DOCSLIB.ORG

Infrared Photometry and Radiometry of the Planets

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Infrared Photometry and Radiometry of the Planets RICE UNIVERSITY INFRARED PHOTOMETRY AND RADIOMETRY OF THE PLANETS by Kendall Ray Armstrong A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE Thesis Director's signature: Hous ton, Texa s May, 1971 ABSTRACT INFRARED PHOTOMETRY AND RAD I OME'TRY OF THE PLANETS by Kendall R. Armstrong The first observations of the planets Venus, Jupiter, and Saturn have been made in the far infrared at wavelengths between 304 and 3004 using the Rice University Flying Infrare Telescope and crystal transmission filters cooled to liquid He temperatures. Wide band brightness temperatures have been found for the three planets which vary significantly from their calculated and observed effective temperatures. Photometric observations at wavelengths less than 254 obtained at the University of Arizona Catalina Observatory complete the near infrared spectrum of Venus, Mars, Jupiter, Saturn, Uranus, Vesta, the Galilean satellites,- and Titan. Results at 10.24 and 224 indicate tenuous atmospheres on the satellites Jupiter I and Titan. Millimeter radio- matry gives a 1.2 mm brightness temperature of 103(±32)K for Uranus. It is shown from high resolution scans that the high 54 brightness temperature of Jupiter originates below the visible cloud tops in the region of the north equatorial belt. High resolution photometry of the Saturn system shows that the rings radiate a significant fraction of the flux observed at 10.2b and at 22b radiate over half the flux observed from the dish-rings system. TABLE OF CONTENTS Page 1.0 INTRODUCTION 1 2.0 THE NEAR INFRARED PHOTOMETRY 3 3.0 FAR INFRARED RADIOMETRY 8 3.1 The Far Infrared Filters 8 3.2 The Observations 13 4.0 OTHER OBSERVATIONS 21 4.1 Millimeter Radiometry 21 4.2 High Resolution Photometry of Jupiter and Saturn -22 5~ 0 DISCUSSION 2 5 5.1 The Planets 27 5.1. a. Mercury 27 5.1. b. Venus 23 5.1. c. Mars 33 5.1. d. Jupiter 34 5.1. e. Saturn 39 5.1. f. Uranus and Neptune 45 5.2 The Satellites 46 5.2. a. Asteroid Vesta 46 5.2. b. The Galilean Satellites 49 5.2. c. Titan 52 6.0 CONCLUSIONS 54 FIGURE CAPTIONS 59 ACKNOWLEDGEMENTS 63 REFERENCES 65 1 1. INTRODUCTION The. infrared spectrum from approximately 5U to 300p. is the most important region of the spectrum in the astronomical study of planetary atmospheres and is a powerful tool in understanding the composition of the atmospheres and planetary surfaces. Reflection spectroscopy in the region below 3U has been used to determine much of the composition and physical state of the upper atmosphere of the planets, but since it depends directly on incident solar radiation rather than radiation originating from the planet itself, does not give the information necessary to construct physical models of the planets' atmospheres and interiors. Planetary radiation in the thermal region of the spectrum has bean absorbed and redistributed by the planet before being reradiated, and observations of the brightness temperature over the complete spectrum serve as the boundary conditions, as wall as dictate which processes are most important, for the problem in radiation transfer which must be solved in the construction of planetary models. Questions such as the He : H2 abundance ratio for Jupiter and Saturn can be answered by remote observation only through measurements in the far infrared region because of the spectroscopic inactivity resulting from the symmetric, 2 homonuclear molecular structure of He. The observation of the far infrared spectra of Venus, Jupiter, and Saturn between 30|J. and 300P is the most important result of this research. Two factors have made these observations possible: the use of a flying infrared telescope mounted in an aircraft and flown above the tropo¬ sphere to overcome the strong water vapor absorption band in the far infrared region; and the development of a system of He cooled crystal filters which have well defined, high transmission pass bands. These observations fill in the most significant portion of the gap between 25H and milli¬ meter wavelengths for which ground-based astronomy is impossible. Numerous ground based photometric observations have been reduced to complete the thermal spectra of the planets and extend the known spectra of the Galilean satellites and Titan to 251-i. Radiometric observations of the planets at 1.2 mm and'high spatial resolution photometry of Jupiter and Saturn are also used in the interpretation of the planetary spectra. 