A Comet’s Tail Always Points Away from the Sun
Contrary to what you might think, a comet’s tail doesn’t trail behind it like a rocket plume. Comets have a coma, the cloud around the nucleus, that may extend hundreds of thousands of kilometers. They also have two tails, a dust tail and a gas tail, and the pressure of sunlight and the solar wind blow the dust and gas away from the Sun, regardless of the comet’s direction. This means that as a comet travels away from the Sun, its tail actually precedes it, like a spotlight leading the way through the darkness of space.
2 tails
Tails of a typical comet, both pointing away from the Sun
Previous 7 days
- Apr 18 Dwarf Planets & Small BodiesHalley’s Comet Will Return in 2061
- Apr 17 Dwarf Planets & Small BodiesComets Might Have Brought Water to Earth
- Apr 16 Dwarf Planets & Small BodiesComets Can Have Two Tails (or More)
- Apr 15 Night SkyThe Faint Unicorn Constellation Dates to 1612
- Apr 14 Night SkyThe Stars in a Constellation Aren’t Actually Close to Each Other
- Apr 13 PlanetsNeptune’s Atmosphere Cooled Then Warmed for Unknown Reasons
- Apr 12 PlanetsUranus Rolls Around the Sun on Its Side
Today’s astronomy fact of the day
A new astronomy fact appears on this page every day at midnight. Each one states a single finding, gives the number behind it and explains why it is true. Every fact links to the source it came from, such as NASA, ESA, JPL or a mission page, so you can read the original.
The card above shows the key number for the day and counts up to it. Read the fact, check the figure, then open the source link to see the claim in context. The fact for a given date stays the same after it is published.
What kinds of space facts you get
Facts fall into three groups, so the daily space fact is not always a trivia item.
- Space history anniversaries. Events that happened on the same date in a past year, such as the first photo of Earth from space on October 24, 1946, or the Venera 9 landing on Venus on October 22, 1975.
- Tonight’s sky. Meteor shower peaks, full moons and other events you can see on or near that date, with the time and direction to look.
- Surprising evergreen facts. Saturn is less dense than water. The Sun holds 99.8% of the solar system’s mass. A galactic year lasts about 230 million years. These cover the Moon, the planets, stars, galaxies, black holes and the universe as a whole.
Topics rotate. A week of facts might include a moon, a mission, a black hole and an astronaut.
Space fact of the day for kids
Each fact runs about 80 to 140 words in plain language. A term such as thrust fault or Lagrange point gets a short explanation in the same sentence. Students in grade 3 and up can read the facts alone, and younger children can have them read aloud. The facts cover science and history only.
For a longer list, use the kid-friendly fact pages: moon facts for kids, planet facts for kids, solar system facts for kids, comet facts for kids and meteor facts for kids.
Use the daily space fact in the classroom
A fact that takes two minutes to read fits at the start of a lesson. Teachers use it in three ways.
- Bell-ringer. Put the title on the board before the lesson. Students write a one-sentence guess about why it is true, then read the fact and compare.
- Morning meeting. One student reads the fact aloud and the class finds the key number. Ask what the number would be if the object were twice as far away or twice as heavy.
- Source reading. Open the source link and find the sentence that supports the number. This practices the habit of checking where a claim comes from.
The key numbers also work as quick math. The Orionid meteor speed of 66 kilometers per second converts to miles per second. Saturn’s density of 687 kilograms per cubic meter compares to water’s 1,000. History facts give dates to subtract: the first crew reached the International Space Station in 2000, so count the years since.
The monthly meteor shower guide pairs well with the sky-event facts when a class wants to observe at home.
Browse astronomy facts by topic
These pages go deeper on the subjects the daily facts touch most often.
- Facts about Mars for the planet with the largest volcano and the biggest dust storms.
- Andromeda Galaxy facts for the nearest large galaxy.
- Types of black holes for the densest objects in the universe.
- Space records for the biggest, fastest and farthest.
- Famous astronauts for the people who flew the missions.
- Astronomy for beginners to start from the basics.
- The full facts archive for earlier facts.
Frequently asked questions
What is the space fact of the day?
It is one verified astronomy fact published on this page every day. Each fact gives the key number, explains why it is true and links to the source it came from, such as NASA, ESA or a mission page. Today’s fact is in the card at the top of the page.
Where can I get a daily space fact?
Right here. A new fact appears at midnight every day, and you can bookmark this page to see it each morning. NASA’s Astronomy Picture of the Day is a second daily source, and it pairs one image with a short explanation.
Are these facts suitable for kids?
Yes. Each fact is written in plain language, and any technical term is explained in the same sentence. Students in grade 3 and up can read them alone, and younger children can have them read aloud. The facts are about science and history only, with nothing graphic or frightening.
How often does the astronomy fact of the day change?
Every day at midnight. The fact for a given date does not change after it is published, so a link or a classroom schedule that points to a date always shows the same fact.
Where do the facts come from?
Each fact cites a primary source such as NASA, JPL, ESA, NOAA, the Smithsonian, a mission page or a published journal article. The key number in the card is checked against the cited page, and the source link sits under the fact.
What is a fun fact about space?
Saturn is less dense than water. Its average density is 687 kilograms per cubic meter, and water’s is 1,000, so Saturn would float in a bathtub large enough to hold it. The planet is mostly hydrogen and helium, the two lightest elements.