What Is That in the Sky?

The short version, for the most common sightings: a dazzling, steady point low in the west after sunset, or low in the east before dawn, is almost always the planet Venus. A bright, steady point higher up in the evening is usually Jupiter. A steady reddish point is Mars or one of the red stars Antares, Betelgeuse and Aldebaran. A light that drifts silently across the sky in a minute or two is a satellite or the International Space Station; one that blinks or shows colored lights is an aircraft. A point that streaked and vanished within a second was a meteor.

The usual suspects

A handful of objects account for the great majority of "what was that?" sightings. Knowing their habits makes the answer obvious more often than not.

• Venus is the brightest thing in the sky after the Sun and Moon, bright enough to cast a faint shadow and to be mistaken for a landing aircraft. It never strays far from the Sun, so it appears only in the west after sunset or the east before sunrise, low down, as the "evening star" or "morning star." It shines with a steady white light.
• Jupiter is the next brightest and, unlike Venus, can ride high across the whole night, climbing well up in the south. Also steady and white.
• Mars is unmistakably orange when it is well placed, and its brightness varies enormously from one year to the next as its distance changes. It keeps to the ecliptic and does not twinkle.
• Saturn is a modest yellowish point, easy to overlook next to the brighter planets, again holding to the ecliptic.
• The bright stars. Sirius, blue-white and low in the south on winter evenings, twinkles so fiercely that people report it changing color and flashing. Arcturus and Capella are golden; Betelgeuse, Antares and Aldebaran are orange-red; Vega, Rigel and Spica are blue-white. Polaris, the North Star, is only moderately bright and sits almost due north at a height equal to your latitude.
• The International Space Station and satellites move, steadily and silently, which no star or planet does.

Two safe rules cover most cases. First, planets shine steadily and stars twinkle. Second, a light that moves is a satellite, a plane or a meteor, never a star or planet. Everything else the tool sorts out by working the geometry for your exact place and time.

Frequently asked questions

How can I tell a planet from a star?

Planets shine with a steady light while stars twinkle. A star is so far away it is a true point of light, so turbulence in the air breaks it up into a flicker; a planet shows a tiny disc that averages the turbulence out and holds steady. Planets also keep to a narrow band across the sky, the ecliptic, the same path the Sun and Moon follow. Twinkling is strongest low near the horizon, where you look through the most air, so even a planet can shimmer a little there.

What is the very bright star in the west after sunset?

Almost always the planet Venus, the brightest point of light in the sky after the Sun and Moon. Because Venus orbits closer to the Sun than Earth does, it only ever appears low in the west after sunset or low in the east before sunrise, and is never seen near midnight. A bright, steady point higher up or in the south or east on an evening is more often the planet Jupiter.

I saw a bright reddish star. What was it?

The usual reddish culprits are the planet Mars and three orange-red stars: Antares in Scorpius, Betelgeuse in Orion, and Aldebaran in Taurus. Mars shifts position from month to month and shines steadily; the stars hold fixed places and twinkle. Enter the direction, height and time above and this tool will tell you which of them was actually in that part of your sky.

I saw a light moving slowly across the sky with no sound or blinking. What was it?

Most likely a satellite or the International Space Station catching sunlight. They look like steady stars that glide from one side of the sky toward the other over a minute or two, then often fade out as they cross into the shadow of Earth. They are seen mainly in the couple of hours after dusk and the couple before dawn, when the ground is dark but they are still lit. For the exact passes over your location, use a pass predictor such as heavens-above.com.

It blinked or flashed in different colors. Was it something unusual?

A light that blinks, especially in red, green or white, is almost certainly an aircraft; planes carry blinking navigation lights and a white strobe. This tool deals in positional astronomy, the Sun, Moon, planets, stars and satellites, not in unidentified objects. The simple rule is that a steadily moving, non-blinking light is a satellite, while a blinking one, or one showing more than one color, is a plane.

Can it identify something I saw on an earlier night?

Yes. Enter the date and the rough time you saw it along with the direction and height, and the tool recomputes the whole sky for that past moment. That is the one thing a point-your-phone star app cannot do, because it only shows the sky as it is right now, not as it was when you were actually looking.

Why does it need my location and the time?

Because the same star or planet sits in a completely different direction and height depending on where you stand and when you look. One object can be low in the east at one hour and high in the south a few hours later, and two observers far apart see it in different parts of their skies at the same instant. Without a place and a time there is no way to say what was where you were looking.

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