3 2.0 THE NEAR INFRARED PHOTOMETRY Ground based observations in the near infrared are limited by the atmosphere to a few specific windows in the electromagnetic spectrum through which incident radiation is transmitted with relatively little atten¬ uation. These windows occur at wavelengths less than about 25b betv/een the strong rotational absorption bands of several atmospheric gases, mainly H^O, CO^ and Og (Howard and Garing, 1962). Between 25p and 1mm the lower atmosphere is made almost opaque by the rotational band of water vapor at 100P. The KLMNQ photometry used for this research was obtained in five windows centered near 2.2, 3.4, 5.0, 10.2 and 22p. Observations of the planets and satellites were made with the 28-inch, 60-inch and 61-inch telescopes at the Catalina Observatory during the regular photometric observing program described by Johnson and Mitchell (1962). Briefly, each observation is initiated by entering onto paper tape, from a punched observing card and from the photometer, the following data: the identification number of the object; the right ascension and declination of the object, the date and time of the observation; the integration time; the identification number of the filter 4 being used? and the amplifier gain setting. Integrations (usually 15 seconds) of alternate deflections from the object and sky are punched onto the tape and continued until the observer feels sufficient accuracy has been obtained. After each block of integrations the time at the end of the observation and the quality of the observation ("good" or "bad") as judged by the observer are entered onto the paper tape. The observations for each night are fed into a digi¬ tal computer and are reduced according to a standard procedure (Johnson and Mitchell, 1962). The computing program checks the assumed atmospheric extinction co¬ efficient for each filter passband from observations of 1 standard stars during the night, and if warranted, new coefficients are computed from observations of one or more of the standard stars. The observed relative magni¬ tudes are transformed to their values in the absence of atmospheric extinction, and then converted to fluxes using the absolute calibration of the filters (Johnson, 1965a; Low ejt al., 1970) . The planets Venus, Mars, Jupiter, Saturn, and Uranus? the asteroid Vesta; and the satellites J I (Io), J II (Europa), J III (Ganymede), J IV (Callisto) . 5 and Titan have been observed under the program outlined above. Most of the observations were made during the period January-May, 1969; a few observations at 5p and 22\x were made in February, March, and November, 1968. Measurements at 2.2li and 3.4|i are included in the observations made after January, 1970. Because the planetary observations were made during the regular stellar observing program, the beam diameter of the telescope was usually smaller than or approximately the same size as the visible disks of Venus, Jupiter and Saturn. In such cases errors of 20-30% may be intro¬ duced when calculating brightness fluxes, since the exact shape of the beam and its position on the planetary disk is not well known. Even in the absence of uncertaint¬ ies in beam size and pointing, the surface brightness would not be expected to remain constant from one observ¬ ation to the next because of the curvature of the plane¬ tary surface, limb darkening effects, and real temperature variations across the planetary surface. Only on five nights from February 22 to March 8, 1967, when a beam diameter of 180 arcsec was used, do the brightness temp¬ eratures obtained correspond to the total flux emitted by the visible planetary hemisphere. 6 All data obtained at 5n during the first five months of 1969 have been disregarded in the computation of brightness temperatures because of a leak near 12p in the 5|i filter used at that time. The basic filter had half-power points at 4.57|_i and 5.42^ with less than .02% transmission from 2.Op to 4.0ji and from 5.8p to 7.Op. Barium Fluoride was used to provide blocking beyond 13n; however, a leak was discovered at 12u which passed ap¬ proximately 11% of the flux transmitted by the N filter. Sapphire, which has good blocking beyond 7{j., was substi¬ tuted for the BaF2 to eliminate this leak. The monochromatic flux received from the projected disk of a. spherical planet of radius R in radiative equi¬ librium with solar radiation at an orbital distance r from the earth, with a telescope beam having a radius 3$. < R at distance r, is given by „ „ TTR^ ,a\ 2 TT&rtf2 „ -2-2 -1 -1-1 F = B w cm 1 str d-1) \ \ 2 ("a' TTR2 I- ' where is the monochromatic intensity of flux emitted from the surface of the planet and "a is the average orbital radius of the planet. The monochromatic surface brightness is then, 2 2 2 1 Wx = TTBX = Fx (f) (|) (f) W cm-V (1-2) where to is the planetary diameter in radians and a is 7 the telescope beam width, with the understanding that tu/a = 1 for a > UJ. The results of the KLMNQ photometry for each of the planets and satellites are summarized in Table 1.
