Starting in 1914, Gustav Holst was compelled to compose a series of movements that embody the essence of the celestial masses of rock in our nearby space real estate. They're some of the most renowned and enduring compositions to this day that have influenced popular culture ("Mars" was a primary inspiration for Star Wars infamous Imperial March, Darth Vader's theme). Hans Zimmer was inspired by "Mars" when composing the soundtrack for Gladiator, but he flew a little too close to the sun and was sued for Copyright Infringement by the Holst Foundation. The compositions weren't fully performed as a whole until years later in 1920, when Albert Coates conducted the London Symphony Orchestra.
Holst himself was a composer/arranger/teacher from the UK whose biggest accomplishment was The Planets, but he was a frequent creator with works spanning across a multitude of genres. When he was developing as a young composer, he was greatly influenced by those who came before him such as Richard Strauss and Richard Wagner, and motivated by his contemporary Maurice Ravel. I love Ravel's work too so I'll be doing a write up on him coming soon!
The idea to compose this movement came when Holst was hanging out with an English writer, Clifford Bax, on a Spanish Island on vacation. He introduced Holst to the concept of Astrology and Holst became slightly obsessed with the newfound concept shortly after. The songs were first scored all on piano, excluding "Neptune" which utilized an organ. Holst thought about it, and thought the piano had too many percussive elements to be appropriate for compositions derivative of our planets, so he adopted a large orchestra shortly after.
The Hollywood Bowl
Source
These compositions are incredible. They capture the soul of each planet/astrological sign but also introduce you to new thoughts and feelings that totally make sense on the 4th or 5th listen. I was lucky enough to catch a performance of these movements in 2014 conducted by Gustavo Dudamel of the Los Angeles Philharmonic at the historic Hollywood Bowl. While they were performing each song they had a screen that showed official NASA images of each planet being featured. Me, my cousin 
Below you'll find each movement. I hope you can put these on in the background while you're working on something or have the time to sit down and listen. It's an amazing soundtrack for a backyard fire pit,
Gustav Holst - Mars, the Bringer of War
A dark, heavy leadoff. As mentioned above, has influenced a number of popular scores/composers such as John Williams with Star Wars and Hans Zimmer with Gladiator. The war drums and gradual build make it feel like you're marching into battle. Listening can probably remind you of other war songs in movies that sound vaguely similar. About two and a half minutes in I can really hear its influence on other Star Wars compositions other than the Imperial March.
Gustav Holst - Venus, Bringer of Peace
One of my personal favorites. Probably the most serene of the bunch....the beginning just feels like a leaf falling peacefully from a tree and swaying side to side. The spotlight they bring on the violin two minutes in is just unfiltered bliss. There's a part about 3:30/4 minutes in that reminds me so much of the incredibly emotional To Kill A Mockingbird theme song
Gustav Holst - Mercury, The Winged Messenger
The "Winged Messenger" is right. The wind instruments hopping back and forth make this feels like a graceful bird is mid flight. But around a minute in the dynamic changes into a beautiful crescendo slowly incorporating all instruments into the grand climax.
Gustav Holst - Jupiter, Bringer of Jollity
The most grandiose of the bunch. It feels like an opened world, wind in your face start of an adventure. Positive and powerful, and inspiring call to arms. Also a fantastic drinking song. About 2:50 in there's a total mood change, and it feels like you've just won a battle in the dead of night, and the sun is coming up with blood on your face. You and your friends made it out alive.
Gustav Holst - Saturn, Bringer of Old Age
Introspective and understated. Existential, pondering our mortality and purpose. This one wasn't a favorite from the get-go but after several listens its just as amazing as every other. Lord Of The Rings may have been inspired by elements of the very beginning of this song, in the song where they recount how the ring was made. Check out the song here for comparison.
Gustav Holst - Uranus, The Magician
I swear I hear this songs influence of Disney's Fantasia when Mickey is working for the Magician. Especially when Mickey makes the broomstick carry the water for him here. Especially how the song gets increasingly stressful as later in the scene things start going haywire for Mickey. The mood changes at a little of a minute and a half in, turns into a triumphant then reflective anthem.
Gustav Holst - Neptune, The Mystic
The final part of the movement. This one's a little quiet so you'll have to turn it up. It sounds the spaciest to me, like someone looking up at the stars wondering about our planets and solar system. You have to check out the part at 4:45...when the choral voices come in is one of the most beautiful parts of this entire series of movements.
