So, in summation of the ideas in this thread, it should be one of these:
1) Atmospheric lightning
2) Venus - It won't change in brightness much on a clear night.
3) Drone - Usually not all that bright, though perhaps police units are.
4) Earthquake lightning -- An earthquake should be expected, I presume.
5) Iridium flare -- these orbiting satellites move briskly.
6) Supernova -- but how about a nova, instead. Supernova are long-lasting.
7) Flare
8) Meteor traveling almost directly toward the observer. [I'm guessing some hint of color should be seen, but I could be wrong.]
9) Aircraft landing lights on approach before turning in-line with the runway.
10) ISS reflection into a peculiar atmospheric condition.
11) Eye problem.
12) Helicopter. Police helicopters have bright lights. [They won't be that high in the sky if you can't hear them, or are they super quiet these days?]
13) Ball lightning.
14) St. Elmo's fire.
15) Fuel dump of a rocket.
16) Aircraft fuselage reflection with some atmospheric effects.
17) UFO
18) My old neighbor doing his in-the-sky light fun, which I've witnessed.
An impressive array of answers, IMO.
Did I miss any?
The 60 deg. altitude will knockout some of these. [At 60 deg., a "quiet" helicopter would be about 4,500 ft. high at only 1/2 mile away, and too high for a search light.] The, apparent, lack of sound culs the list a little more, perhaps.
The more details one can take note of immediately, and write them down, then the far greater chance one of these, or more is the answer.
I added #18 because some folks just have fun spoofing others, including my old neighbor back in the early 60s when the radio DJs would report any UFO sightings. [My neighbor quit doing these things after he burnt-down 1/2 of his other neighbor's large ash tree.
]