Astrophysics 280 Final
James Webb Space Telescope (JWST) has a primary mirror 6.5 meters in diameter. What is the diffraction limit of JWST at 650 nm? Give your answer in the form x.yEz
0.025
What is the angular size of the supergiant star Betelgeuse. Take the distance to Betelgeuse as 168 pc and the radius of Betelgeuse as 764 * (R_sun). 1 pc = 206,265 AU and R_sun = 7.0E8 m. GIve your answer in the form x.yEz.
0.042
What is the angular resolution of Hubble Space Telescope (HST) at a wavelength of 550 nm? The diameter of HST's primary mirror is 2.4 meters. Give your answer in units of arcsec and in the form x.yEz. There are 206265 arcsec in one radian.
0.058
Pluto and Charon make one orbit about their barycenter every 6.387 days. Pluto and Charon are separated by 19,600 km. Compute the combined mass of Pluto and Charon in units of lunar masses. Give your answer in the form x.y. G = 6.67E-11 Nm^2kg^-2 and the mass of the Moon is 7.35E22 kg.
0.2
Hubble Space Telescope (HST) has a f/24 primary mirror that is 2.4-meter in diameter. What is the scale of HST in mm/arcsec?
0.28
Mass of 51 Peg b What is the mass of 51 Peg b? It's parent star, 51 Peg, has a mass of 1.11 solar masses, speed about the barycenter of 56.04 m sec^-1, and a period about the barycenter of 4.231 days. Give your answer in jovian masses and in the form x.y. The mass of Jupiter is 1.9 x 10^27 kg and the mass of the Sun is 2.0 x 10^30 kg.
0.4
Compute the radius of Sirius B in units of Earth radii. The surface temperature of Sirius B is 25,000 K. The surface temperature of the Sun is 5,777 K. The luminosity of Sirius B is 0.056 of the Sun. Take the radius of the Sun as 7.0 x 10^8 m and the radius of the Earth as 6.4 x 10^6 m. Give your answer in the form x.yEz.
1.4
A pulsar is discovered with a mass of 2.0 solar masses and a diameter of 12 km. What is its shortest possible rotation period in seconds. Give your answer in the form x.yEz.
1.8E-4
Star A has m_A = 2.0 and Star B has m_B = 4.5. How many times brighter is Star A compared to Star B?
10
The brightest star in the night sky, Sirius, has a parallax of 0.377 arc sec. What is the distance to Sirius in light years?
10
Distance to Quasar Use your result from the previous question (80% of lightspeed) and Hubble's Law with H = 22 (km/sec) /(million light years) to compute the distance to the quasar in billions of lightyears. Take c = 3.0E5 km/sec. Give your answer as an integer.
11
Compute the escape velocity from the surface of the Earth. Take G = 6.67E-11 N m^2 kg-2, the mass of the Earth, m_E = 5.97E24 kg, and the radius of the Earth, r_E = 6.38E6 m. Give your answer in the form xy.z km sec^-1.
11.2
What wavelength photon in nm is necessary to excite an electron in the hydrogen atom from the n = 1 level to the n = 2 level? Give your answer in the form x.yEz.. 1 eV = 1.60E-19 J, h = 6.67E-34 J sec, c = 3.00E8 m sec^-1, 1 nm = 1E-9 m.
120
What wavelength photon in nm is necessary to excite an electron in the hydrogen atom from the n = 1 level to the n = 2 level? Give your answer in the form x.yEz.. 1 eV = 1.60E-19 J, h = 6.67E-34 J sec, c = 3.00E8 m sec^-1, 1 nm = 1E-9 m.
120.0
Suppose the H-alpha line of hydrogen with a wavelength of 656.4 nm in a laboratory is observed in the spectrum of a star at 656.7 nm. How fast is the star moving toward or away from Earth in km sec^-1? Take c = 3.0E5 km sec^-1.
140 km/sec away
The H-delta line of hydrogen has a wavelength of 410.2 nm when observed in the laboratory. If the H-delta line appears in a star's spectrum at 410.4 nm, what is the radial velocity of the star? Give your answer in km sec^-1 and to the nearest integer. Take c = 3.0E5km/sec. (away or towards us)
146.0 away
Suppose Star 1 has a surface temperature of 6,000 K and Star 2 has a surface temperature of 3,000 K. How many more times energy per second is coming out of one square meter of Star 1 compared to one square meter of Star 2? Give your answer to the nearest integer.
