John Gizis

Professor, Physics and Astronomy University of Delaware

  • Newark DE

Prof. Gizis focuses his research on improving the understanding of stars and brown dwarfs (failed stars).

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3 min

The science of leap day

The arrival of a leap year brings with it myths, legends and superstitions about its origin. John Gizis, professor of physics and astronomy at the University of Delaware, takes part in a Q&A to share the truth and science behind this “extra” day added to the Gregorian calendar every four years. Why do we have leap day? Unfortunately, the amount of time the earth takes to go around the sun is not exactly 365 days. It’s off by about ¼ of a day each year. It would be hard to have a calendar for 365 ¼ days. When was the extra day added to the calendar? Julius Caesar introduced the Julian calendar in 46 B.C., which added one extra day every four years. Of course, the year is not exactly 365 ¼ days either, so after a while, that extra time built up. Pope Gregory XIII established the Gregorian calendar [the current calendar] in 1582 to correct the fact that the calendar had gotten off by about 12 days, enough that it was noticeable. How was it noticeable? The seasons were gradually shifting, so that what we think of as summertime in the northern hemisphere had gradually become more like autumn. The shortest day of the year is Dec. 21. Basically, the shortest day of the year drifted and eventually was in early December. How did they institute the reforms? First, they skipped a couple of weeks, so they returned to the original calendar lining up with the sun and stars as it’s supposed to. Then they instituted a couple of rules to keep this from happening again. Leap year happens in years divisible by four, but every 100 years, there is not a leap year. However, every 400 years, you do have a leap year. This happened in the year 2000. And the next time it will happen most of us won’t be around — 2100 will not be a leap year. What would happen if the extra day had not been introduced? If we didn’t have it at all, we would be off by ¼ of a day every year. The seasons would completely shift through the calendar and anything that ties to the seasons would be affected, like farming. It would create havoc with the time to plant and to harvest crops, for example. You also would lose the meaning behind sayings such as “April showers bring May flowers.” Multiply the 2,000 years since it was introduced by ¼ day per year, and that would be 500 days we would have shifted over history. In the northern hemisphere January would have become summer, then gone back to being winter, then shifted off again. Does adding the extra day make up the difference exactly and keep the astral year in sync with the calendar year? Yes, but this relates to a bigger issue. Astronomers want time to match up so that the positions of the stars match up year after year. Because the length of day changes slightly over time, astronomers sometimes would like to add an extra “leap second” to keep the stars in sync with our time system. But adding a second is an annoyance for computer and tech systems. Did you know that people born on leap day are sometimes called “leaplings?” According to Google, in 2020, there were about 5 million people with Feb. 29 birthdays. Do you think they have any advantages or disadvantages to being born on this day? No, I didn’t know that, and I know someone who refused to be induced on that day because she didn’t want confusion for her child, although I think it might be cool. After all, in this day and age, everyone always knows how old they are. To set up an interview with Gizis, visit his profile and click on the contact button.

John Gizis

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Biography

John Gizis, a professor in Physics and Astronomy, focuses his research on improving understanding of stars and brown dwarfs. Gizis uses both ground-based and space-based telescopes to characterize the faint, cool objects.

Industry Expertise

Aerospace

Areas of Expertise

Brown Dwarfs and Binaries
Cool Stars
Stars
Solar System
Cosmology
Astronomy
Telescopes

Media Appearances

Delawareans will be treated to a partial eclipse on Aug. 21

WDDE-FM Online  online

2017-08-04

But while Delaware isn't on the path of totality, John Gizis, a physics and astronomy professor at the University of Delaware, says there is still something to look forward to in the First State.

“Many more people will see a partial solar eclipse. Here in Delaware, the moon will cover 80 percent of the sun, which is a lot but it’s not gonna make the really dramatic thing where day turns to night,” Gizis said.

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Esteemed UDel scientist Dr. Gizis talks space discoveries and aliens

The Tab  online

2017-05-08

Using technologies with gamma rays, scientists are planning to check to see if any other forms of intelligent life could be sending us messages using lasers.

As a dedicated professor to his University of Delaware students since 2001, Gizis agreed to sit down with The Tab and discuss his discoveries, his career, and, of course, aliens.

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UD professor made historic star discovery

The News Journal  online

2017-03-08

Yet, somehow, a star discovered by Gizis in 1999, nearly two decades ago, is host to not one, but seven Earth-like planetary objects, NASA recently announced. And it's only 40 light years, or 235 trillion miles, away.

