Welcome to the Boston Astronomy website ...

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This website has been created by and is supported by a group of Boston, MA - area amateur astronomers. It is intended to be a convenient site to access news and information about astronomy and space-related activities of interest to the community and the public.

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Factor (s)	Multiple	Symbol	Definition	Comparative examples & common units	Orders of magnitude
10−44	1 Planck time.	tP	The time required to travel one Planck length at the speed of light (c)	5.4×10−20 ys = 5.4×10−44 s: One Planck time tP = ≈ 5.4×10−44 s[2] is the briefest physically meaningful span of time. It is the unit of time in the natural units system known as Planck units.	10−20 ys, 10−19 ys (10−44 s, 10−43 s)
10−24	1 yoctosecond	ys[3]	Yoctosecond, (yocto- + second), is one septillionth of a second	0.3 ys: mean life of the W and Z bosons.[4][5][a] 0.5 ys: time for top quark decay, according to the Standard Model. 1 ys: time taken for a quark to emit a gluon. 23 ys: half-life of 7H.	1 ys and less, 10 ys, 100 ys
10−21	1 zeptosecond	zs	Zeptosecond, (zepto- + second), is one sextillionth of one second	7 zs: half-life of helium-9's outer neutron in the second nuclear halo. 17 zs: approximate period of electromagnetic radiation at the boundary between gamma rays and X-rays. 300 zs: approximate typical cycle time of X-rays, on the boundary between hard and soft X-rays. 500 zs: current resolution of tools used to measure speed of chemical bonding[6]	1 zs, 10 zs, 100 zs
10−18	1 attosecond	as	One quintillionth of one second	12 attoseconds: shortest measured period of time.[7]	1 as, 10 as, 100 as
10−15	1 femtosecond	fs	One quadrillionth of one second	1 fs: Cycle time for 390 nanometre light; transition from visible light to ultraviolet; light travels 0.3 micrometers (µm)	1 fs, 10 fs, 100 fs
10−12	1 picosecond	ps	One trillionth of one second	1 ps: half-life of a bottom quark; light travels 0.3 millimeters (mm) 4 ps: Time to execute one machine cycle by an IBM Silicon-Germanium transistor	1 ps, 10 ps, 100 ps
10−9	1 nanosecond	ns	One billionth of one second	1 ns: Time to execute one machine cycle by a 1 GHz microprocessor 1 ns: Light travels 30 centimetres (12 in)	1 ns, 10 ns, 100 ns
10−6	1 microsecond	µs	One millionth of one second	1 µs: Time to execute one machine cycle by an Intel 80186 microprocessor 4–16 µs: Time to execute one machine cycle by a 1960s minicomputer	1 µs, 10 µs, 100 µs
10−3	1 millisecond	ms	One thousandth of one second	1 ms: time for a neuron in human brain to fire one impulse and return to rest[8] 4–8 ms: typical seek time for a computer hard disk 100–400 ms (=0.1–0.4 s): Blink of an eye[9] 18–300 ms (=0.02–0.3 s): Human reflex response to visual stimuli	1 ms, 10 ms, 100 ms
100	1 second	s		1 s: 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.[10] 60 s: 1 minute	1 s, 10 s, 100 s
103	1 kilosecond (16.7 minutes)	ks	One thousand seconds	3.6 ks: 3600 s or 1 hour 86.4 ks: 86 400 s or 1 day 604.8 ks: 1 week	103 s, 104 s, 105 s
106	1 megasecond (11.6 days)	Ms	One million seconds	2.6 Ms: approximately 1 month 31.6 Ms: approximately 1 year ≈ 107.50 s	106 s, 107 s, 108 s
109	1 gigasecond (32 years)	Gs	One billion seconds	2.1 Gs: average human life expectancy at birth (2011 estimate)[11] 3.16 Gs: approximately 1 century 31.6 Gs: approximately 1 millennium	109 s, 1010 s, 1011 s
1012	1 terasecond (32 000 years)	Ts	One trillion seconds	6 Ts: time since the appearance of Homo sapiens (approximately)	1012 s, 1013 s, 1014 s
1015	1 petasecond (32 million years)	Ps	One quadrillion seconds	7.1–7.9 Ps: 1 galactic year (225-250 million years)[12] 143 Ps: the age of the Earth[13][14][15] 144 Ps: the approximate age of the Solar system[16] and the Sun.[17] 430 Ps: the approximate age of the Universe 440 Ps: the half-life of thorium 232	1015 s, 1016 s, 1017 s
1018	1 exasecond (32 billion years)	Es	One quintillion seconds	312 Es: Estimated lifespan of a 0.1 solar mass red dwarf star.	1018 s, 1019 s, 1020 s
1021	1 zettasecond (32 trillion years)	Zs	One sextillion seconds	3 Zs: Estimated duration of Stelliferous Era. 9.8 Zs: the lifetime of Brahma in Hindu mythology	1021 s, 1022 s, 1023 s
1024	1 yottasecond (32 quadrillion years)	Ys	One septillion seconds	1.6416 Ys: Estimated half-life of the meta-stable 20983Bi radioactive isotope. 6.616×1050 Ys: Time required for a 1 solar mass black hole to evaporate completely due to Hawking radiation, if nothing more falls in.	1024 s, 1025 s, 1026 s and more

Factor (a)	Multiple	Common units	Orders of magnitude
10−50		Planck time, the shortest physically meaningful interval of time ≈ 1.71×10−50 a	10−50 a
10−24	1 yoctoannum	—	1 ya and less, 10 ya, 100 ya
10−21	1 zeptoannum	—	1 za, 10 za, 100 za
10−18	1 attoannum	—	1 aa, 10 aa, 100 aa
10−15	1 femtoannum	—	1 fa, 10 fa, 100 fa
10−12	1 picoannum	—	1 pa, 10 pa, 100 pa
10−9	1 nanoannum	1 second = 3.17 × 10−8 a ≈ 10-7.50 a	1 na, 10 na, 100 na
10−6	1 microannum	1 minute = 1.90 × 10−6 a 1 hour = 1.40 × 10−4 a	1 ua, 10 ua, 100 ua
10−3	1 milliannum	1 day = 2.73 × 10−3 a 1 week = 1.91 × 10−2 a	1 ma, 10 ma, 100 ma
100	1 annum	1 average year = 1 annum (= 365.24219 SI days) 1 decade = 10 a 1 century = 100 a	1 a, 10 a, 100 a
103	1 kiloannum	millennium = 1000 a	103 a, 104 a, 105 a
106	1 megaannum	epoch = 1,000,000 a	106 a, 107 a, 108 a
109	1 gigaannum	aeon = 1,000,000,000 a 13.8 Ga = 1.38×1010 a ≈ 13.8 billion years, the approximate age of the Universe	109 a, 1010 a, 1011 a
1012	1 teraannum	—	1012 a, 1013 a, 1014 a
1015	1 petaannum	—	1015 a, 1016 a, 1017 a
1018	1 exaannum	19 exaannum, the estimated half-life of the "stable" 20983Bi radioactive isotope	1018 a, 1019 a, 1020 a
1021	1 zettaannum	—	1021 a, 1022 a, 1023 a
1024	1 yottaannum	—	1024 a, 1025 a, 1026 and more