Whichever way you look, the night sky is full of lights. Some of these are generated by the stars that glow in the dark; other celestial bodies, such as planets, reflect the light of the Sun by appearing "bright" in the night sky. If you can't tell if a celestial object is a star or a planet, you can learn to recognize its different physical characteristics. You can make the process even easier by maximizing the visibility of the sky.
Steps
Part 1 of 3: Observing Physical Differences
Step 1. Check if the celestial body is sparkling
One of the simplest ways to tell stars from planets is to see if the object sparkles or glitters. If you have a good view of the sky and observe it long enough, you can usually see this feature with the naked eye.
- The stars twinkle and sparkle.
- The planets do not emit any sparkles; their light remains constant just like their general appearance in the night sky.
- If you look at them through a telescope, the edges of the planets seem to "wobble".
- Any celestial object that glitters, glitters or sparkles is probably a star; however it could also be a plane moving fast in the sky.
Step 2. Observe if the bright object rises and sets
The celestial bodies are not stationary in the sky, they all move, but the way they do it is a good indicator of whether they are stars or planets.
- The planets rise in the east and set in the west; they tend to follow a similar path to that of the Sun and the Moon.
- The stars move in the sky but do not rise and do not set; instead they follow a circular orbit around Polaris (the North Star).
- If the celestial object appears to be moving more or less in a straight line in the sky, it is likely a planet.
- Satellites also move in the night sky, but they are much faster than planets; the latter take hours or even weeks to follow their own trajectory, while a satellite does so in a few minutes.
Step 3. Identify the ecliptic
The planets are always found along an imaginary belt of the sky called the ecliptic; this band is not a visible object, but with careful observation you are able to recognize the area in which the celestial objects are gathered. Although stars can also make an appearance inside this belt, they are recognizable by their shimmering appearance.
- Among the celestial bodies found along the ecliptic, Mercury, Venus, Mars, Jupiter and Saturn are much brighter than the surrounding stars; this phenomenon is due to their proximity to the Sun, since the "brightness" of the planets is simply the reflected sunlight.
- The easiest way to find the ecliptic is to note the position and trajectory of the Sun and Moon in the sky relative to the observer's position on Earth. The solar path in the sky is very similar to that of the planets along the ecliptic.
Step 4. Evaluate the color
Not all planets are colored; however, many of the main ones that you can see in the night sky have some sort of coloring; this feature allows you to distinguish them from the stars. Although some individuals with exceptional eyesight are able to perceive slight differences in tint, coloration generally falls within the bluish and yellowish spectrum; for most people, stars are white when viewed with the naked eye.
- Mercury is typically gray or brownish.
- Venus has a pale yellow color.
- Mars shows shades ranging from pale pink to bright red; this effect is due to the greater or lesser brightness of the planet which varies over a two-year cycle.
- Jupiter is orange with white bands.
- Saturn usually has a pale golden color.
- Uranium and Neptune are light blue in color, but they are not visible to the naked eye.
Step 5. Compare relative brightness
Although the planets and stars are both bright in the night sky, the former appear much brighter than many stars. Astronomers measure the relative brightness of celestial bodies using the apparent magnitude scale, according to which most planets fall within the range of bright objects that are easily visible to the naked eye.
- The planets reflect the light of the star of our solar system (the Sun) which is relatively close to the Earth; instead the stars shine with their own light.
- Although some stars are much brighter and larger than the Sun, they are also much further away from us than the planets that make up the solar system; for this reason, planets (which reflect sunlight) are typically brighter when viewed from Earth.
Part 2 of 3: Observe the Heavenly Bodies
Step 1. Bring a celestial map and a planetary guide with you
When night visibility is not good or you simply have doubts about the position of certain celestial bodies, a map or a guide will help you recognize what you are observing. You can buy these instruments in the library, print them for free from the web or download star / planetary guides in the form of smartphone applications.
- Remember that star maps are only valid for a period of time (typically a month) because the position of the stars in the sky changes as the Earth travels its orbit.
- If you consult the map or the guide in the countryside, bring a small flashlight of red light that is not too intense; these torches provide enough light to read without affecting the human eye's ability to adapt to the dark.
Step 2. Get a good telescope or binoculars
If viewing with the naked eye isn't enough for your needs, you can consider buying a telescope or binoculars. These tools improve your vision by enlarging the area of your interest; you can observe visible objects more clearly and be able to identify those invisible to the naked eye.
- Some experts recommend getting familiar with celestial bodies without any tools, then you can move on to binoculars and finally telescopes. This process allows you to know the presence and position of visible objects in the night sky.
- Compare the various telescopes and binoculars online before purchasing; do a web search and read reviews written by people who already own that particular model.
Step 3. Go to an observatory
The light pollution of urban centers drastically reduces the ability to see celestial bodies; to maximize visibility, you need to go to a protected area which is usually close to the observatories. These sites have been identified and recognized by the International Dark-Sky Association (IDA) as protected spaces from urban development and consequent light pollution. In Italy there is a similar initiative called "Parchi delle Stelle", follow this link for more details.
- Typically these sites are found in national and regional parks, nature reserves and near astronomical observatories.
- Search online to find out which area is closest to you.
Part 3 of 3: Identify the Factors Limiting Visibility
Step 1. Check if a concealment is expected
This is the phenomenon whereby the Moon intervenes between the Earth and a certain star or planet, preventing its observation. Occultations occur with some regularity and can be planned because they are predictable.
- They may be visible from some locations on Earth and not from others; check ahead to see if one is expected and if it can significantly alter your visibility.
- To do this, you can do an online search or consult an astronomical guide. The site of the Italian Amateur Astronomers Union provides almanacs with the phenomena expected for the current year and which you can download for free.
Step 2. Identify the moon phase
The light reflected from the Moon can prevent you from seeing the stars and planets. If you are close to the full moon, you may have difficulty observing celestial bodies; for this reason, it is best to check the current moon phase before venturing outdoors for a night of observing.
If you are not sure about the current moon phase, you can consult an online guide for free; just type the words "current moon phase" in any search engine or consult the site of the Italian Amateur Astronomers Union. The US Navy website allows you to check the moon phases by date up to 2100
Step 3. Find the correct observation conditions
Being able to distinguish stars from planets is not very useful if the visibility of the sky is poor. The ability to see celestial bodies is influenced by several factors, some natural and others attributable to man.
- Light pollution is one of the most important factors limiting the visibility of the night sky; if you live in an urban area, you probably need to move to a rural area to better observe celestial bodies.
- Clouds and abundant snow cover the possibility of exploring the night sky; if there are a lot of clouds or a lot of snow on the ground you may have great difficulty seeing celestial bodies.
Step 4. Avoid the other limiting factors
There are other elements that contribute to a bad view of the night sky, some of which are up to you. For example, the consumption of alcohol, nicotine and pupillary dilation at the time of observation alter the vision; these factors modify the ability of the eyes to adapt to the dark and therefore recognize stars from planets.
