The movement of stars across the sky has fascinated humans for thousands of years. From ancient civilizations to modern scientists, people have been trying to understand the patterns and motions of the celestial bodies above us. Stars are not stationary in the sky, but instead move in various ways depending on their location and distance from our planet. The changing positions of stars can be observed over the course of a night, a month, or even years. This movement is caused by a combination of Earth's rotation and its orbit around the sun, as well as the individual motions of the stars themselves. Understanding the movement of stars can help us track time, navigate the seas, and even discover new planets and galaxies. Through observation and study of the stars, we can gain a deeper understanding of the universe and our place within it.
Introduction to the Wonders of Astronomical Movement
Stargazing has been a human fascination for centuries. People have always been amazed by the captivating movement of stars across the sky and how they seem to dance in patterns that are so perfectly orchestrated. The movement of stars across the sky is an astronomical phenomenon that inspires awe in everyone who has ever gazed up at night.
The Beauty of Star Movement
The beauty of star movement lies in its simplicity and complexity all at once. While it may seem like a random dance in the sky, there is a science behind it that is both fascinating and intriguing. As we gaze up at night, we can observe how some stars move faster than others, while some remain stationary or move very slowly.
Understanding Star Movement
To truly appreciate the wonder of star movement, it's important to understand what causes it. The Earth rotates on its axis every 24 hours causing us to see different parts of the sky as we spin around. This rotation creates an illusion where it appears as if everything else in space is moving around us when really we are moving.
Historical Significance
The study and observation of star movements have had significant historical significance too; ancient civilizations used these observations for navigation purposes; sailors would use them to find their way on long voyages before modern-day technology was available.
Today, astronomers use advanced technology such as telescopes and computer programs to track star movements more accurately than ever before possible.
Understanding the Science Behind the Stars' Movement
The movement of stars across the sky is a beautiful and captivating sight that has fascinated humans for centuries. However, to truly appreciate this phenomenon, we must understand the science behind it.
The Earth's Rotation and Revolution
One of the key factors in star movement is our planet's rotation on its axis. As we spin on our axis, different parts of the sky become visible to us at different times. This creates an illusion that makes it appear as though stars are moving across the sky.
Additionally, Earth's revolution around the sun also plays a crucial role in star movements. As we orbit around our star, certain constellations become visible at specific times of year while others disappear from view.
Apparent vs Actual Motion
While it may appear as if stars are moving across the sky, their actual motion is much more complex than this illusion suggests. In reality, stars move through space at varying speeds and trajectories.
However, due to their immense distance from us and lack of reference points in space, these movements can be difficult to observe directly without advanced technology such as telescopes or satellites.
Proper Motion
Proper motion refers to a star's actual motion through space relative to other celestial bodies. This type of motion can be observed by tracking a star's position over time using telescopes or other instruments.
Proper motion can also provide valuable information about a star's age and characteristics; younger stars tend to exhibit greater proper motions than older ones due to differences in their formation processes.
Stellar Parallax
Stellar parallax refers to another method used for measuring stellar distances by observing apparent shifts in positions over time when comparing two observations made from different locations on Earth’s orbit around Sun (or vice versa).
This technique relies on precise measurements taken with telescopes or other instruments; however it provides astronomers with valuable information about how far away these celestial bodies really are which can help us understand more about the universe and how it works.
The Influence of Gravity
Gravity is another factor that plays a significant role in star movements. The gravitational pull of other stars and celestial bodies can affect a star's trajectory through space, causing it to move in unexpected ways or even be pulled into orbit around another object.
Additionally, the gravity of our own planet can affect the apparent motion of stars as they rise and set on the horizon.
The Fascinating Myths and Legends of the Stars' Dance
The movement of stars across the sky has been a source of inspiration for myths and legends across cultures throughout history. These stories often depict the stars as celestial beings with their own personalities and motivations, dancing across the sky in patterns that tell tales of love, war, or creation.
Greek Mythology
Greek mythology is full of stories about gods and goddesses who reside in the heavens above. One such myth tells the story of Orion, a great hunter who was placed among the stars by Zeus after his death. According to legend, Orion's constellation can be seen chasing after Taurus (the bull) across our night sky.
Another popular Greek myth involving star movement is that of Perseus and Andromeda. In this tale, Perseus rescues Andromeda from a sea monster before they are both immortalized as constellations in the night sky.
