Why Is The Moon Bright? Your Moon Questions Answered by an Astronomer

Why Is The Moon Bright? Your Moon Questions Answered by an Astronomer

If you stepped outside on the weekend and thought, “Gosh, the full moon looks nice tonight”, you are not alone.

According to Google Trends, Moon-related searches are up by more than 60% over the past week in Australia, led by Western Australia and Queensland.

Technically, the Moon is currently “waning gibbous” which means the moment of maximum fullness has passed, and it’s now starting to look smaller. But it’s still quite spectacular.

As someone teaching first-year astronomy at the moment, where much time is spent discussing the Moon, here are my answers to some of the most common recent Moon questions.

1. A full moon is how many times brighter than a half moon?

You might think a half moon (first quarter or last quarter, depending on where you are in the phases) is half as bright as the full moon. However, if you add up all the light being reflected from the Moon to us here on Earth, a half moon is a fair bit less than half as bright as the full moon. In fact, the full moon is roughly six times brighter than the half moon.

Phases of the Moon.Phases of the Moon. Shutterstock

The main reason for this comes down to shadows. When the Moon is full, the Earth is between the Sun and the Moon. So when you look at the Moon rising in the evening, the Sun has just set, behind your back.

That means the side of the Moon facing Earth is fully illuminated. With the Sun at our backs, shadows cast by objects on the Moon are pointing away from us, hidden from view. So we see the maximum amount of the Moon lit up, nice and bright.

At half moon, however, the Sun is shining onto the Moon from one side so the craters, mountains, rocks and pebbles on the Moon all cast shadows. That reduces the amount of the Moon’s surface that’s lit up, so less light is reflected towards us than you’d otherwise expect.

Interestingly, the actual surface of the Moon isn’t that reflective. If the Moon and Venus were side by side and you zoomed in to look at the surface brightness of a patch on Venus and compared it with the surface brightness of a patch on the Moon, you’d see the patch on Venus is brighter. It’s more reflective because Venus has a lot of clouds that help reflect light back to Earth.

But because the Moon is closer to Earth, it looks bigger than Venus, so the total amount of light that is reflected back to us is bigger. When you look up at night, the Moon will seem much brighter than Venus.

There’s one extra reason the full moon is extra bright - and it’s called the opposition surge. When the Moon is full (or almost full), the surface we see appears to be a little bit brighter than at all other times.

While the fact that shadows are hidden is part of the puzzle, that isn’t enough to explain all of the brightening of the Moon in the day or so around full moon. The “opposition surge” is the final piece in the puzzle that makes the full moon so much brighter than the half moon. It’s something we see in all other rocky and icy objects in the Solar system, too.

2. Why is the Moon bright?

At the time of writing, we’re within 24 hours of full moon, so it looks big and bright in the sky. It looks so much bigger than everything else in the night sky because it’s near us, and so bright because it’s reflecting light from the Sun.

But the Moon is moving away from Earth at almost 4cm per year. In the olden days, it would have been even bigger and brighter. It would have been much closer to Earth if we’d been around when Earth was young. However, the Sun was a fair bit less luminous back then, so it’s hard to say exactly how bright the Moon would have been.

why is the moon brightIn the olden days, the Moon would have been closer to Earth than it is now. Shutterstock

3. Is Easter a full Moon?

No. Easter is the first Sunday after the first full moon after the March equinox.

The March equinox is the point in the year when the Sun crosses the Equator in the sky, passing from the southern hemisphere to the northern hemisphere.

To astronomers, this is the start of the northern hemisphere’s spring; for those of us in the southern hemisphere, it marks the start of astronomical autumn. The March equinox typically falls around March 21.

The time between two consecutive full moons is roughly 29.5 days. This means the date of Easter can move around quite a lot.

4. What is the worm Moon?

This is a US thing. According to US reports, the name might refer to earthworms appearing in the soil as the weather warms in the northern hemisphere. It’s been reported this reflects detail from Native American knowledge systems.

It’s important we recognise traditional astronomy, but it’s worth noting this naming convention comes from Native American culture rather than our own Indigenous cultures.

5. How long does a full moon last?

Technically, the exact “moment” the Moon is fullest is the moment it is exactly opposite the Sun in the sky. That happens once every 29 days or so. It is the moment the Moon is most illuminated.

So how long does that last? In reality, it is a split second - the moment of maximum fullness is fleeting.

