Why is Mars sometimes bright? But not in October 2021

Chart showing Earth and Mars on opposite sides of the sun.
Earth and Mars round October 7-8, 2021. That’s when Mars is in conjunction with the solar. It’s passing behind the solar from Earth and may’t be seen in our sky. Picture by way of CyberSky.

Why is Mars typically vibrant?

2020 was a very good yr to view Mars. For a part of that yr, Mars appeared as a blazing pink dot of flame in our night time sky. However, though Mars began this yr shining brightly, it rapidly pale. And it went on to seem fairly dim all through 2021. Then, in August, Mars disappeared into the sundown. Mars’ conjunction with the solar comes on October 8, 2021 (4 UTC). Now – in early October, 2021 – Mars is fully gone from our sky. It’s touring throughout the sky with the solar in the course of the day. However Mars will return earlier than 2021 ends. It’ll seem within the east earlier than dawn in late November, to begin a brand new cycle of visibility and a a lot better yr in 2022.

Mars’ dramatic swings in brightness are a part of the rationale the early stargazers named Mars for his or her god of war. Generally the warfare god rests. And typically he grows fierce!

So … why? Why is Mars vibrant in some years, however faint in others? And what can we count on from the pink planet for the remainder of 2021, and for 2022? For specifics on Mars within the coming months, bookmark EarthSky’s monthly planet guide.

Want photos of Mars at its best in 2020? Click here.

Wish to perceive why Mars is usually vibrant and typically faint? Maintain studying, to be taught why Mars is without doubt one of the most fascinating planets to look at.

Why is Mars sometimes bright: Moon and Mars rising above a ridgeline, with a glorious display of green northern lights filling most of the sky.
View at EarthSky Community Photos. | Why is Mars typically vibrant? Abigail Atienza caught the waning gibbous moon and pink planet Mars (on the best) with the northern lights alongside the Street to Nowhere, Iqaluit, Nunavut, Canada, on September 6, 2020. Thanks, Abigail. See extra photos of Mars at its closest in 2020.
Orange ball with dark markings and white spot at the pole.
View at EarthSky Community Photos. | Nancy Ricigliano captured Mars from Lengthy Island, New York, on October 6, 2020, when it was closest to Earth. Thanks, Nancy. See extra photos of Mars at its closest in 2020.

Mars isn’t very huge

To grasp why Mars varies a lot in brightness in Earth’s sky, first notice that Mars isn’t a really huge world. It’s solely 4,219 miles (6,790 km) in diameter, making it solely barely greater than half Earth’s dimension (7,922 miles or 12,750 km in diameter).

Take into account Mars in distinction to Jupiter, the largest planet in our photo voltaic system. Jupiter is 86,881 miles (140,000 km) in diameter. Greater than 20 planets the scale of Mars could possibly be lined up facet by facet in entrance of Jupiter. Jupiter all the time appears vibrant, as a result of it’s so huge.

Not so for little Mars. Its extremes in brightness must do with its nearness (or lack of nearness) to Earth.

Double photo with large Earth on left and smaller Mars on right, to scale.
Mars isn’t very huge, so its brightness – when it is vibrant – isn’t attributable to its bigness, as is true of Jupiter. Mars’ brightness, or lack of brightness, is all about how shut we’re to the pink planet. It’s all about the place Earth and Mars are, relative to one another, of their respective orbits across the solar. Picture by way of Lunar and Planetary Institute.
Long exposure photo with big dot of Mars and its reflection in a lake, and Milky Way soaring above.
Matt Pollack captured Mars from Little Tupper Lake within the Adirondacks of upstate New York in July 2018. Read more about this photo.

Mars orbits one step outward

Mars orbits the solar one step outward from Earth. The distances between Earth and Mars change as each worlds orbit across the solar. Generally Earth and Mars are on the identical facet of the photo voltaic system and close to each other. Generally, as was the case for a lot of 2019 and would be the case for a lot of 2021, Mars and Earth are on practically reverse sides of the solar from one another, and so Mars seems faint.

Take a look at the illustration beneath, which views the photo voltaic system from above. After which have a look at the illustration on the high of this submit. The illustration at high reveals Earth and Mars of their respective positions of their orbits across the solar in October 2021. Keep in mind, Mars comes most practically to passing behind the solar from Earth on October 7-8. The illustration beneath reveals Earth and Mars as they are going to be across the time of Mars’ 2022 opposition on December 4. At the moment, Earth might be passing between the solar and Mars. And Mars might be closest and brightest for all of 2022.

Chart showing Earth passing between the sun and Mars.
Earth and Mars round December 8, 2022. Earth is passing between Mars and the solar. Mars is reverse the solar – at what astronomers name opposition. Thus Mars might be rising within the east at sundown, highest at midnight and setting at daybreak. Picture by way of CyberSky.

Why is Mars typically vibrant?

Earth takes a yr to orbit the solar as soon as. Mars takes about two years to orbit as soon as. Opposition for Mars – when Earth passes between Mars and the solar – occurs each two years and 50 days.

So Mars’ brightness waxes and wanes in our sky about each two years. However that’s not the one cycle of Mars that impacts its brightness. There’s additionally a 15-year cycle of vibrant and faint oppositions.

Because of that 15-year cycle, 2018 was a really, very particular yr for Mars, when the planet was brighter than it had been since 2003. Astronomers known as it a perihelic opposition (or perihelic apparition) of Mars. In different phrases, in 2018, we went between Mars and the solar – bringing Mars to opposition in our sky – across the identical time Mars got here closest to the solar. The phrase perihelion refers to Mars’ closest level to the solar in orbit.

Possibly you possibly can see that – in years once we move between Mars and the solar, when Mars can be closest to the solar – Earth and Mars are closest. That’s what occurred in 2018.

2003 was the earlier perihelic opposition for Mars. The pink planet got here inside 34.6 million miles (55.7 million km) of Earth, nearer than at any time in over practically 60,000 years! That was actually one thing.

In 2020, Mars was nonetheless very vibrant at opposition. Nevertheless it wasn’t as vibrant because it had been in 2018, or in 2003.

When is the following opposition of Mars? The subsequent time Mars will seem at its brightest for that two-year interval in our sky? You guessed it. 2022!

Earth's and Mars' orbits with Mars in different sizes at different points around its orbit.
There’s a 15-year cycle of Mars, whereby the pink planet is brighter and fainter at opposition. In July 2018, we had been on the peak of the 2-year cycle – and the height of the 15-year cycle – and Mars was very, very vibrant! In 2020, we had been additionally on the peak of the 2-year cycle; nonetheless, Earth and Mars had been farther aside at Mars’ opposition than they had been in 2018. Nonetheless, 2020’s opposition of Mars was glorious. Diagram by Roy L. Bishop. Copyright Royal Astronomical Society of Canada. Used with permission. Go to the RASC estore to buy the Observer’s Handbook, a vital device for all skywatchers. Read more about this image.

Backside line: Mars alternates years in showing vibrant and faint in our night time sky. 2020 introduced one other vibrant yr for Mars. However, in 2021, Mars has been principally faint and inconspicuous. Why?

Photos of bright Mars in 2018, from the EarthSky community

Photos of bright Mars in 2020, from the EarthSky community | Why is Mars typically vibrant? However not in October 2021


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