Native American Lore
Native American cultures also have their own interpretations of star movements. For example, many tribes believed that certain constellations were representations of animals or creatures important to their culture.
One such example is found among Navajo people who believe that certain constellations represent animals important to their culture like Big Dipper represents bear while Pleiades represents antelope or deer.
Chinese Astrology
Chinese astrology also plays an important role in interpreting star movements; it consists not only observing but study them carefully about how they might influence human destinies too over time.
In Chinese folklore astronomy there are many famous tales like Tanabata festival where two lovers were separated by Milky way galaxy but allowed to meet once every year on this day when Vega (a star) & Altair (another star) align together creating a bridge between them for one day only!
Best Places to Watch and Capture the Spectacular Display
The movement of stars across the sky is a captivating sight that can be enjoyed from almost anywhere in the world. However, some places offer better views than others due to their lack of light pollution or unique geographic features that enhance the viewing experience.
Dark Sky Parks
Dark sky parks are areas protected from light pollution where stargazers can enjoy unobstructed views of the night sky. These parks often have designated observation areas and host events such as astronomy lectures or guided tours.
Some famous dark sky parks around the world include:
- Natural Bridges National Monument (USA)
- Galloway Forest Park (Scotland)
- Aoraki Mackenzie International Dark Sky Reserve (New Zealand)
High Altitude Locations
High altitude locations offer excellent views of star movements because they are above much of Earth's atmosphere which causes distortion and interference with starlight. Additionally, many mountainous regions offer clear skies and low humidity which make for ideal stargazing conditions.
Some popular high altitude locations for stargazing include:
- Mauna Kea Observatory (Hawaii)
- La Palma Observatory (Spain)
- Atacama Desert (Chile)
Coastal Areas
Coastal areas also provide unique opportunities for observing star movements across our night sky. The combination of open horizons, reflective water surfaces, and generally low levels of light pollution make these regions ideal for stargazing adventures.
Some popular coastal locations for watching stars include:
- The Maldives
- Great Barrier Reef Marine Park
- Stargazing beaches in California
Tips for Capturing Great Photos
Capturing photos or videos of star movements can be challenging due to their faintness; but it's possible with some preparation & right equipment! Here are few tips to help you capture great photos-
Use a Tripod
A tripod helps keep your camera steady during long exposure shots, minimizing blur and ensuring sharp images. It is an essential tool for capturing star movement photography.
Use a Wide-Angle Lens
A wide-angle lens can capture more of the night sky in a single shot, giving you a better chance to capture star movements across the sky.
Choose the Right Time
The best time to photograph star movements is during moonless nights when there's minimal light pollution. When there is no moonlight, you can see stars much more clearly.
Experiment with Exposure Settings
Experimenting with exposure settings such as ISO, aperture and shutter speed can help you find the sweet spot for capturing stunning photos of star movement. Lower shutter speeds are commonly used for longer exposures that allow maximum light into camera sensors while aperture settings control depth-of-field (focus).
Behold the Marvels of Cosmic Ballet
The movement of stars across the sky is often described as a cosmic ballet - a captivating dance performed by celestial bodies that inspires awe and wonder in all who witness it.
The Beauty of Star Clusters
Star clusters are groups of stars that move together within the same region of space. Watching these clusters move across our night sky can be a beautiful sight, with each star seeming to complement and enhance one another's movements.
Some famous star clusters include:
- Pleiades (also known as Seven Sisters)
- Hyades
- M13 (a globular cluster)
Planetary Orbits
Planets also contribute to the cosmic ballet, moving in their own orbits around our sun. These movements can be observed from Earth with telescopes or other instruments, allowing us to track their paths across our night sky.
Some popular planets for observing include:
- Jupiter
- Saturn
- Venus
Comets and Asteroids
Comets and asteroids are small celestial objects that can also add to the beauty of star movements. As they pass through our solar system, they leave trails behind them that can be seen from Earth as bright streaks in the night sky.
Famous comets include:
- Halley's Comet
- Hale-Bopp Comet
Meteor Showers
Meteor showers occur when Earth passes through fields of debris left behind by comets or asteroids. When these debris enter Earth’s atmosphere at high speeds they create bright streaks called meteors or shooting stars which light up our skies!