Either way, if you saw the full moon and thought it might be a nice night to go on a date, you probably have a couple of days left when the Moon will still look impressive and amazing in the sky.

 The ConversationAbout the Author

Jonti Horner, Professor (Astrophysics), University of Southern Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.


 Get The Latest By Email

Weekly Magazine Daily Inspiration

You May Also Like


Observations From Nova Scotia To Florida And Back
Observations from Nova Scotia to Florida and Back
by Robert Jennings, Innerself.com
Nova Scotia is a Canadian province of around 1,000,000 people and our home county in Florida has…
How To Ensure That "Luck" Is On Your Side
How To Ensure That "Luck" Is On Your Side
by Marie T. Russell
"He's so lucky! She always wins! I'm just not lucky!" Do these statements sound familiar? Have they…
face of woman floating in water
How To Develop Courage and Move Out of Your Comfort Zone
by Peter Ruppert
Courage is not about being fearless in the face of a scary situation. It is the willingness to move…
chamomile plants in bloom
Horoscope Current Week: July 26 - August 1, 2021
by Pam Younghans
This weekly astrological journal is based on planetary influences, and offers perspectives and…
Having The Courage To Live Life and Ask For What You Need Or Want.
Having The Courage To Live Life and Ask For What You Need Or Want
by Amy Fish
You need to have the courage to live life. This includes learn­ing to ask for what you need or…
man passed out on a table with an empty bottle of alcohol with child looking on
Can LSD Cure the 'Spiritual Disease' of Alcoholism?
by Thomas Hatsis
Beginning in the late 1950s, five hospitals (in the province of Saskatchewan in Canada) offered a…
pregnant woman sitting with her hands on her belly
Essential Tips for the Journey: Release Fear and Take Care of Yourself
by Bailey Gaddis
Suppressing fear-induced emotions infuses life into them, often causing a manifestation of…
person radiating love and light from their heart out into the universe
Being A Light unto this World: Healing the World by Being Present
by William Yang
A bodhisattva brings healing into this world not out of fear of sickness and death, but out of…

Marie T. Russell's Daily Inspiration


hear no evil, see no evil, speak no evil image of children
Death Denial: Is No News Good News?
by Margaret Coberly, Ph.D., R.N.
Most people are so strongly habituated to death denial that when death appears they are caught…
Having The Courage To Live Life and Ask For What You Need Or Want.
Having The Courage To Live Life and Ask For What You Need Or Want
by Amy Fish
You need to have the courage to live life. This includes learn­ing to ask for what you need or…
Writing letters by hand is the best way to learn to read
Writing letters by hand is the best way to learn to read
by Jill Rosen, Johns Hopkins University
Handwriting helps people learn reading skills surprisingly faster and significantly better than…
How Living On The Coast Is Linked To Poor Health
How Living On The Coast Is Linked To Poor Health
by Jackie Cassell, Professor of Primary Care Epidemiology, Honorary Consultant in Public Health, Brighton and Sussex Medical School
The precarious economies of many traditional seaside towns have declined still further since the…
image of the planet Jupiter on the skyline of a rocky ocean shore
Is Jupiter a Planet of Hope or a Planet of Discontent?
by Steven Forrest and Jeffrey Wolf Green
In the American dream as it's currently dished up, we try to do two things: make money and lose…
spraying for mosquito 07 20
This new pesticide-free clothing prevents 100% of mosquito bites
by Laura Oleniacz, NC State
New insecticide-free, mosquito-resistant clothing is made from materials researchers have confirmed…
test your creativity
Here's how to test your creativity potential
by Frederique Mazerolle, McGill University
A simple exercise of naming unrelated words and then measuring the semantic distance between them…
two children reading a book with their father
Empathy Starts Early: 5 Australian Picture Books That Celebrate Diversity
by Ping Tian, University of Sydney and Helen Caple, UNSW
Early exposure to diverse story characters, including in ethnicity, gender and ability, helps young…

follow InnerSelf on

facebook icontwitter iconyoutube iconinstagram iconpintrest iconrss icon

 Get The Latest By Email

Weekly Magazine Daily Inspiration



New Attitudes - New Possibilities

InnerSelf.comClimateImpactNews.com | InnerPower.net
MightyNatural.com | WholisticPolitics.com | InnerSelf Market
Copyright ©1985 - 2021 InnerSelf Publications. All Rights Reserved.