5 Seconds of Summer is an Australian pop rock band. Formed in Sydney in 2011, the band consists of Luke Hemmings (vocals, guitar), Michael Clifford (guitar, vocals), Calum Hood (bass guitar, vocals) and Ashton Irwin (drums, vocals).

5 Seconds of Summer began in 2011 when Luke Hemmings, Michael Clifford and Calum Hood, who all attend the same school, joined together and started posting videos of themselves performing covers of popular songs to YouTube. Their cover of the Chris Brown and Justin Bieber hit "Next to You" received over 200,000 hits. They have since amassed over 4 million YouTube views, and a large following on social media sites Twitter and Facebook. In December 2011, they were joined by drummer Ashton Irwin, and the current 5 Seconds of Summer lineup came to be. The band attracted some keen interest from major music labels and publishers, and have signed a publishing deal with Sony ATV Music Publishing. Despite having had no promotion apart from on Facebook and Twitter, their first music release, an EP entitled Unplugged, reached number 3 on the iTunes chart in Australia, and Top 20 in both New Zealand and Sweden.^{[citation needed]}

The second (SI unit symbol: s) is the International System of Units (SI) base unit of time and also a unit of time in other systems (abbreviated s or sec). Between 1000 (when al-Biruni used seconds) and 1960 the second was defined as 1/86,400 of a mean solar day (that definition still applies in some astronomical and legal contexts). Between 1960 and 1967, it was defined in terms of the period of the Earth's orbit around the Sun in 1900, but it is now defined more precisely in atomic terms. Seconds may be measured using mechanical, electric or atomic clocks.

However, 19th- and 20th-century astronomical observations revealed that this average time is lengthening and thus the sun–earth motion is no longer considered a suitable basis for definition. With the advent of atomic clocks, it became feasible to define the second based on fundamental properties of nature. Since 1967, the second has been defined to be:

SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g., the millisecond (one thousandth of a second), the microsecond (one millionth of a second), and the nanosecond (one billionth of a second). Though SI prefixes may also be used to form multiples of the second such as kilosecond (one thousand seconds), such units are rarely used in practice. The more common larger non-SI units of time are not formed by powers of ten; instead, the second is multiplied by 60 to form a minute, which is multiplied by 60 to form an hour, which is multiplied by 24 to form a day.

Summer (/ˈsʌmər/ SU-mər) is the warmest of the four temperate seasons, between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, with day-length decreasing as the season progresses after the solstice. The date of the beginning of summer varies according to climate, culture, and tradition, but when it is summer in the Northern Hemisphere it is winter in the Southern Hemisphere, and vice versa.

From an astronomical view, the equinoxes and solstices would be the middle of the respective seasons, but a variable seasonal lag means that the meteorological start of the season, which is based on average temperature patterns, occurs several weeks later than the start of the astronomical season. According to meteorologists, summer extends for the whole months of June, July, and August in the northern hemisphere and the whole months of December, January, and February in the southern hemisphere. Under meteorological definitions, all seasons are arbitrarily set to start at the beginning of a calendar month and end at the end of a month. This meteorological definition of summer also aligns with the commonly viewed notion of summer as the season with the longest (and warmest) days of the year (365 days), in which daylight predominates. The meteorological reckoning of seasons is used in Austria, Denmark and the former USSR; it is also used by many in the United Kingdom, where summer is thought of as extending from mid-May to mid-August. In Ireland, the summer months according to the national meteorological service, Met Éireann, are June, July and August. However, according to the Irish Calendar summer begins 1 May and ends 1 August. School textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June.