16.0
The bright star Antares in the constellation Scorpius has an apparent magnitude m = 0.87 and an absolute magnitude M = -5.28. Compute the distance to Antares in parsecs. Give your answer in the form x.yEz.
170
Comet Halley has a period of 76 years. What is its average distance from the Sun in AU? Give your answer to the nearest integer.
18
The star Rigel has a surface temperature of 12,100 K and the Sun has a surface temperature of 5,777 K. How many more times energy per second is coming out of one square meter of Rigel compared to the Sun? GIve your answer in the form x.yEz
19
Compute the wavelength in nm of a photon needed to excite the electron in the Bohr atom from n = 3 to n = 4. Give your answer in the form x.yEz. Remember, 1eV = 1.60E-19 J, h = 6.63 E-34 J sec, c = 3.00E8 m sec^-1
1900
Asteroid (17061) Tegler = 1999 GQ8 was discovered at Lowell Observatory in 1999. It has a semi-major axis of 2.54 AU, an eccentricity of 0.16, and an inclination of 4.2 degrees. What is the asteroid's perihelion distance in AU. Give your answer to one place to the right of the decimal point, e.g. x.y.
2.1(maybe supposed to be 3.4?)
Messier 4 (M4) is the nearest globular cluster. You observe a star with apparent magnitude m = 12.2 in the cluster. You know the star has absolute magnitude M = +0.5 What is the distance to the star, and so to the cluster, in parsecs. Give your answer in the form x.yEz.
2.2E3
Asteroid Tegler has a semi-major axis of 2.54 AU, an eccentricity of 0.16, and an inclination of 4.2 degrees. What is the asteroid's distance from the Sun in AU when its true anomaly is 60 degrees. Give your answer to one place to the right of the decimal point, e.g. x.y.
2.3
How much energy in eV does it take for an electron in a hydrogen atom to jump from the n = 2 level to the n = 4 level?
2.56
Supermassive Black Hole at the Center of the Galaxy The star S2 orbits the supermassive black hole at the center of the Milky Way Galaxy. The period of S2 about the black hole is 15.2 years. It's average distance (semi-major axis) is 840 AU. Estimate the mass of the black hole at the center of the Milky Way in units of solar masses. Give your answer in the form x.yE7.
2.6E6
Asteroid Tegler has a semi-major axis of 2.54 AU, an eccentricity of 0.16, and an inclination of 4.2 degrees. What is the asteroid's aphelion distance in AU. Give your answer to one place to the right of the decimal point, e.g. x.y.
2.9
https://photos.app.goo.gl/2g1fTifApbtRK7LK9 You take a spectrum of a star and find it has a KO spectral type (temperature) and is a giant (luminosity class of III). You measure the apparent magnitude of the star and find it has m = +1.6. Use the technique of spectroscopic parallax to find the distance to the star in parsecs. Give your answer in the form x.yEz.
21
Asteroid Tegler has a semi-major axis of 2.54 AU, an eccentricity of 0.16, and an inclination of 4.2 degrees. What is the asteroid's orbital velocity in km sec^-1 when it is at a true anomaly of 60 degrees? . Give your answer to the nearest integer
21 (maybe supposed to be 53?)
Use the Virial Theorem (-2K = U) to estimate the mean temperature inside the Sun. Assume the Sun is a sphere and has a uniform density and so has a gravitational potential energy of (-3/5)(GM^2/R). Assume all the hydrogen is fully ionized, so the mass of one hydrogen atom (1 amu) is shared between two particles (the H nucleus and the free electron), and the mean mass per particle is 1 amu per 2 particles, or µ = 0.5. Take the radius of the Sun as R = 7.0E8 m and the mass of the Sun as M = 2.0E30 kg. Take G = 6.67E-11 Nm^2kg^-2, k = 1.38E-23 JK^-1, and m_H = 1.67E-27kg. Give your answer in the form x.yEz.
2300000
The star Rigel has a surface temperature of 12,100 K. At what wavelength in nm does Rigel put out the most energy? Give your answer in the form x.yEz.
