surface is illuminated at Third Quarter Moon. more

December Solstice Facts

10 things you may not know about the December Solstice, the shortest day of the year in the Northern Hemisphere. more

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. more

Earth's Orbit & Solstice

Earth's closest approach to the Sun is 2 weeks after the December solstice is a coincidence and has no special significance. more

Equinox: Equal Day & Night?

Equinoxes don't have exactly 12 hours of day and night all over the world, like many believe. Such days do happen, but depend on the latitude of your city. more

Waxing Crescent Moon

Waxing Crescent Moon is an intermediate Moon phase which starts after New Moon and lasts until half of the Moon's surface is illuminated at First Quarter Moon. more

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. more

What Is Universal Time (UT)?

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? more

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. more

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. more

Waning Crescent Moon

During the Waning Crescent Moon phase, the illuminated part of the Moon decreases from a semicircle at Third Quarter until it disappears from view entirely at New Moon. more

What Is Local Mean Time (LMT)?

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? more

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. more

What Are Moonbows?

Moonbows occur when the Moon’s light is reflected and refracted off water droplets in the air. more

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. more

Meteors: How to See

Dates and tips on how and where to see shooting stars from meteor showers all over the world. more

Dusk – Definition and Meaning

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. more

Watching Lunar Eclipses

A lunar eclipse can be seen with the naked eye, unlike solar eclipses, which have special safety requirements. more

Dawn – Definition and Meaning

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. more

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. more

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. more

Why 3 Shadows?

The Earth and the Moon cast 3 different shadows: umbra, penumbra, and antumbra. Why are there 3 types of shadows and how are they defined? more

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? more

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. more

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. more

Blue Hour – Magic 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. more

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. more

Mercury Transit

Local time for Mercury transit November 11/12, 2019. Visible from most of the world. Will you be able to see it? Map of path and animation. more

Midnight Sun

Midnight Sun, or polar day, means that at least a sliver of the Sun's disk is visible above the horizon 24 hours of the day. more

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. more

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. more

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. more

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. more

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. more

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. more

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? more

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. more

Eclipse Magnitude

Eclipse magnitude is a number that astronomers associate with solar or lunar eclipses. What does it mean? more

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 more

March Equinox Facts

On Wednesday, March 20, 2019, the day and night are of almost equal duration in most time zones in the world. more

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. more

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 May 2016. more

Lunar Eclipse Photography

It takes both skill and good equipment to photograph a lunar eclipse aka a Blood Moon. Here are a few tips to help you on your way. more

Zodiacal lights

Also known as false dawn, zodiacal lights are rare optical phenomena that occur around sunset and sunrise in early spring and late fall. more

Solar Eclipse Photography

It takes some skill and some extra equipment to take dramatic pictures of a solar eclipse. But it is possible to capture the mood even with a simple cell phone camera. more

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. more

Venus - Jupiter - Mars Conjunction

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. more

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. more

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. more

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. more

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