Some popular meteor showers include:
- Perseids (August)
- Geminids (December)
- Leonids (November)
The Mechanics Behind Stars' Dazzling Dance
The movement of stars across the sky is a beautiful and captivating sight that has fascinated humans for centuries. But what causes this dazzling dance? In this section, we will explore the mechanics behind star movements.
Gravity and Inertia
Gravity is one of the main forces that governs star movement. Every object in our universe exerts a gravitational pull on every other object, causing them to move towards each other.
Inertia is another factor that affects star movement; it refers to an object's resistance to changes in motion. As stars move through space, their inertia allows them to continue moving in a straight line until something else interferes with their path - like gravity from another celestial body or friction from interstellar gas or dust.
Rotation and Revolution
Rotation and revolution are also key factors in star movements. Rotation refers to an object spinning around its own axis while revolution refers to an object's orbit around another celestial body such as our sun.
As Earth rotates on its axis, different parts of the sky become visible at different times which creates an illusion that makes it appear as though stars are moving across our night sky!
Similarly, as planets revolve around our sun they create unique patterns of movement which can be seen from Earth with telescopes or other instruments.
Proper motion can provide valuable information about a star's age and characteristics; younger stars tend to exhibit greater proper motions than older ones due differences in their formation processes.
Binary Star Systems
Binary star systems are pairs of stars that orbit each other around a common center of mass. These systems can provide unique insights into star movements as they allow astronomers to study the interactions between two stars as they move through space together.
Some famous binary star systems include:
- Alpha Centauri
- Sirius
- Procyon
Legends and Lore: The Culture of Celestial Movement
The movement of stars across the sky has captivated humans for thousands of years, inspiring countless legends and lore across cultures. In this section, we will explore some of the most famous stories related to celestial movements.
African Traditions
African traditions also have fascinating interpretations for celestial movements; ancient Africans had complex spiritual beliefs that linked cosmic motion with various aspects life including agriculture cycles & animal migrations etc..
For example, the Dogon tribe of Mali have a detailed knowledge of the Sirius star system which they believe is home to their ancestors. They also have knowledge about the elliptical orbit of another star that orbits Sirius!
Mayan Civilization
The ancient Maya civilization in Central America was well-known for their astronomical observations and interpretations. They believed that celestial movements were linked to human destiny and used these observations to create their famous calendar.
One such example is the Venus calendar, which tracked the planet's movements across our night sky over an eight-year cycle. According to legend, this cycle corresponded with different phases of life and influenced human destiny accordingly.
Epic Star Shows: Top Spots to Witness the Enchanting Display
The movement of stars across the sky is a breathtaking spectacle that can be enjoyed from almost anywhere on Earth. However, certain locations offer particularly stunning views of this cosmic dance. In this section, we will explore some of the best spots for witnessing epic star shows.
Dark Sky Preserves
Dark Sky Preserves are areas that have been designated as places where light pollution is minimal or nonexistent; they provide ideal conditions for stargazing and observing celestial movements.
Some famous dark sky preserves include:
- Cherry Springs State Park (Pennsylvania, USA)
- Jasper National Park (Alberta, Canada)
- Brecon Beacons National Park (Wales)
High Altitude Observatories
Observatories located at high altitudes can offer unparalleled views of the night sky due to their proximity to space and lack of atmospheric distortion.
Some famous high altitude observatories include:
- Cerro Tololo Inter-American Observatory (Chile)
Desert Regions
Desert regions are known for their clear skies and minimal light pollution which make them great spots for stargazing. These arid landscapes provide wide-open spaces with uninterrupted views of the night sky.
Some popular desert regions for stargazing include:
- Sahara Desert (North Africa)
- Mojave Desert (California, USA)
Coastal areas can also offer unique viewing opportunities as they often provide wide-open vistas with unobstructed views over large bodies of water. This creates a stunning backdrop against which celestial movements can be observed.
Some popular coastal areas for star gazing include:
- Acadia National Park in Maine
- Isle Of Skye in Scotland
- Exmouth Gulf in Australia
Awe-Inspiring Realms of Heavenly Motion
The movement of stars across the sky is a beautiful and awe-inspiring sight that has fascinated humans for centuries. In this section, we will explore some of the most incredible realms of heavenly motion.