240
The brightest star in the sky, Sirius (aka Alpha Canis Majoris), has an apparent magnitude of -1.5. Mirzam (aka Beta Canis Majoris) has an apparent magnitude of +2.0. How many times brighter is Sirius than Mirzam? GIve your answer in the form x.yEz
25
The brightest star in the sky, Sirius (aka Alpha Canis Majoris), has an apparent magnitude of -1.5. Mirzam (aka Beta Canis Majoris) has an apparent magnitude of +2.0. How many times brighter is Sirius than Mirzam? GIve your answer in the form x.yEz.
25
What is the apparent magnitude, m, of a solar-like star (M =+5.0) in the Andromeda galaxy. Take the distance to Andromeda to be 610,000 pc (2,000,000 ly). Give your answer to the nearest integer.
29
Energy in 400 nm photon Blue light has a wavelength of 400 nm. How much energy in eV is in a single photon with a wavelength of 400 nm. 1eV = 1.6E-19 J
3.1
Compute the radius of a cloud. Mass density 3.3E-17kgm^-3. Temperature is 10k. Jeans mass is 1.47E31.
3.2E4 AU
For how many years does a 25 solar mass star convert hydrogen to helium in its core. Give your answer in the form x.yEz.
3.2E6
Consider the cold dense core inside a dark cloud. The cloud has a radius R and a temperature T = 10 K. The cloud is primarily composed of H2 molecules (� = 2 ) with a constant number density of 1.0E10 molecules E-3 throughout the cloud. a) Compute the mass density of the cloud in units of kg m-3
3.3E-17
Europa orbits Jupiter at an average distance of about 6.7E5 km from the center of the planet. Jupiter has a mass of 1.9E27 kg. What is the period of Europa about Jupiter in units of days. Give your answer in the form x.y
3.5
A white dwarf has a surface temperature of 25,000 K and the Sun has a surface temperature of 5,777 K. How many more times energy per second is coming out of one square meter of the white dwarf l compared to the Sun? GIve your answer in the form x.yEz
3.5E2
What is the radius of event horizon surrounding a 10 solar mass black hole, i.e., what is the value of the Schwarzschild radius. GIve your answer in units of km and in the form x.yEz.
30
Event Horizon What is the radius of the event horizon for an 11 solar mass black hole. Give your answer to the nearest integer in units of km.
33
Image Size of Full Moon Made By Lutz Telescope The Lutz telescope has a scale of 0.020 mm arcsec^-1. The full Moon has an angular size of 30 arcmin. How large will an image of the full Moon be in the focal plane of the Lutz telescope? Give your answer to the nearest integer mm.
36
If the angular size of ISS is 40 arc sec in the image shown in the article and the linear size of ISS is 134 meters, use the small-angle formula to compute how far away ISS was from me when I captured the image (miles)
432
For the Coma cluster of galaxies, we OBSERVE v = 3.3 x 10^6 m sec-1 and r = 3.8 x 10^22 m. Find the total mass of the Coma cluster in units of solar masses. Take G = 6.67 x 10-11 N m2 kg-2 and 1 solar mass = 2.0 x 10^30 kg.
6.2E15
Which technique below was first used to discover dark matter?
Observing the motions of galaxies in the Coma Cluster of galaxies and applying the Virial Theorem
Type II Supernova
Shock wave blowing the outer envelope of a star into space
If you wanted to observe the youngest stars in the Milky Way Galaxy, which type of cluster would be best to observe?
A stellar association
Type la Supernova
Collapse and explosion of a white dwarf
Which of the following statements about main sequence stars is FALSE?
During the main sequence, the power output by a star is the result of fusion of helium into carbon in the core of the star.
Nova
Fusion of hydrogen to helium on surface of a white dwarf
If hydrogen is the most common element in the Universe, why do we not see the lines of hydrogen in the spectra of the hottest stars?
In the hottest stars, hydrogen atoms are ionized, and so there are no electrons to produce lines in the spectrum.
Results of Graduate Student Analysis of a Stellar Spectrum A graduate student did a careful analysis of a star's spectrum. She found HeI (neutral helium) lines were the strongest lines in the spectrum. HI (neutral hydrogen) had the next strongest lines followed by SiIII (doubly ionized Silicon). From her analysis, she can conclude: https://photos.app.goo.gl/ZX4g7uKPS7t1HNuaA
The temperature of the star in near 25,000 K
If you trace back the history of the carbon atoms in your body through all of cosmic history, where did most of the carbon atoms likely originate?
