This is the archive for the BAFacts — short science factoids — I post every day on Twitter and Google+ . I introduced this new feature on January 4, 2012 to coincide with perihelion, because I’m a dork.

January 4, 2012: At 01:00 GMT tonight, the Earth is closest to the Sun for the year: 147,097,207 km. http://is.gd/uitrIT

January 5, 2012: There are no green stars. is.gd/J8vDR9

January 6, 2012: While there aren’t green stars, there *are* green objects in space! is.gd/6goWkE

January 7, 2012: When 3 celestial bodies align, like in an eclipse, it’s called a “syzygy”. That’s 23 pts in Words w/ Friends!

January 8, 2012: Earth has aurorae, but other planets do too. For Jupiter, its moons play a role: http://is.gd/z3atQW

January 9, 2012: It would take almost 9 years to walk to the Moon. If there were a road 400,000 km long.

January 10, 2012: There are 88 official constellations, the same number as keys on a piano. To know them all, you’d better C#.

January 11, 2012: There’s no real definition of how far over your head the sky starts.

January 12, 2012: On the surface of a neutron star, the gravity is so strong you’d weigh several *billion* tons.

January 13, 2012: There are hundreds of billions of planets in our galaxy. Hundreds of *BILLIONS*! http://is.gd/aELYcH

January 14, 2012: Four planets in the solar system have rings: Jupiter, Saturn, Uranus, and Neptune. http://is.gd/nKwuWH

January 15, 2012: Mars is red due to the presence of large amounts of iron oxide: rust! http://is.gd/asOy7V

January 16, 2012: Over 500 people have flown into space – about 0.000007% of the world’s population.

January 17, 2012: The common definition of where “space” starts – the Kármán line – is 100 km above the Earth. http://is.gd/jsH1Ka

January 18, 2012: Websites are dark today to protest SOPA. The Universe is dark because it’s not infinite. http://is.gd/BRfJ4P

January 19, 2012: The first stars in the Universe formed about 400 million years after the Big Bang. http://is.gd/7KG7PH

January 20, 2012: The Earth is warming up. http://is.gd/Sns3sl

January 21, 2012: Cumulatively, astronauts have spent more 77 years in space: about a human lifetime. http://is.gd/qmRZq0

January 22, 2012: Every time a comet goes around the Sun, it dies a little bit. is.gd/NIfvBG

January 23, 2012: The Earth is 3.7x the Moon’s diameter, 50x its volume, and 81x its mass.

January 24, 2012: A green aurora is due to emission from oxygen atoms high in the air as their electrons give up energy. http://is.gd/GZTQb1

January 25, 2012: The Moon does not cause major – or even moderate – earthquakes. http://is.gd/CdReNT

January 26, 2012: Brown dwarfs aren’t brown. They’re red. Really, really red. http://is.gd/m23UtJ

January 27, 2012: If you stand on your tiptoes, the horizon is about 5 km (3 miles) away. http://is.gd/vhK9lG

January 28, 2012: Pluto is smaller than our own Moon, yet has (at least) four moons of its own. http://is.gd/ChIVVO

January 29, 2012: The core of the Sun is 15 million degrees Centigrade – that’s 27 million degrees F.

January 30, 2012: By combining three equations, you can describe the overall evolution of the Universe.http://is.gd/5L1HkD

January 31, 2012: The Moon orbits the earth at a velocity of about 1 km/sec, roughly as fast as a rifle bullet.

February 1, 2012: In 1st moments after the Big Bang, only hydrogen, helium, & a dab of lithium were made. Everything else came later.

February 2, 2012: A complete cycle of day and night is called a nychthemeron. How about that?

February 3, 2012: At least 158 gorgeous stellar beehives called globular clusters orbit our galaxy. is.gd/I2PYS7

February 4, 2012: Dry ice evaporating on the surface of Mars in spring can trigger avalanches, and we have pictures! http://is.gd/MvZzTt

February 5, 2012: Impacts can eject material that makes long lines of secondary impacts called crater chains. http://is.gd/u3pDoG

February 6, 2012: Most asteroids are shaped like potatoes. Kleopatra is shaped like… a dog bone. http://is.gd/beJJC9

February 7, 2012: Centrifugal force is just as real as centripetal acceleration. It only depends on your view. http://is.gd/RmBU0x

February 8, 2012: Many comets have two tails: one dust, one gas. And they’re different colors! http://is.gd/SEKsyA

February 9, 2012: Astronomers have seen a star eaten by a black hole. http://is.gd/61G0Za

February 10, 2012: The background glow of the Big Bang can still be seen, even after 13.73 billion years. http://is.gd/7KG7PH

