The night sky is full of light, most of which is produced by celestial bodies, such as stars and planets. If you can't tell the difference between the celestial bodies visible in the sky, try to begin to identify the physical characteristics of the stars and planets, and when is the best time to see them.
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Part 1 of 3: Paying attention to Physical Differences
Step 1. See if the celestial body is twinkling
One of the easiest ways to tell the difference between a planet and a star is to look for a twinkle or glow in the related celestial body. These twinkles are usually visible to the naked eye if you can see the night sky clearly enough and stare at the sky long enough.
- Stars twinkle and glow. This is why there is a song called "Twinkle, Twinkle Little Star".
- Planets don't twinkle. The brightness of the planet and its overall appearance in the night sky remains the same.
- When viewed through a telescope, the planet's surroundings appear to be "rippled".
- Anything that twinkles, sparkles, or glows is most likely a star. However, this light also comes from a fast-moving plane in the night sky.
Step 2. Watch as the object rises and sets
The location of celestial bodies is not fixed in the night sky. All celestial bodies move, but the way they move can tell the difference between stars and planets.
- Planets rise in the east and set in the west because they tend to follow the course of space throughout the night like the sun and moon.
- Stars move in the night sky, but neither rise nor set. Instead, the stars orbit in a circular pattern around Polaris (the North Star).
- If the celestial body you see appears to be moving in more or less straight lines across the night sky, it is likely a planet.
- Satellites also move through the night sky, but much faster than planets. A planet takes hours to weeks to cross the night sky, whereas a satellite can move beyond sight in minutes.
Step 3. Identify the ecliptic
Planets are always found along an imaginary belt along the sky called the ecliptic. The belt isn't really visible, but careful observation will help you identify where the celestial bodies are gathering. Although stars can also appear along this imaginary belt, you should be able to tell them apart by their visible glow.
- Of all the celestial bodies along the ecliptic, Mercury, Venus, Mars, Jupiter, and Saturn appear much brighter than the surrounding stars. This is because the distance of these planets is closer to the sun so that the reflected light is brighter.
- The easiest way to find the ecliptic is to note the location and path of the moon and sun in the sky relative to your location on earth. The path of the sun across the sky is very close to the path of the planets along the ecliptic.
Step 4. Monitor the color of the celestial body
Not all planets have color. However, many of the most clearly visible planets in our night sky have color. This can help distinguish planets from stars. Although some people with sharp eyes are able to spot these color differences, they usually range from bluish-white to yellowish-white. To most people, stars appear white to the naked eye.
- Mercury is usually gray or slightly brown in color.
- Venus looks pale yellow.
- Mars is usually a color between pale pink and bright red. This is influenced by the relative brightness or dimness of the planet Mars, which changes in a two-year cycle.
- Jupiter appears orange with white circles.
- Saturn appears pale gold in color.
- Uranus and Neptune appear pale blue. However, they are usually invisible to the naked eye.
Step 5. Compare the relative brightness levels
Although planets and stars both glow in the night sky, planets usually appear much brighter than stars. Astronomers measure the relative brightness of celestial bodies using astronomical size scales, and most planets fall into the category of being easy to see with the naked eye.
- Planets reflect bright light from the sun, which is quite close to the earth. Instead, the star emits its own light.
- Although most stars are brighter and larger than the sun, these stars are much farther from Earth than the planets in our solar system. Therefore, planets (which reflect sunlight) usually appear brighter when viewed from Earth.
Part 2 of 3: Observing Celestial Bodies
Step 1. Bring a star chart and planetary guide
Whether you have poor night vision or are simply confused about the exact location of a particular celestial body, this chart or guide can help you find it. You can buy star charts and planetary guides in bookstores, print free instructions from the internet, or download an astronomy app on your phone.
- Note that star charts are usually only valid for a limited time (usually a month) because the position of the stars in the sky changes as the earth rotates in its orbit.
- If you are using a star chart or planetary guide in the field, be sure to use a dim red flashlight. This flashlight is designed to emit light without affecting the eye's ability to adjust to darkness.
Step 2. Get a good telescope or binoculars
If looking at the stars with the naked eye is not enough to see celestial bodies clearly, you should consider buying a telescope or binoculars. Both of these tools can help you zoom in on the area you want to observe. Thus, objects can be seen more clearly and even reveal celestial bodies that previously escaped the naked eye.
- Some experts suggest getting used to seeing celestial bodies with the naked eye, then continued with binoculars, and finally switching to a telescope. This method helps the eye get used to seeing celestial bodies and their location in the night sky.
- Compare telescopes and binoculars on the internet before buying. Read reviews from owners of the model telescope or binoculars you want.
Step 3. Visit the night sky site
Light pollution in residential areas can greatly reduce the visibility of celestial bodies in the night sky. To fix this, try visiting the night sky site. In the United States, these particular sites are identified by the International Dark-Sky Association (IDA) as protected from light pollution and urban development.
- Common night sky sites include city or national parks, although other night sky sites are usually surrounded by well-lit and developed areas.
- If you live in the United States, try checking the IDA website to find a night sky site near where you live.
Part 3 of 3: Identifying Perspective Limiting Factors
Step 1. Check if there will be an occultation in the near future
Occultation is when the moon passes between Earth and a related star or planet, blocking the view of a celestial body. These obstacles occur fairly regularly and can be planned because their occurrence is predictable.
- Occultations can be seen from some locations on earth, and some are not. Check beforehand to see if the view of the night sky is severely affected.
- You can find an occultation schedule by searching the internet or consulting an astronomy guide. An institution called The International Occultation Timing Association publishes its estimates on the internet for free.
Step 2. Identify the phases of the moon
The light reflected by the moon can block the view of stars or planets. If the moon is in or near the full phase, celestial bodies will be difficult to see. Therefore, it is a good idea to check the phase of the moon before planning a night sky viewing event.
If you don't know the current phase of the moon, check it out online for free. The Meteorology, Climatology and Geophysics Agency website provides a schedule of the phases of the moon in each year
Step 3. Find the right conditions
Knowing how to tell the difference between stars and planets has no significant impact if the night sky cannot be seen. Your ability to see celestial bodies can be limited by several factors, both man-made and natural
- Light pollution is the biggest limiting factor. If you live in a metropolitan area, you may need to go to a more remote area to get a clearer view of the night sky.
- Heavy clouds and snow can greatly affect visibility of the night sky. If the weather is very cloudy or the ground is covered with heavy snow, it is likely to be difficult to see celestial bodies in the sky.
Step 4. Avoid other limiting factors
There are many other factors that affect the ability to see the night sky, including self-inflicted ones. For example, the level of alcohol consumption, nicotine consumption, and pupil dilation when looking at the night sky. All of these factors can affect the eye's ability to adjust to darkness, and to recognize stars and planets in the night sky.
