Venus orbits inside Earth’s orbit, so the sunlit half does not stay turned the way it does for Mars. From here the planet runs through phases — crescent, half, gibbous, and back — for a geometric reason that is not the Moon’s. Inferior conjunction puts Venus between Earth and the Sun, near “new,” and usually lost in the glare. Superior conjunction puts it on the far side, near “full,” and still near the Sun in the sky. The long evening and morning stretches are the greatest elongations, when Venus stands farthest in angle from the Sun. Pair it with the solar map (where Venus sits among the planets), with Moon phases (the same words, a moon going around us), with retrograde (Earth passing an outer planet, not this inner one), with seasons (Earth’s axis, not this angle), and with gravity, the pull that keeps both worlds on their tracks.
Educational schematic — circular orbits, flattened onto one plane, disks exaggerated so a phone can see them. The viewpoint holds Earth on the right so the phase is easy to read. Both worlds still orbit the same way. Circle radii use the semimajor-axis ratio on NASA’s Venus Fact Sheet, 0.723. That sheet lists Venus’s eccentricity as 0.0068 and its orbit inclination as 3.395°, so a real inferior conjunction is usually a thin crescent in the glare, not a transit across the Sun. This coplanar cartoon goes dark at the lineup. Not an ephemeris. Not a date. Not for pointing a telescope from Campbell or anywhere else, and not a reason to look at the Sun.
Interactive · Top-down
North up · Earth held on the right · Venus walks counterclockwise
As seen from Earth · bright limb faces the Sun · ghost ring is the largest size on these circles
Sun
Venus · inner, faster
Earth · viewpoint held
Line of sight
+513 d
Literacy · words for the phase
Inferior planet
NASA’s Basics of Space Flight: Mercury and Venus are inferior planets because their orbits are closer to the Sun than Earth’s, not because they matter less. They always appear near the Sun in the morning or evening sky. Mars, on the retrograde desk, is a superior planet. Its orbit is outside ours, so it does not run through this crescent-to-full range.
Phase
The sunlit fraction we see. The same chapter: an inferior planet can show nearly the whole range, from the dark “new” phase, to a slim crescent, to a mostly lit gibbous, approximating full on the far side of the Sun. A NASA Hubble caption says the same thing in one line — because Venus is closer to the Sun than Earth, it appears to go through phases, like the Moon. The Moon’s phases are a body going around us. These are a body going around the Sun inside our own orbit.
Inferior conjunction
Venus approximately between Earth and the Sun, the three nearly in a line. Basics of Space Flight uses that definition, and adds that an exact crossing of the Sun’s face is a transit. A 1977 NASA Facts pamphlet says this is also when Venus comes closest to Earth, then becomes a morning star. The fact sheet’s 3.395° inclination is why the usual case is a thin crescent in the glare. This slider’s zero is a schematic lineup, not a transit date.
Superior conjunction
Earth and Venus on opposite sides of the Sun, again nearly in a line. That is the far-side lineup. The phase is near full, the disk on these circles is as small as it gets, and Venus is still close to the Sun in the sky. NASA’s Earth Observatory describes the circuit as evening star, then lost near the Sun, then morning star, then passing behind the Sun — about 19 months in their wording. The day count on this slider is the fact sheet’s 583.92-day synodic period, not a conversion I invented from “19 months.”
Elongation
The apparent angle from the Sun, in NASA’s space-flight chapter. The 1977 pamphlet splits it east and west: eastern elongation is the evening sky, after sunset; western elongation is the morning sky, before sunrise. A NASA skywatching page says Venus is visible for only a couple of months at a time around its greatest separation from the Sun, which that page calls elongation. Greatest eastern and greatest western on this desk are the tangent points of these circles — schematic positions, not an almanac.
Synodic period
The repeat of the same Sun–Earth–Venus alignment. The Venus Fact Sheet lists it as 583.92 days. Sidereal orbit periods on that sheet are 224.701 days for Venus and 365.256 days for Earth. The slider can walk one of those synodic laps. It does not name the next evening star over Campbell.
Crescent and distance
Closer on the inner orbit means a larger disk and a thinner crescent. Farther, toward superior conjunction, means a smaller disk and a fuller phase. APOD (21 May 2020) follows Venus as an evening star: it grows larger because it is approaching Earth, and the crescent narrows as it swings toward our line of sight to the Sun. The February 2025 notes add the brightness twist, without a magnitude this page will copy. The ghost ring on the lower panel is the largest size these circles allow. It is not a published arcsecond.
Sources · public NASA education
Cited, not invented
NASA NSSDCA — Venus Fact Sheet — semimajor-axis ratio 0.723; sidereal orbit periods 224.701 days (Venus) and 365.256 days (Earth); synodic period 583.92 days; mean orbital velocity 35.02 km/s (Venus) and 29.78 km/s (Earth); eccentricity 0.0068; inclination 3.395°. Those means set the circles. They are not a nightly position. The sheet’s V(1,0) magnitude is a normalized brightness, not an apparent magnitude for this slider, so it is not used.
NASA Science — Basics of Space Flight, Chapter 1 — inferior planets orbit closer to the Sun than Earth and stay near the Sun in the morning or evening sky; elongation is their apparent angle from the Sun; they show phases from dark “new,” through crescent, to gibbous, approximating full on the far side; inferior conjunction is the planet approximately between Earth and Sun (a transit if it crosses the Sun’s face); superior conjunction puts Earth and the planet on opposite sides of the Sun.
Astronomy Picture of the Day — Phases of Venus (2020 May 21) — Venus’s sunlit hemisphere waxes and wanes like the Moon; in that evening-star sequence the disk grows larger as Venus approaches Earth and the crescent narrows toward the Sun; inferior conjunction follows, then Venus becomes a morning star. The dates and the half-degree offset on that page belong to 2020, not this slider.
NASA Science — What’s Up: February 2025 — through a telescope Venus becomes larger as it comes closer, and becomes a slimmer crescent; unlike the Moon, it is not brightest when full; the full phase is the far side of the Sun, and the closer crescent looks much larger. The February and March dates on that page are that season.
NASA Science — Venus cloud tops (Hubble, 1995) — because Venus is closer to the Sun than Earth, it appears to go through phases like the Moon; when it swings close, the disk grows and changes from a full disk to a crescent. The miles and kilometers in that caption are the distance of that exposure, not a distance this slider prints.
NASA Science — Planetary alignments and planet parades — Venus is visible for only a couple of months at a time around its greatest separation from the Sun (that page calls the separation elongation), just after sunset or before sunrise.
NASA Earth Observatory — Viewing Venus from the Space Station — evening star for a few months, then lost near the Sun, then morning star, then behind the Sun, a circuit that page calls 19 months. This slider counts the fact sheet’s 583.92 days instead of turning “19 months” into a new figure.
NASA Facts NF-86, The Planet Venus (1977), via NTRS — eastern elongation is the evening sky; western elongation is the morning sky; Venus moves from superior conjunction east of the Sun as an evening star, through inferior conjunction, and then becomes a morning star; greatest elongation is marked on that orbit diagram. The pamphlet’s rounded period and surface temperature are not the numbers used here.
Classroom picture of an inner orbit and the phase it shows from Earth. Not an ephemeris, not a pointing aid, and not a Campbell observing plan. Days on the slider are a coordinate of these circles, counted from a schematic inferior conjunction. The angle is the Sun–Venus–Earth angle on the cartoon. Periods, the 0.723 ratio, and the inclination are the ones NASA publishes on the pages above. Earthrise preview: NASA / Bill Anders (public domain).