February 11, 2012: Venus may still have active volcanoes on its surface. http://is.gd/wU62Do

February 12, 2012: Saturn has weird moons. Iapetus is shaped like a walnut. http://is.gd/AExJiT

February 13, 2012: Saturn has weird moons. Hyperion is like a Styrofoam ball that’s been punched a zillion times. http://is.gd/tjgHhY

February 14, 2012: Saturn has weird moons. Mimas is the Death Star. http://is.gd/mtDg4u

February 15, 2012: Saturn has weird moons. Mimas looks like Kenny. http://is.gd/AKupL

February 16, 2012: Saturn has weird moons. Mimas looks like Pac-Man. http://is.gd/FcWqtV

February 17, 2012: Saturn has weird moons. Every four years, Janus and Epimetheus swap orbits! http://is.gd/Pq2eyf

February 18, 2012: Saturn has weird moons. Some of the water erupting from geysers on Enceladus falls on Saturn. http://is.gd/sCLOQz

February 19, 2012: The fastest-rotating pulsar known, PSR J1748-2446ad, spins faster than the blades in a kitchen blender!

February 20, 2012: Today is the 50th anniversary of the first American to orbit Earth. But not the first human. http://is.gd/1tOMMS

February 21, 2012: Satellites sometimes see solar eclipses too. is.gd/cU2rzM

February 22, 2012: From space, you can see a crescent Earth. And it’s as beautiful as you expect it to be. http://is.gd/qc0j7g

February 23, 2012: After galaxies collide, long streamers of gas can stretch between them like cosmic tentacles. http://is.gd/SgH5Cl

February 24, 2012: Space is big. I suspect that’s why they named it that. http://is.gd/r5Bboh #Seriously

February 25, 2012: Venus is bright enough to see during broad daylight. And today is a great chance to try! http://is.gd/ic6XcG

February 26, 2012: Sunspots are dark in visible light, but can be extremely bright in ultraviolet. http://is.gd/CiDluR

February 27, 2012: It’s very rare for an object in space to be a perfect sphere. But some things come close. http://is.gd/AW5eiL

February 28, 2012: The stars may seem fixed on the sky, but if you watch *very* carefully you’ll see their motion. is.gd/UVdSIM

February 29, 2012: The disk of the Milky Way is warped. In fact, many spiral galaxy disks are! is.gd/X70ahj

March 1, 2012: Much like humans, when stars are babies they blow gas out of both ends. is.gd/6zl9Y5

March 2, 2012: Venus is bright enough to cast shadows. So is Jupiter! is.gd/fDuayc

March 3, 2012: The rising Moon’s shape can be squished and massively distorted by Earth’s air. http://goo.gl/FGofa

March 4, 2012: Lightning storms have been spotted on Saturn… that last for nearly a year. http://is.gd/uYMcBe

March 5, 2012: Red dwarf stars are dim, cool, and dinky. But sometimes they erupt with HUGE flares. http://is.gd/mfBKGw

March 6, 2012: Most galaxies in the Universe live in clusters. The Coma Cluster has over 1000 galaxies! http://is.gd/JnLvSf

March 7, 2012: A solar explosion called a coronal mass ejection can blast out a billion tons of subatomic particles. http://is.gd/wqicKV

March 8, 2012: Ice crystals in the air can project a lovely ring around the Sun or Moon, called a halo. http://is.gd/gFW2AY

March 9, 2012: Some of the closest stars known are so faint they’re invisible to the naked eye. http://is.gd/dnmZ0D

March 10, 2012: Saturn doesn’t have one ring: it has *thousands*. http://is.gd/uAJ5c8

March 11, 2012: The structure of the Universe is foamy, and some galaxies sit on the edge of a void. http://is.gd/Nq3v81

March 12, 2012: Tonight, Venus & Jupiter are just 3 degrees apart at sunset. They’re the 3rd & 4th brightest natural nighttime objects.

March 13, 2012: Why does the Moon look so huge on the horizon? It’s an illusion! http://goo.gl/nYIMs

March 14, 2012: As the Earth orbits the Sun, the line dividing day and night – the terminator – changes its angle. http://is.gd/93tQS0

March 15, 2012: From Pluto, the Sun is fainter than it is from Earth, but still can be 450x brighter than the full Moon. goo.gl/7P24G

March 16, 2012: From Pluto, the Sun is so far away it would be a point in the sky like an incredibly bright star. http://t.co/fmBJzkmN

March 17, 2012: All the iron in your blood and all the calcium in your bones were created in exploding stars. http://goo.gl/bb3Hv

March 18, 2012: It took Apollo over 4 days to get from the Earth to the Moon. Their radio transmissions made it back in 1.3 seconds.