Nebulae
Nebulae are great clouds of gas and dust that drift through space; they can be seen from Earth as glowing patches in our night sky. These cosmic formations provide an enchanting backdrop for star movements.
Some famous nebulae include:
- Orion Nebula
- Eagle Nebula
- Carina Nebula
Galaxies
Galaxies are massive collections of stars, planets, gas and dust that move together through space. The Milky Way is our galaxy, but there are countless others spread throughout the universe.
Observing these galaxies move across our night sky can be a humbling experience; it reminds us just how small we are in comparison to the vast expanse of space.
Supernovae
Supernovae are incredibly powerful explosions caused by dying stars; they can produce more energy in seconds than our sun will produce over its entire lifetime!
While supernovae themselves cannot be seen with the naked eye from Earth due to their distance away from us (typically several thousand light-years), their aftermath may create incredibly bright remnant objects like neutron stars or black holes which can give off radiation visible thousands or even millions years later!
Planetary Transits
Planetary transits occur when a planet passes directly between Earth and another celestial body such as Sun or Moon thereby blocking out some portion(s) its light creating interesting patterns on surfaces affected by it i.e., eclipses! This phenomena happens only occasionally & requires precise alignments making them extremely rare events that should not be missed if possible!
Some famous examples include:
- Transit Of Venus (2012)
- Transit Of Mercury (2016)
Auroras
Auroras (also known as Northern/Southern Lights) are beautiful light shows that occur when charged particles from the sun interact with Earth's magnetic field; they create stunning displays of color and movement in our night sky.
Auroras can be seen from locations at high latitudes near the poles, making them a unique and incredible experience for those lucky enough to witness them!
The Phenomena Explained: Science of the Stars' Movement
The movement of stars across the sky has fascinated humans for centuries, but what causes this phenomenon? In this section, we will explore the science behind the captivating movement of stars.
Earth's Rotation
The primary cause of star movement in our night sky is Earth's rotation. Our planet rotates on its axis once every 24 hours, causing celestial bodies to appear as if they are moving across our night sky.
As Earth rotates from west to east, objects in the sky appear to move from east to west. This is why stars in the northern hemisphere appear to rotate around Polaris (the North Star) and why southern hemisphere stargazers use different reference points such as Sigma Octantis!
Precession
Precession is another factor that contributes to star motion over long periods of time; it occurs when Earth's rotational axis changes orientation due to gravitational forces exerted by other celestial bodies like Sun & Moon etc.
This means that over time, different stars will become pole stars as a result of precession; for example, Vega was once a pole star and will be again in about 14 thousand years!
Mythical Interpretations of the Celestial Choreography
Throughout history, humans have looked to the stars for inspiration and guidance. As a result, many cultures have developed their own mythical interpretations of the celestial choreography. In this section, we will explore some of these fascinating myths.
Zodiac Signs
The Zodiac is a band of constellations that circle our sky; it has been used for centuries as a way to predict personality traits and future events based on when someone was born.
There are twelve signs in the Zodiac:
- Aries
- Taurus
- Gemini
- Cancer
- Leo
- Virgo
- Libra
- Scorpio
- Sagittarius
- Capricorn
- Aquarius
- Pisces
Each sign represents different characteristics based on which constellation it is associated with!
Where and When to Behold the Mesmerizing Performance
If you're looking to witness the mesmerizing movement of stars across the sky, there are a few things you need to know about where and when to look. In this section, we'll explore some tips for finding the best spots for stargazing and when to catch these celestial performances.
Finding Dark Sky Sites
The first step in finding a great spot for stargazing is finding a location with minimal light pollution. Light pollution can make it difficult (if not impossible) to see many celestial objects, so it's important that your chosen location is as dark as possible.
Some great places for stargazing include:
- National Parks
- Remote rural areas
- Mountains
- Deserts
Timing Your Stargazing
Timing is also crucial when it comes to observing star movements; different phenomena occur at different times throughout year based on their positions relative Earth's orbit around Sun!
For example, here are some notable events that occur each year:
- Orionid Meteor Shower (Oct)
- Geminid Meteor Shower (Dec)
- Perseid Meteor Shower (Aug)
These events can be seen from various locations all over world but timing varies depending on geography since they depend on where you are in relation Earth’s orbit around sun!
Tools of The Trade
While our naked eyes are capable of seeing many celestial objects; telescopes & binoculars can often enhance our viewing experience considerably too - making even fainter stars visible while providing greater detail & clarity! So don't hesitate invest in one if you're serious about stargazing!
