# How fast does Venus move as seen from the earth?

So last night I was about to sleep with the window in front of me. there was a 3 inch gap between the curtains that let me see a small portion of the sky. I could see something magnificently bright in the sky that couldn't be anything but Venus. So while I was looking at it for about 1-2 minutes it gradually moved out of my sight. That seemed pretty fast. I mean I kinda estimated that with such a speed it could move from east to west in less than 2 hours. So is that normal?

• Ganbustin.Good answer no more to be said really with my grand children we talk of 1degree = 4minutes and demonstrated transit of the moon(1/2 deg) took 2minutes Commented Jan 14, 2015 at 9:58
• I just found this thread - I saw the EXACT same thing one week ago. Venus was shining so bright that my boyfriend told me to come to the window to look at it. We got our binoculars out and used an app to determine that it was Venus. About 20 minutes later my boyfriend went to another room in the apartment and I was sitting on the couch, still looking out the window at Venus, when suddenly it started moving. Rapidly. First I thought my eyes were playing tricks on me but it kept moving until it was out of my line of vision completely. I called my boyfriend and said "come here, it moved. it's gon
– Lex
Commented Jan 4, 2017 at 22:30
• e!" He didn't believe me until he came and looked and saw it was nowhere to be found. So bizarre.
– Lex
Commented Jan 4, 2017 at 22:30
• Well, once I got tricked by an airplane thinking it was a moving star. lol! But if your app says it's Venus, it probably is, or maybe you were witnessing International Space Station? Are you sure it was not a cloudy night? And perhaps the shiny object was camouflaged by a big cloud? Happens to me a lot. Commented Jan 6, 2017 at 7:46

The Earth rotates on its axis once every 24 hours. (Well, actually a little less, by about 17 minutes, but close enough.) That's $360^\circ$ in 24 hours, or about $15^\circ$ per hour. $15^\circ$ is 30 times the width of the Sun or Moon. The Sun moves exactly that fast (on average), the stars a smidgen faster, and the Moon a tad slower. (The Moon lags behind the stars by approximately its own width every hour.)

Since Venus is never more than about $45^\circ$ from the Sun, it always sets at most 3 hours after the Sun does, and rises at most 3 hours before.

• So, according to this fact, what I actually saw was merely Venus, cause it was around midnight. Is it possible for a satellite to be that shiny? Commented Jan 14, 2015 at 11:32
• @ye9ane Since 2009, the International Space Station is now the second brightest object in the night sky, even outshining Venus. Perhaps that is what you saw? Commented Jan 14, 2015 at 15:24
• I looked up NASA to spot the station from my location. It can't be it, since it said on that particular night it was not visible at all. Commented Jan 14, 2015 at 19:02
• @ye9ane I assume you meant "clearly not Venus". Jupiter is currently bright enough to be easily mistaken for Venus, and is high in the sky at midnight. Or it could have been Sirius, not as bright as Venus or Jupiter, but plenty bright enough to stand out. All of these move at roughly the same 15 degrees per hour. It would not have been the space station. ISS really books, completely passing from horizon to horizon in at most a minute. It cannot be mistaken for a non-satellite. Commented Jan 15, 2015 at 9:38
• Did you mean to say "a little less, by about 4 minutes" instead of 17?
– user21
Commented Aug 8, 2015 at 2:20

This was likely the international space station. It can take up to 5 minutes for the ISS to pass from horizon to horizon. However, later in the night, that time gets shorter as the suns relative angle to the ISS and you changes. It will be quickly back into the shadow of the earth and lower on the horizon, staying low throughout. It can reach up to -8 magnitude on occasion. This is very easy to see, however near midnight it would likely be closer to 0 or 1.