March 19, 2012: Tonight’s the spring equinox! Can you stand a broom on end? Yes, just like EVERY OTHER DAY. http://goo.gl/fmB7D

March 20, 2012: Jupiter’s moon Io is more geologically active than Earth. Volcanoes constantly erupt there! goo.gl/DoKSR

March 21, 2012: As stars orbit the galaxy, they can plow through interstellar dust and create huge shock waves. http://goo.gl/DkXCh

March 22, 2012: The Earth is hit by more cosmic debris than the Moon is, but erosion destroys the evidence here. http://goo.gl/lJOhD

March 23, 2012: Some galaxies are cannibals. They eat other galaxies and grow huge. http://goo.gl/R931

March 24, 2012: Not all telescopes are on the ground or in space. SOFIA is inside an airplane with a hole in the side! http://goo.gl/xiPy

March 25, 2012: The red supergiant Betelgeuse will explode someday, but it’s too far away to hurt us. http://goo.gl/hvil1

March 26, 2012: Betelegeuse will explode one day. Maybe tonight, or maybe a million years from now. http://goo.gl/UOc4

March 27, 2012: Betelgeuse isn’t the nearest star that can go supernova. That honor goes to Spica. http://goo.gl/d6UOA

March 28, 2012: If your eyes could see into the far-infared, Betelgeuse would look blue. http://goo.gl/5R18f

March 29, 2012: Our Sun has dark sunspots, but bright hot spots have been detected on Betelegeuse. http://goo.gl/yaBZZ

March 30, 2012: Betelgeuse will someday explode, but until then it’s blowing out a dense wind of gas. http://goo.gl/Uk2Ql

March 31, 2012: One of the constituents of the red supergiant Betelegeuse? Sand. http://goo.gl/ybZh1

April 1, 2012: Time travel is certainly impossible; otherwise my future self would stop me from tweeting thi

April 2, 2012: The Universe is expanding! And we know how fast: 74.2 ±3.6 km/sec/megaparsec. http://goo.gl/Se5xp

April 3, 2012: A different way of measuring the Universe’s expansion gets 73.8 +/-2.4 km/sec/megaparsec. http://goo.gl/OX298

April 4, 2012: Not only is the Universe expanding, the expansion is accelerating! http://goo.gl/nzqOM

April 5, 2012: A single exploding star can be so bright it can be seen across 13.14 billion light years! Maybe. http://goo.gl/uLJp2

April 6, 2012: The most distant object ever seen is a galaxy at an ego-crushing distance of 13.2 billion light years. http://goo.gl/NIJju

April 7, 2012: V445 Puppis is a binary system where the two stars will eventually coalesce and explode. http://goo.gl/xVBH9

April 8, 2012: The least massive stars in the Universe, red dwarfs, may have lifespans of a trillion years.

April 9, 2012: Other planets get hurricanes too. Jupiter’s are bigger than the Earth! http://goo.gl/hPgwq

April 10, 2012: If you miss the Transit of Venus on June 6, you won’t see another until December 2117. http://goo.gl/aMmYv

April 11, 2012: Neptune, like Earth, is blue. But Neptune’s color is from methane, which absorbs red light. http://goo.gl/dn7nc

April 12, 2012: Geysers on Enceladus blow out 250 kg of water per second. It’ll run out in 13 billion years. http://is.gd/Okra82

April 13, 2012: Sunspots grow and morph over time as the Sun’s magnetic field changes strength and shape. http://is.gd/ih2MYc

April 14, 2012: The Earth was formed when the Universe was almost exactly 2/3 its present age. We’ve been around for 4.56 billion years.

April 15, 2012: Tonight Saturn is at opposition: as close as it gets to Earth this year, and the best time to see it. http://goo.gl/bkGyR

April 16, 2012: All the planets in the solar system have moons except Mercury and Venus, the two closest to the Sun.

April 17, 2012: Space Shuttle Discovery flew 39 missions for a total of nearly 240 million kilometers. http://goo.gl/nNcjQ

April 18, 2012: Sunspots erupt in solar flares when tangled magnetic field lines explosively release their energy. Bang! http://is.gd/CiDluR

April 19, 2012: Some people say the Moon orbits the Sun more than it does Earth, but really, it’s *our* Moon. http://goo.gl/uRerf

April 20, 2012: Physicists use a unit of area called a barn, equal to 10^(-28) square meters, about the size of a uranium nucleus.