They were fused from three helium nuclei in the cores of red gaints before the Sun came into existence.
Nucleosynthesis If stars with masses like our Sun cannot make elements heavier than oxygen, where do the heavy elements like iron originate?
They were made in the really hot cores of stars much more massive than the Sun.
Below is a schematic of a spectrograph. Which element disperses light?
grating
Consider two telescopes each with a primary mirror 1-meter in diameter. Telescope #1 has f/2.0 and telescope #2 has f/9.0. If all circumstances of an observation of Jupiter were the same between the two telescope (e.g. the same exposure time, same detectors on the telescopes etc. ), which telescope would give a brighter image of Jupiter?
telescope #2 with f/9.0
Which of the following stellar properties determine the intrisinsic luminosity of a star
temperature, and radius
On a Hertzsprung-Russell diagram, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age?
the point on the main sequence where stars begin to move toward the red giant region (turn off point)
For a white dwarf with a surface temperature of 25,000 K, what type of electromagnetic energy does it put out the most?
ultraviolet
A comet is 10 AU from the Sun with an orbital velocity relative to the Sun of 30 km/sec. Is this comet from another planetary system? Take M_sun = 2.0E30 kg and 1 AU = 1.5E11 m.
yes
James Webb Space Telescope (JWST) has a primary mirror 6.5 meters in diameter. Betelgeuse has a radius 890 times that of the Sun and is 220 pc away from the Earth. Will JWST be able to resolve the disk of Betelgeuse at 650 nm. Take the radius of the Sun as 7.0 x 10^8 m. 1 pc = 206,265 AU and 1 AU = 1.5 x 10^11 m. Take care about radius and diameter in this problem.
yes
HST and the Pluto-Charon System Can HST spatially resolve Pluto and its largest satellite Charon? Take the distance between Pluto and Charon as 20,000 km, and the distance between the Earth and the Pluto-Charon system as 39 AU. 1 AU = 1.5E8 km.
yes (hubble is .048arcsec, pluto-charon is .71)
Evolution into a Giant A star becomes a giant when its outer layers expand. Where does the energy come from to expand the outer layers?
it runs out of fuel in the core, and starts burning it in the shell, and therefore it expands because gravity is lesser there
Suppose the electron in the above question is moving in a circular orbit of radius r about the proton. Using the virial theorem (-2K = U) compute the kinetic energy of the electron in terms of k, e, and r. Show your work
ke^2/2r
Lutz Telescope Field of View and the Moon The CCD sensor in the focal plane of the Lutz telescope is 13.3 mm x 13.3 mm. Will an image of the full Moon fit on the CCD sensor?
no
Two stars have an angular separation of 0.01 arcsec. Is it possible for HST to resolve the two stars at a wavelength of 550 nm?
no
Kepler's First Law says
planets orbit the Sun on elliptical orbits
Which type of telescope uses a mirror as its main element to collect light?
reflector
Who discovered dark matter?
Zwicky
What is the apparent magnitude, m, of a solar-like star (M =+5.0) in the Andromeda galaxy. Take the distance to Andromeda to be 610,000 pc (2,000,000 ly). Give your answer to the nearest integer.The brightness of the star is the above question
(29) Is at the limit of our ability to detect
A white dwarf star has a surface temperature of 25,000 K. At what wavelength in nm does the white dwarf put out the most energy? Give your answer in the form x.yEz.
1.2E2
Deneb has an apparent magnitude m = +1.26 and is 490 pc from the Earth. What is the absolute magnitude M of Deneb? Give your answer in the form x.y
-7.2
Starting with Coulomb's Law, F = kq1q2/r2, derive the potential energy, U, of an electron of charge -e at a distance r from a proton of charge +e. Hint: Follow the steps we used in class to derive the potential energy of a mass m at a distance r from a mass M. Show your work. Give your answer in terms of k, e, and r
-ke^2/r
Crab Neutron Star's Smallest Possible Rotation Period What is the smallest possible rotation period (fastest rotational speed) of the Crab neutron star in seconds. Take the mass of the neutron star as 1.4 solar masses and its radius as 9 km. G = 6.67E-11 N m^2 kg^-2 and M_sun = 2.0E30 kg. Give your answer in the form x.yEz.
