What planets are visible tonight?
Some of the best views in astronomy actually come from the planets and not stars. So, while it’s understandable that you probably want to view the faraway stars and nebulae, don’t forget that the planets of our solar system—that are relatively close— can be great objects to find and observe.
All of the 7 planets (not counting our Earth) in our solar system are technically visible depending on your location, however, there are five special planets that we can observe with just the naked eye: Mercury, Venus, Mars, Jupiter, Saturn.
Uranus and Neptune, the two outer planets, can be barely visible depending on your location. However, even when they are visible, they’ll look identical to stars. You’d need a good telescope or a good pair of binoculars to properly observe these outer planets.
Here, we will learn together about which planets are visible tonight, and where to look for them. Before we begin, however, it helps to understand that observing planets has several unique things to consider as opposed to observing stars or other deep space objects.
Planet Observation: Why Planets Have Different Observing Times
Unlike stars, planets don’t follow a simple cycle and different planets in our solar system have different cycles. When the planets appear is dictated by their own rotational period (time to orbit the sun). Mercury, for example, has a 88 days rotational period, but Saturn needs 29 years to fully orbit the Sun.
So, every January, for example, these planets can have different positions in relation to the Sun and the Earth, and so some planets might be observable in January 2020, but won’t be available in January 2021.
With that being said, if you want to observe stars, make sure you are looking at the right calendar.
Planet Observations: The Best Time to Observe a Planet
The above image will explain the best time to see the different planets, but we have to delve further before we can explain it properly.
As mentioned, we are going to mainly focus on the five ‘visible’ planets, and we can further divide these planets into two groups:
- Inferior planets: planets that lie inside our Earth’s orbit and are closer to the sun. Mercury and Venus belong to this category.
- Superior planets: planets that lie outside our Earth’s orbit and are further from the sun. Mars, Jupiter, and Saturn belong here.
The Best Time To See Inferior Planets
Since, as mentioned, Mercury and Venus performed their rotations inside the path of the Earth’s orbit, there are several things we must consider:
- Mercury and Venus orbit faster than the earth, they do their rotation in 88 days and 225 days respectively. So, they change position very quickly and you have smaller windows to observe them.
- Because we can see parts of the planet facing away from the sun, and so they have phases, called the planetary phase, just like the moon. So, we can only see them in full at certain times.
In general, the best time to see the inferior planets is during their western and eastern greatest elongations, as you can see in the image above.
On the other hand, the worst time to observe these inferior planets is when they are in conjunction. In the image above we can see that there are inferior conjunction and superior conjunction. It’s important to note that they don’t mean conjunctions for inferior and superior planets, respectively, instead:
- Superior conjunctions are conjunctions that happen when the planet is on the opposite side of the sun in comparison with the earth’s position
- Inferior conjunctions, on the other hand, are when the planet is positioned between the earth and the sun
The inferior planets can’t be observed when they are at (and near) conjunctions since they are going to be obscured by the sun’s glare.
However, a very rare occasion is when the planet is on the same plane as the earth and the sun, and inferior conjunction happens. In this rare case, we can see a mesmerizing view of the planet (Venus and Mercury) to pass in front of the sun.
Sadly this occasion called Transit of Venus is sill 97 years in the future, and for Mercury, we still need to wait until 2032.
The Best Time To See Superior Planets
Mars, Jupiter, and Saturn (and also Uranus and Neptune) make their rotations outside the earth’s orbit. So, there have different characteristics compared to Mercury and Venus:
- As expected, they take longer to complete their rotation period, and so they move slowly across the celestial sphere. That is, parallax-wise, these planets only move a short distance compared to the stars in their background.
- Since the earth is inside the orbit, we can only see the side facing the sun. So, they don’t have phases and we will always see them in full.
The best time to see these superior planets is at opposition, not elongation. If we see again at the image above, the superior planets never pass between the Earth and the sun. So, at the opposition, we sit directly between the planet and the sun. So, they won’t be obstructed by the sun’s glare.
The planet during their opposition is visible all night long and is transiting (highest positioned) around midnight.
What Planets are Visible Tonight?
If you want to check what planets are visible tonight, then you can check the two tables below. These tables show which of the five planets can be seen tonight in each month of 2020 and 2021.
Before we explain them month-by-month, here are a bit of explanations for the terms we use in the tables:
- -: not observable, mainly because the planet is too close to the sun.
- Dusk: the planet is visible in the western sky after sunset (around an hour or so). For Venus and Mercury, a bold dusk indicates the month when greatest eastern elongation (the best time to view them) takes place. Since elongation for mercury only happens for a very short time, dusk (early) indicates that elongation happens at the early part of the month, dusk (middle) indicates the middle part of the said month, and dusk (later) indicates the later part of the month.
- Dawn : the planet is visible in the eastern sky before sunrise (around an hour or so). For Venus and Mercury, a bold dusk indicates the month when greatest western elongation (the best time to view them) takes place. Since elongation for mercury only happens for a very short time, dawn (early) indicates that elongation happens at the early part of the month, dawn (middle) indicates the middle part of the said month, and dawn(later) indicates the later part of the month.
- Morn: the planet is best seen in the Morning sky, after midnight and before dawn. The planet reaches its highest possible point in the celestial sphere when it crosses the meridian (due North in the Southern hemisphere, due South in the Northern hemisphere) during the Morning.
- Eve: the planet is best seen in the evening sky, after dusk but before midnight. The planet reaches its highest possible point in the celestial sphere when it crosses the meridian (due North in the Southern hemisphere, due South in the Northern hemisphere) during the evening or late afternoon.
- ALL: the planet can be seen all night long from dusk to dawn, at least for most of the night. The planet reaches the highest point in the celestial sphere within an hour before or after midnight. For superior planets, ALL indicates that the planet’s opposition occurs in this month.
Keep in mind that even at their best time of viewing, the planets may not be visible depending on your latitude, weather for the night, the planet’s current magnitude, and various factors affecting the sky’s condition.
Month-by-Month Details: Planets Visible Today
We hope this guide can help you make the most of your 2020 stargazing and planet observation plan. The five visible planets, and also Uranus and Neptune all put out unique and spectacular views at various points in 2020.
Obviously, each offers its own challenges, so it’s best to prepare ahead and get the best astronomy equipment before you set to observe the planets.
Again, view Mercury and Venus when they are at their greatest elongation, as listed in the above calendar. For Mars, Jupiter, and Saturn, the best time is to view them at opposition:
- Mars: October 14th
- Jupiter: July 14th
- Saturn: July 20th
- Uranus: October 31st
- Neptune: September 11th