Other useful tools include:
- Star Maps
- Red flashlights (to avoid disrupting night vision)
- Apps dedicated specifically for astronomy like 'Star Walk'
Weather Conditions
Finally, weather conditions play an important role when it comes observing star movements; cloudy skies will obviously obscure visibility while extreme weather conditions like high humidity or heavy pollution can also affect viewing experience!
Therefore, it's important to check weather forecasts before heading out for stargazing adventure to make sure you have best chance of success.
Introduction to the Enchanting Realm of Stars' Movement
The movement of stars across the sky has captivated humans for thousands of years. From ancient cultures who used star patterns to navigate, to modern astronomers who study celestial movements, the beauty and complexity of these phenomena continue to inspire us.
Awe-Inspiring Beauty
One of the most enchanting aspects of star movement is its sheer beauty. Watching stars dance across our night sky can be a truly awe-inspiring experience that leaves us feeling small but connected at same time!
Whether it's watching shooting stars streaking through atmosphere or admiring constellations as they drift slowly overhead, there's something magical about witnessing this celestial choreography with our own eyes.
Scientific Significance
Beyond their visual appeal, star movements also have significant scientific value. By studying these phenomena, astronomers can learn more about how our universe works and gain insights into some of its deepest mysteries.
For example:
- Proper motion helps astronomers track individual stars over long periods
- Stellar parallax allows us measure distances between faraway objects precisely
- Precession provides clues about Earth's rotational changes over time
- Zodiac signs & other astrological concepts provide unique cultural insights into human history too!
Cultural Significance
In addition to their scientific importance, star movements have played an important role in many cultures throughout history. From Greek mythology to Chinese astrology - different societies had unique interpretations & beliefs based on what they saw happening in night sky above them.
These stories not only helped people understand world around them but also inspired art & literature; from Renaissance paintings showing scenes from classical mythology like "The Birth Of Venus" by Botticelli which depicts goddess emerging sea onto shore fully grown and beautiful while surrounded by cherubs playing music; or even Shakespeare’s play Romeo & Juliet where lovers invoke power celestial bodies when making passionate declarations love like "O Romeo! The day/night are together!" etc.
Opportunities for Stargazing
One of the best ways to experience the enchanting realm of star movement is through stargazing! With so many breathtaking events occurring at different times and places around world, there are always opportunities to witness celestial phenomena firsthand.
Some notable events include:
- Meteor showers like Perseids, Orionids, Geminids etc.
- Eclipses (lunar & solar)
- Planetary alignments
- Transits (when planets pass in front of sun)
So grab a telescope or just your naked eyes and head out into night - there's a whole universe waiting to be explored!
The Intricate Mechanics of the Cosmic Dance
The movement of stars across the sky is not just a beautiful spectacle; it's also an intricate dance governed by complex mechanics. In this section, we will explore some of the key factors that influence star movements.
Gravity
Gravity plays a crucial role in determining how celestial bodies move through space. It's what keeps planets in their orbits around stars and holds galaxies together.
As objects with mass move closer to one another, they are drawn together by gravitational force. This force becomes stronger as objects get closer and weaker as they move further apart.
Orbits
Orbits are defined paths that celestial bodies follow around other bodies due to gravitational attraction between them. The shape, size, and orientation of an orbit depends on factors such as mass and distance between two objects.
Kepler's laws describe how planets orbit around sun:
- First law: All planets move elliptically (oval-shaped) orbits with Sun at one focus
- Second law: A line joining planet & sun will sweeps out equal areas in equal times
- Third law: Square of period (time takes complete one orbit) is proportional to cube distance between planet & Sun
Rotation
Rotation refers to spinning motion of celestial body on its own axis; it determines length day or night! Earth takes approximately 24 hours rotate once - which creates our day/night cycle.
Other celestial bodies have different rotation periods based on their size/mass; for example Jupiter rotates fully once every 10 hours while Venus completes single rotation every 243 Earth days!
Myth, Legend, and News: How We Interpret Stellar Motion
The movement of stars across the sky has inspired countless myths and legends throughout human history. In this section, we'll explore how people have interpreted stellar motion over time - from ancient cultures to modern-day news.