April 21, 2012: Jupiter’s moon Io was the first body other than Earth seen to have active volcanism. http://goo.gl/L9GMu

April 22, 2012:Pluto’s getting redder. http://goo.gl/QuKj4

April 23, 2012:Even Hubble can’t see the Apollo landers. They’re too small. http://goo.gl/J1sdl

April 24, 2012: Hubble Space Telescope once observed *the Sun*! http://goo.gl/bWCIM

April 25, 2012: Telescopes are referred to by their mirror/lens diameter, so Hubble is a 2.4 meter ‘scope – about 8 feet.

April 26, 2012: In 2008, a gamma-ray burst 7.5 billion light years away was visible to the naked eye! http://goo.gl/1mWlJ

April 27, 2012: The farthest object most people can see is the Andromeda Galaxy, about 2.5 million light years away. http://goo.gl/PA4Zv

April 28, 2012: Ripples in the fireball from the Big Bang are still visible. They tell us what it was like back then. http://goo.gl/koS8m

April 29, 2012: The oldest star ever found was born just 500 million years after the Universe itself! http://goo.gl/Ydja0

April 30, 2012: The debris flying out from titanic supernova explosions can be seen to expand even as we watch. http://goo.gl/09cjK

May 1, 2012: Ice crystals in the air can project a lovely ring around the Sun or Moon, called a halo. http://is.gd/gFW2AY

May 2, 2012: In 2011, a spacecraft orbiting Mars watched a Martian moon partially eclipse Jupiter! http://goo.gl/0Tl0G

May 3, 2012: In 2008, a spacecraft orbiting Mars took a picture of home. goo.gl/Wu0J6

May 4, 2012: The biggest galaxies in the Universe have over a *trillion* stars! http://goo.gl/dH4uk

May 5, 2012: How far from your eye must you hold a dime to match the Moon’s size? Guess again: it’s 6 feet! http://goo.gl/JFVZW

May 6, 2012: Material at the center of the Sun is so compressed that it’s 150 times denser than water. http://is.gd/3K5Kv7

May 7, 2012: In interstellar space, on average there’s just one particle per cc (a bit smaller than a six-sided die).

May 8, 2012: An easy way to remember the number of seconds in a year: pi x 10 million. Accurate to better than 0.5%.

May 9, 2012: When galaxies collide, their mutual gravity can draw out long tendrils of gas from each other. http://goo.gl/jaItO

May 10, 2012: An asteroid hitting Mercury releases 60% more energy than it would on Earth. Why? Speed. http://goo.gl/xUUw7

May 11, 2012: Sunspots are where the Sun’s magnetic field won’t let cool gas sink, like a clogged drain. http://is.gd/ih2MYc

May 12, 2012: If you lived on Pluto, the United States wouldn’t even be one year old.

May 13, 2012: A supernova has to be less than about 75 light years away to hurt us. No star that close can explode, so we’re OK.

May 14, 2012: The nearest star that can go supernova is Spica – it’s 260 light years away, so we’re safe. http://goo.gl/d6UOA [NOTE: this is not quite correct. Please see BAFact for May 18, 2012.]

May 15, 2012: The Sun cannot go supernova. A single star needs to be about 8x the mass of the Sun to explode. http://goo.gl/GAK22

May 16, 2012: Low mass stars *can* go supernova… but they need the help of a companion. http://goo.gl/WJl1x

May 17, 2012: Merging white dwarfs can form a neutron star, triggering a supernova. http://goo.gl/hs17n

May 18, 2012: The nearest star(s) to Earth that can go supernova is(are) IK Peg, at 150 light years away! http://goo.gl/QZECx

May 18, 2012 [Part 2] (correction of earlier BAFact from May 14, 2012): The nearest massive star that can go supernova is Spica – it’s 260 light years away, so we’re safe. http://goo.gl/d6UOA

May 19, 2012: An exploding star can fling away its octillion-ton core 100s of times faster than a rifle bullet! http://goo.gl/96sk

May 20, 2012: Sunspots look small, but only because the Sun is huge. Many are far larger than the entire Earth! http://is.gd/X2cSyI

May 21, 2012: The coolest brown dwarf found is actually about room temperature! http://goo.gl/yL3Eg

May 22, 2012: The first exoplanets discovered were found in 1992, circling the ultradense cinder of a supernova. http://goo.gl/C6n9c

May 23, 2012: The 1st confirmed planet found around a Sun-like star was 51 Peg b in 1995. Now we know of >700! http://goo.gl/Y5TRf

May 24, 2012: There may be hundreds of billions of planets in our galaxy alone! http://goo.gl/8BLrJ