The night sky is filled with light from all directions, like stars burning brightly in the dark. Other celestial bodies, such as planets, reflect light from the Sun, which makes them "shine" in the middle of the night sky. If when you see an object in the sky you cannot distinguish whether it is a star or a planet, you should learn to identify the physical characteristics of each of these celestial bodies. Also, one way to more easily differentiate between the two is to maximize your visibility of the night sky.
Part 1 of 3: Observe the Physical Differences
Step 1. Check if the object in question is blinking
One of the easiest ways to distinguish between a star and a planet in the middle of the night sky is by determining whether the object you are observing is blinking or shining. You can usually find out with the naked eye, as long as you have a clear view of the sky and pay attention for a long time.
- The stars twinkle and shine (hence the song “Shine Little Star”).
- The planets do not blink. On the contrary, their brightness is constant and they never disappear in the middle of the night sky.
- If you look at the sky with a telescope, the planets may appear "in motion" at the edges.
- If an object blinks or glows, it is probably a star. However, it can also be an airplane moving rapidly through the night sky.
Step 2. See if the object comes out and goes on
Celestial objects are not fixed in the sky, but move. However, their type of displacement can be a good indicator of whether they are stars or planets.
- The planets rise in the east and set in the west. In the terrestrial sky, they tend to follow a celestial trajectory similar to the Sun and the Moon.
- The stars move, but they do not rise or set, but instead orbit in a circular pattern around Polaris (Pole Star).
- If the celestial object you see appears to be moving in an apparently straight line across the night sky, it is most likely a planet.
- Satellites also move across the night sky, but faster than planets. While a planet can take hours or even weeks to move across the sky, a satellite can move in a matter of minutes.
Step 3. Recognize the ecliptic
Planets are always located along an imaginary belt throughout the night sky known as the ecliptic. This belt is not actually a visible object, but if you look closely, you will be able to find the location where the celestial bodies meet. While stars can also appear on this invisible belt, they can be distinguished thanks to their shiny appearance.
- Of the celestial bodies along the ecliptic, Mercury, Venus, Mars, Jupiter, and Saturn are considerably brighter than the surrounding stars. This is because they are close to the Sun, as they reflect the light that it emits.
- The easiest method of finding the ecliptic is by noting the location and trajectory of the Sun and Moon in relation to your location on Earth. The path of the Sun across our sky is very similar to that of the planets through the ecliptic.
Step 4. Pay attention to color
Keep in mind that not all planets have some color, but many of the larger ones appear to have some type of coloration when we see them in the night sky. This can help you differentiate them from the stars. While some with exceptionally good eyesight can detect subtle coloration, this is generally in the range of bluish-white to yellowish-white. Most people see white stars with the naked eye.
- Mercury is usually gray or medium brownish in color.
- Venus appears pale yellow in color.
- Mars is generally pale pink to bright red in color. This depends on the relative brightness or darkness of the planet, which changes every two years.
- Jupiter has an orange appearance with bands of white.
- Saturn generally has a pale gold color.
- Uranus and Neptune are pale blue in color, but are not usually visible to the naked eye.
Step 5. Compare the relative brightness of the stars and planets
While they both light up in the night sky, the planets tend to be brighter than many of the stars. Astronomers analyze the relative brightness of celestial objects using an astronomical magnitude scale, which includes most planets within the range of objects easily visible to the naked eye.
- Planets reflect light from our sun, which is relatively close to Earth. On the contrary, the stars emit their own light.
- Some stars may be much larger and brighter than our sun, but they are at a much greater distance from Earth than the planets in our solar system. Because of this, planets (which reflect sunlight) normally look brighter when viewed from Earth.
Part 2 of 3: Observing the Celestial Bodies
Step 1. Bring star maps and planetary guides
Regardless of whether you don't have good eyesight at night or simply don't know the location of certain celestial bodies for sure, a map or guide can help you determine where to look. You can buy the star maps or planetary guides in a bookstore, print them on the Internet or download an application on your smartphone.
- Remember that star maps are usually only useful for a limited time (usually about a month). This is because the location of the stars in the sky changes as the Earth continues to move around its orbit.
- If you are going to consult a star map or planetary guide while you are outside, be sure to use a dim red flashlight. These devices are designed to emit light without affecting your eyes' ability to adapt to darkness.
Step 2. Get a quality telescope or binoculars
If you can't see many celestial bodies when looking at the stars with the naked eye, consider using a telescope or binoculars. With them, you can amplify the area you are observing. In addition, they can make visible objects sharper and can even allow you to see those that you cannot see with the naked eye.
- Some experts recommend that you get used to observing celestial objects with the naked eye, then using binoculars, and finally using a telescope. In this way, you will be more familiar with visible bodies and their location in the night sky.
- Search the internet for various models of telescopes and binoculars before purchasing one. Once you find a model that interests you, read the comments of the people who have owned it.
Step 3. Go to a place with a dark sky
Light pollution from urban areas can radically limit your ability to observe celestial bodies in the night sky. If you want to have as much visibility as possible, consider going to a place with a dark sky. The International Dark Sky Association (IDA) has identified these designated places as worthy of protection from light pollution and urban development.
- The most popular places where you can see the dark sky are state and national parks, although there are others that are surrounded by well-lit and developed regions.
- Check the IDA website to find a place with a dark sky near where you live.
Part 3 of 3: Identify Factors Limiting Visibility
Step 1. Check if there are any hidden prognoses
An occultation is the process in which the Moon passes between the Earth and a certain star or planet, thus obstructing the visibility of said celestial body. These obstructions occur regularly and it is possible to plan your observation thanks to the fact that it is possible to predict them.
- Occultations can be seen from some places on Earth and not from others. Check in advance if an occultation is predicted and if your visibility of the sky will be significantly affected.
- To find out if there are predicted occultations, you can search the Internet or consult an astronomical guide. The International Occultation Timing Association publishes its forecasts on the Internet free of charge.
Step 2. Identify the moon phase
The light reflected from the moon can reduce your visibility of the stars and planets, so if the full moon is near, you will probably have difficulty observing the celestial bodies. Therefore, it is best to find out the current moon phase before venturing outside to view the night sky.
If you are unsure about the current moon phase, you can consult a free online guide that includes the phases of the moon. The United States Navy website will allow you to check the moon phases by date up to the year 2100
Step 3. Find the appropriate conditions
If the night sky is not very clear, it will not be of much use to know how to distinguish between stars and planets alone. Your ability to observe celestial bodies can be limited by a number of factors, both artificial and natural.
- Light pollution is one of the biggest limiting factors in the visibility of the night sky. Therefore, if you live near a metropolitan area, you may need to travel to a more rural area to increase your visibility.
- Clouds and large amounts of snow can affect your visibility of the night sky. If the sky is very cloudy or if the land is heavily covered in snow, you will probably have trouble seeing celestial bodies.
Step 4. Avoid other limiting factors
There are many additional factors that can affect your visibility of the night sky, some of which may be caused by you. For example, your level of alcohol, nicotine and dilated pupils when observing the sky can affect your ability to appreciate celestial bodies. These factors affect your visual ability, preventing your eyes from adapting to the dark, and identifying the stars and planets in the night sky.