It isn't just the near (well, seemingly near) conversion of Venus and Jupiter, but Tuesday, June 30th will also be one second longer than any normal day. Tuesday will have what scientists call a 'leap second' which is made up of the fractions of seconds gradually adding up to an extra second, thus a 'leap second.'
Computers cannot keep up with leap seconds, as they are generally only decided upon mere months in advance. It is because of this that many think we should get rid of leap seconds entirely.
Confused? Me too, let's see how the today's best (and widely only) known astrophysicist Neil deGrasse Tyson and NASA explain it.
NASA explains tomorrow's extra second:
Or, if you prefer Neil's soothing voice (or words): https://twitter.com/neiltyson/status/615266604100796416 https://twitter.com/neiltyson/status/615266915842396160 https://twitter.com/neiltyson/status/615267522829545472 https://twitter.com/neiltyson/status/615269674574610432 https://twitter.com/neiltyson/status/615269855835631616
The difference of 2 milliseconds, or two thousandths of a second — far less than the blink of an eye — hardly seems noticeable at first. But if this small discrepancy were repeated every day for an entire year, it would add up to almost a second. In reality, that’s not quite what happens…
The length of day is influenced by many factors, mainly the atmosphere over periods less than a year. Our seasonal and daily weather variations can affect the length of day by a few milliseconds over a year. Other contributors to this variation include dynamics of the Earth’s inner core (over long time periods), variations in the atmosphere and oceans, groundwater, and ice storage (over time periods of months to decades), and oceanic and atmospheric tides.
I, myself, prefer Neil's lovely voice, so here's to that glass of champagne!