That's close enough that it could be captured by the Kepler Telescope — raw data from the new system is scheduled to be released later Wednesday.

"I was very excited," Gizis said of the discovery. "And maybe a little bit jealous, too. Personally, it is an honor to have found something that came out in the long term."

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Articles

JWST/NIRCam Discovery of the First Y+Y Brown Dwarf Binary: WISE J033605.05-014350.4

The Astrophysical Journal

2023

We report the discovery of the first brown dwarf binary system with a Y dwarf primary, WISE J033605.05-014350.4, observed with NIRCam on JWST with the F150W and F480M filters. We employed an empirical point-spread function binary model to identify the companion, located at a projected separation of 0.″084, position angle of 295°, and with contrasts of 2.8 and 1.8 mag in F150W and F480M, respectively. At a distance of 10 pc based on its Spitzer parallax, and assuming a random inclination distribution, the physical separation is approximately 1 au. Evolutionary models predict for that an age of 1-5 Gyr, the companion mass is about 4-12.5 Jupiter masses around the 7.5-20 Jupiter mass primary, corresponding to a companion-to-host mass fraction of q = 0.61 ± 0.05. Under the assumption of a Keplerian orbit the period for this extreme binary is in the range of 5-9 yr. The system joins a small but growing sample of ultracool dwarf binaries with effective temperatures of a few hundreds of Kelvin. Brown dwarf binaries lie at the nexus of importance for understanding the formation mechanisms of these elusive objects, as they allow us to investigate whether the companions formed as stars or as planets in a disk around the primary.

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Deep drilling in the time domain with DECam: survey characterization

Monthly Notices of the Royal Astronomical Society

2023

This paper presents a new optical imaging survey of four deep drilling fields (DDFs), two Galactic and two extragalactic, with the Dark Energy Camera (DECam) on the 4-m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO). During the first year of observations in 2021, >4000 images covering 21 deg2 (seven DECam pointings), with ~40 epochs (nights) per field and 5 to 6 images per night per filter in g, r, i, and/or z have become publicly available (the proprietary period for this program is waived). We describe the real-time difference-image pipeline and how alerts are distributed to brokers via the same distribution system as the Zwicky Transient Facility (ZTF). In this paper, we focus on the two extragalactic deep fields (COSMOS and ELAIS-S1) characterizing the detected sources, and demonstrating that the survey design is effective for probing the discovery space of faint and fast variable and transient sources. We describe and make publicly available 4413 calibrated light curves based on difference-image detection photometry of transients and variables in the extragalactic fields. We also present preliminary scientific analysis regarding the Solar system small bodies, stellar flares and variables, Galactic anomaly detection, fast-rising transients and variables, supernovae, and active Galactic nuclei.

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Young Stellar Objects, Accretion Disks, and Their Variability with Rubin Observatory LSST

The Astrophysical Journal Supplement Series

2023

Vera C. Rubin Observatory, through the Legacy Survey of Space and Time (LSST), will allow us to derive a panchromatic view of variability in young stellar objects (YSOs) across all relevant timescales. Indeed, both short-term variability (on timescales of hours to days) and long-term variability (months to years), predominantly driven by the dynamics of accretion processes in disk-hosting YSOs, can be explored by taking advantage of the multiband filters option available in Rubin LSST, in particular the u, g, r, i filters that enable us to discriminate between photospheric stellar properties and accretion signatures. The homogeneity and depth of sky coverage that will be achieved with LSST will provide us with a unique opportunity to characterize the time evolution of disk accretion as a function of age and varying environmental conditions (e.g., field crowdedness, massive neighbors, metallicity) by targeting different star-forming regions. In this contribution to the Rubin LSST Survey Strategy Optimization Focus Issue, we discuss how implementing a dense observing cadence to explore short-term variability in YSOs represents a key complementary effort to the Wide-Fast-Deep observing mode that will be used to survey the sky over the full duration of the main survey (≈10 yr). The combination of these two modes will be vital to investigate the connection between the inner-disk dynamics and longer-term eruptive variability behaviors, such as those observed on EX Lupi-type objects.

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Education

Caltech

PhD

Astronomy

1997

Yale University

BS

Astronomy and Physics

1992

Languages

  • English