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be (living) on another planet

slang To be oblivious to one's surroundings or act strangely. I have no idea what the professor said during today's lecture because I was on another planet the whole time. The millionaire investor always says something wacky in the board meetings—it's like he's on living another planet.
See also: another, on, planet

What planet is (someone) on?

What are you thinking? That is an absurd or stupid thing to think or do. (Implies that someone would only do or think that if they were an alien from another planet.) A: "I think they should just do away with taxes altogether!" B: "What planet are you on? Taxes pay for hospitals, roads, our military—literally everything on which our society is built." What planet is he on? He could get someone killed driving that speed along a residential road!
See also: planet, what

what planet is someone on?

COMMON You can say what planet is someone on? to show that you think someone has crazy ideas or does not know about something that most people know about. What planet are these people on? Do they not read their own headlines? Note: This expression is often varied. For example, you can ask what planet does someone live on? or what planet does someone come from?. He thinks hospitals can make major cuts to their budgets. What planet does he live on? Note: You can also say that someone is on another planet. She was just on another planet, I think. She didn't seem to understand that we are ordinary people.
See also: planet, someone, what

what planet are you on?

used to indicate that someone is out of touch with reality. British informal
See also: planet, what

be on another ˈplanet


what ˈplanet is somebody on?

(spoken, humorous) used to suggest that somebody’s ideas are not realistic or practical: He can’t really think we’re going to finish the job today, can he? What planet is he on?
See also: another, on, planet
References in classic literature ?
His idea was that meteorites might be falling in a heavy shower upon the planet, or that a huge volcanic explosion was in progress.
Dense clouds of smoke or dust, visible through a powerful telescope on earth as little grey, fluctuating patches, spread through the clearness of the planet's atmos- phere and obscured its more familiar features.
I remember how jubilant Markham was at securing a new photograph of the planet for the illustrated paper he edited in those days.
Results of these earthbound investigations have implications for explorations of other planets. On Mars, a desert planet where dust devils are common and unusually large, the whirlwinds result from severe atmospheric turbulence.
Now, astronomers have given another dwarf planet an official name.
That means that in 2011, this planet will have completed one orbit since its discovery in 1846.
Summary: TEHRAN (FNA)- A new study provides the most accurate estimate of the frequency that planets that are similar to Earth in size and in distance from their host star occur around stars similar to our Sun.
Just because a planet is rocky, doesn't mean it is similar to Earth and capable of supporting life.
The levels would not be as high as those in a pulsar's disk, but any increase in heavy elements could affect planet formation: on one hand, gas planets form more readily around metal-rich stars; on the other hand, rapid gas dispersion might keep the disk's mass low, making it difficult to produce gas giants.
NASA on Wednesday confirmed a bonanza of 715 newly discovered planets outside the solar system.
In the meantime, astronomers have observed the blue planet with telescopes on Earth and in space.
But last August, the International Astronomical Union approved the first formal definition of a planet since the Greeks coined the term some 2,000 years ago.
Which planet's average temperature is roughly 380 degrees Fahrenheit colder than Earth's?
When scientists first spotted Pluto in 1930, they labeled it a planet because it appeared similar to other planets.
Embedded Planet offers a full line of small form factor PC/104, EBX, and credit-card-sized single-board computers based on Motorola's PowerQUICC 8xx and PowerQUICC II 82xx processors, and IBM Microelectronics' PowerPC 405GP processors.