0.00039
Crab Neutron Star's Smallest Possible Rotation Period What is the smallest possible rotation period (fastest rotational speed) of the Crab neutron star in seconds. Take the mass of the neutron star as 1.4 solar masses and its radius as 9 km. G = 6.67E-11 N m^2 kg^-2 and M_sun = 2.0E30 kg. Give your answer in the form x.yEz.
0.00039
The Atacama Large Millimeter/Sub-millimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile. It is at the highest altitude of any observatory on the Earth. Compute the atmospheric pressure at ALMA. Give your answer as a fraction of atmospheric pressure at sea level. In other words, compute P/Po where P is the atmosphere pressure at ALMA and Po is the atmospheric pressure at sea level. Take the altitude of ALMA 5,000 m (16,500 ft)), T = 60 F (289 K), and an atmosphere composed entirely as N2, i.e., μ=28. Take k = 1.38E-23 J/K, g = 9.81 ms-2, and m_H = 1.67E-27 kg. Give your answer in the form x.yEz
0.56
Speed of Recession You observe a quasar with a redshift of z = 1.0 What fraction of the speed of light is the recession speed of the quasar, i.e. compute v/c. Take c = 3.0 x 105 km/sec
0.6
You observe a quasar with a redshift of z = 2.0. What fraction of the speed of light is the recession speed of the quasar, i.e., compute v/c. Take c = 3.0 x 105 km/sec. Give your answer in the form 0.x, i.e., one place to the right of the decimal point.
0.8
A brown dwarf is a substellar object that did not have enough mass to produce nuclear fusion in its core and become a main sequence star. You observe a brown dwarf and measure its luminosity as 1/100,000 that of the Sun and its surface temperature as 1,000 K. Compute the radius of the brown dwarf in units of Jupiter radii. Take T_sun = 5,777 K, R_sun = 7.0 E8 m, and R_jup = 7.1 E7 m
1
Hubble's Law You obtain a spectrum of a galaxy and find it has a redshift and a recession velocity of 22,000 km/sec. How far away is the galaxy in billions of lightyears? Use H = 22 km sec^-1 million-light-years^-1. Give your answer as an integer.
1
Cluster Age You measure the luminosities and surface temperature of stars in a cluster and discover the turn-off point on its H-R diagram occurs for stars with a mass 1.4 times that of the Sun. How old is the cluster? Give your answer in years and the form x.yEz.
4E9
You measure the luminosities and surface temperature of stars in a cluster and discover the turn-off point on its H-R diagram occurs for stars with a mass 1.4 times that of the Sun. How old is the cluster? Give your answer in years and the form x.yEz
4E9
Weather satellites are often placed in geosynchronous orbits above the Earth. These are orbits where satellites can remain fixed above a certain point on the surface of the Earth. What must be the altitude of such satellites in units of Earth radii. Give your answer to an accuracy of one place to the right of the decimal point.
5.6
If a person on Earth has a weight of 150 lbs, what is their weight on Mars in lbs. Take the mass of Mars as 6.4E23 kg and the radius of Mars as 3.4E6 m. Give your answer to the nearest integer.
57
Hubble Space Telescope (HST) has a f/24 primary mirror that is 2.4-meter in diameter. What is its focal length in mm?
58000
Power of a Quasar How many solar masses per year must a supermassive black hole devour to power a quasar 1.0E4 times brighter than the typical galaxy. Take the typical galaxy to have a brightness of 1.0E10 Suns. L_Sun = 3.8E26 Joules/sec. Give your answer in the form x.yEz.
66
Computing the Distance to Andromeda Using a Cepheid Variable Star Edwin Hubble made observations of a Cepheid variable star in the Andromeda Galaxy. He found the star had a period of 32 days and an average apparent magnitude of m = 18.5. Use these data, what is the distance to the Andromeda Galaxy in parsecs. Give your answer in the form x.yEz.
6E5-6.5E5
Use your result from the above question and Hubble's Law with H = 22 (km/sec) /(million light years) to compute the distance to the quasar in lightyears. Take c = 3 E5 km/sec. Give your answer in the form x.yEz.