Ancient Myths
Many ancient cultures used star patterns to navigate and keep track of time. For example:
- The Greeks saw constellations as representations of their gods & goddesses
- The Chinese developed a complex system of astrology based on the movement of celestial bodies
- The Maya used astronomical observations to create precise calendars that still fascinate us today!
These myths helped people understand world around them while also providing inspiration for art/literature; like Homer’s epic Odyssey where hero Odysseus navigates his way home using stars guidance or Shakespeare's plays which are filled with references celestial bodies!
Scientific Interpretation
In addition to mythological interpretations, scientists also study stellar motion in order to gain deeper understanding universe's mechanics! Some notable examples include:
- Proper Motion: Studying how individual stars move through space provides clues about their age/evolution
- Galaxy Rotation: Observing rotational motion galaxies helps astronomers understand distribution dark matter within each galaxy!
- Planetary Orbits: By studying orbits planets around our Sun (as well other nearby stars), we can learn more about conditions necessary for life exist elsewhere in universe!
News and Discoveries
Finally, stellar motion continues to captivate our attention through ongoing discoveries and news stories. For example:
- In 2019, the Event Horizon Telescope captured first-ever image of black hole at center of galaxy M87
- In 2020, astronomers discovered a planet orbiting around our nearest neighboring star system Proxima Centauri!
- Recently researchers found evidence that stars are born in pairs more often than previously thought
These discoveries and findings help us appreciate the beauty and complexity of universe while also challenging us to rethink what we know about it.
Discover the Best Spots to Observe and Photograph the Celestial Ballet
If you're looking to witness the mesmerizing movement of stars across the sky, there are many incredible locations around the world where you can do so. In this section, we'll explore some of the best spots for observing and photographing this celestial ballet.
Dark Sky Reserves
Dark Sky Reserves are protected areas that have been designated as ideal locations for stargazing due to their low levels of light pollution. Some notable examples include:
- Jasper National Park in Canada
- Kerry International Dark-Sky Reserve in Ireland
- Aoraki Mackenzie International Dark Sky Reserve in New Zealand
These reserves offer clear views of starry skies without interference from artificial light sources; perfect for seeing star movements!
Remote Locations
Remote wilderness areas away from city lights are also great places to observe and photograph celestial ballet! Some popular destinations include:
- Joshua Tree National Park in California, USA
- Sossusvlei Desert in Namibia
- The Atacama Desert in Chile
These remote locations provide unobstructed views of night sky - allowing you experience beauty stellar motion like never before!
Mountains
Mountains offer high elevation vantage points which not only gives stunning panoramic views landscapes but also provides clear skies with little atmospheric distortion or light pollution. For example:
- Mauna Kea Observatory located on summit Hawaii's highest mountain is one most famous astronomical sites world!
- El Teide National Park located on Tenerife Island (Spain) offers fantastic opportunities for stargazing as well!
Special Events
Finally, special events like meteor showers or eclipses provide unique opportunities to see celestial movements up close! Some notable events include:
- Perseid meteor shower which occurs annually between July & August
- Solar eclipse when Moon passes between Sun & Earth blocking out its light completely!
- Aurora borealis (Northern Lights) which occur when charged particles from Sun interact with Earth’s magnetic field
These events draw stargazers from all over world to witness their beauty and wonder!## FAQs
What causes the stars to move across the sky?
The movement of stars across the sky is caused by Earth's rotation on its axis. The Earth rotates from west to east, and this creates the illusion of the stars moving across the sky from east to west. The stars appear to move in circles around the north and south poles.
Why do the stars appear to move in different patterns depending on the time of year?
The stars appear to move in different patterns depending on the time of year because of the Earth's orbit around the sun. As the Earth moves in its orbit, different constellations become visible in the night sky. This is why the stars appear to move in different patterns throughout the year.
Can the movement of stars be predicted and if so, how?
Yes, the movement of stars can be predicted using star charts and software programs. These tools can show the position of stars at any given time and location. Astronomers use these tools to predict the movement of stars across the sky and to locate specific stars and constellations.
Why do some stars appear to move at different speeds?
Some stars appear to move at different speeds because they are closer or farther away from Earth than other stars. Stars that are closer to Earth appear to move faster across the sky, while stars that are farther away appear to move slower. Other factors, such as the star's position in relation to Earth, can also affect its apparent speed.