8.18E9
Hubble's Law You obtain a spectrum of a galaxy and find it has a redshift and a recession velocity of 18,000 km/sec. How far away is the galaxy in million of lightyears? Use H = 22 km sec^-1 million-light-years^-1
818
A star exhibits a H-alpha absorption line at 658 nm in its spectrum. If H-alpha has a laboratory (rest) wavelength of 656 nm and c = 3.0 x 10^8 m sec^-1, what the radial speed of the star in km sec^-1? (away or towards)
9.2E2 away
You observe a young open cluster and find the typical speed of a star in the cluster is 1 km/sec and the average separation between the stars is 2 pc. Assume all of the stars have the same mass and that there are N(N-1)/2 possible pairings of stars. Assume all the stars in the cluster are gravitationally bound to each other. Use the Virial Theorem to compute the mass of the cluster in solar masses. 1 pc = 206,265 AU and 1 AU = 1.5 E11 m and M_sun = 2.0E30 kg and G = 6.67E11 N m^2 kg^-2. Give your answer in the form x.yEz
930
You observe a young open cluster and find the typical speed of a star in the cluster is 1 km/sec and the average separation between the stars is 2 pc. Assume all of the stars have the same mass and that there are N(N-1)/2 possible pairings of stars. Assume all the stars in the cluster are gravitationally bound to each other. Use the Virial Theorem to compute the mass of the cluster in solar masses. 1 pc = 206,265 AU and 1 AU = 1.5 E11 m and M_sun = 2.0E30 kg and G = 6.67E11 N m^2 kg^-2. Give your answer in the form x.yEz.
930
The typical healthy human body has a temperature of 98.6 F or 310 K. At what wavelength does the human body emit the largest amount of energy. Give your answer in units of microns. 1 micron = 1.0E-6 meters. Give your answer in the form x.yEz.
9400
Hubble Space Telescope is in a nearly circular orbit 610 km (380 miles) above the surface of the Earth. Compute its orbital period. GIve your answer in minutes to the nearest integer.
97
The Solar System is moving around the center of the Milky Way Galaxy in an approximately circular orbit of radius 26,400 light-years with a velocity of 220 km s-1. What is the mass at the center of the Milky Way Galaxy? Take G = 6.67E-11 N m^2kg^-2, 1 ly = 9.46E15 m, and the mass of the Sun, M_S = 2.00E30 kg. Give your answer in units of solar masses, scientific notation, and no places to the right of the decimal point, e.g. xEyz
9E10
Research your spectral types
:)
What is a White Dwarf
About 1 solar mass in volume about that of Earth
Neutron Star
About 1.4 to 3 solar masses in volume 10 -15 km in diamter
Stars in the neighborhood of the Sun (i.e., near the Sun in space, not on the H-R diagram) are dominated by
M5 V stars
Which of the following have been put forth to describe dark matter?
MACHO, WIMP, SIMP, IDK
Black Hole
More than 3 solar masses of material in zero
Hubble Space Telescope (HST) has a f/24 primary mirror that is 2.4-meter in diameter. HST has a CCD array in its focal plane that is 61 mm x 61 mm, would the Ring Nebula with an angular size in the sky of 230 arcsec x 230 arcsec fit on HST's CCD array?
The Ring Nebula would almost fit on the CCD sensor.
A main sequence star becomes a giant star when its outer layers expan. Where does the energy come from to expand the outer layers
The conversion of hydrogen into helium in a shell surrounding the core of the star
Supernova It is likely that the many supernova explosions that happened in the Milky Way Galaxy played a role in the evolution of life over billions of years. How would they have influenced the development of life on Earth?
The cosmic rays produced by supernova explsions would have contributed to the rate of mutations over many generations
The figure below represents an infinitesimally small cylindrical volume at some radial distance r from the center of the Sun. What balances the inward force of gravity on the material in the volume?
The difference between the larger outward pressure Po at the bottom of the cylinder and the smaller inward pressure on the top of cylinder P
Each of the Keck Telescopes has a primary mirror f 10.0 meters in diameter and a focal length of 17.5 meters. What is the focal ratio of a Keck Telescope?
f/1.8
Power Source of a Quasar How many solar masses per year must a supermassive black hole devour to power a quasar 1.0E3 times brighter than the typical galaxy. Take the typical galaxy to have a brightness of 1.0E10 Suns. L_Sun = 3.8E26 Joules/sec. Give your answer in the form x.yEz
idk but hopefully 4.2E23 (don't forget to multiply in correct time and divide by solar mass)