Load more

Recommended publications
  • CIE Technical Note 004:2016
    TECHNICAL NOTE The Use of Terms and Units in Photometry – Implementation of the CIE System for Mesopic Photometry CIE TN 004:2016 CIE TN 004:2016 CIE Technical Notes (TN) are short technical papers summarizing information of fundamental importance to CIE Members and other stakeholders, which either have been prepared by a TC, in which case they will usually form only a part of the outputs from that TC, or through the auspices of a Reportership established for the purpose in response to a need identified by a Division or Divisions. This Technical Note has been prepared by CIE Technical Committee 2-65 of Division 2 “Physical Measurement of Light and Radiation" and has been approved by the Board of Administration as well as by Division 2 of the Commission Internationale de l'Eclairage. The document reports on current knowledge and experience within the specific field of light and lighting described, and is intended to be used by the CIE membership and other interested parties. It should be noted, however, that the status of this document is advisory and not mandatory. Any mention of organizations or products does not imply endorsement by the CIE. Whilst every care has been taken in the compilation of any lists, up to the time of going to press, these may not be comprehensive. CIE 2016 - All rights reserved II CIE, All rights reserved CIE TN 004:2016 The following members of TC 2-65 “Photometric measurements in the mesopic range“ took part in the preparation of this Technical Note. The committee comes under Division 2 “Physical measurement of light and radiation”.
    [Show full text]
  • Fundametals of Rendering - Radiometry / Photometry
    Fundametals of Rendering - Radiometry / Photometry “Physically Based Rendering” by Pharr & Humphreys •Chapter 5: Color and Radiometry •Chapter 6: Camera Models - we won’t cover this in class 782 Realistic Rendering • Determination of Intensity • Mechanisms – Emittance (+) – Absorption (-) – Scattering (+) (single vs. multiple) • Cameras or retinas record quantity of light 782 Pertinent Questions • Nature of light and how it is: – Measured – Characterized / recorded • (local) reflection of light • (global) spatial distribution of light 782 Electromagnetic spectrum 782 Spectral Power Distributions e.g., Fluorescent Lamps 782 Tristimulus Theory of Color Metamers: SPDs that appear the same visually Color matching functions of standard human observer International Commision on Illumination, or CIE, of 1931 “These color matching functions are the amounts of three standard monochromatic primaries needed to match the monochromatic test primary at the wavelength shown on the horizontal scale.” from Wikipedia “CIE 1931 Color Space” 782 Optics Three views •Geometrical or ray – Traditional graphics – Reflection, refraction – Optical system design •Physical or wave – Dispersion, interference – Interaction of objects of size comparable to wavelength •Quantum or photon optics – Interaction of light with atoms and molecules 782 What Is Light ? • Light - particle model (Newton) – Light travels in straight lines – Light can travel through a vacuum (waves need a medium to travel in) – Quantum amount of energy • Light – wave model (Huygens): electromagnetic radiation: sinusiodal wave formed coupled electric (E) and magnetic (H) fields 782 Nature of Light • Wave-particle duality – Light has some wave properties: frequency, phase, orientation – Light has some quantum particle properties: quantum packets (photons). • Dimensions of light – Amplitude or Intensity – Frequency – Phase – Polarization 782 Nature of Light • Coherence - Refers to frequencies of waves • Laser light waves have uniform frequency • Natural light is incoherent- waves are multiple frequencies, and random in phase.
    [Show full text]
  • The University of Chicago Glimpses of Far Away
    THE UNIVERSITY OF CHICAGO GLIMPSES OF FAR AWAY PLACES: INTENSIVE ATMOSPHERE CHARACTERIZATION OF EXTRASOLAR PLANETS A DISSERTATION SUBMITTED TO THE FACULTY OF THE DIVISION OF THE PHYSICAL SCIENCES IN CANDIDACY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF ASTRONOMY AND ASTROPHYSICS BY LAURA KREIDBERG CHICAGO, ILLINOIS AUGUST 2016 Copyright c 2016 by Laura Kreidberg All Rights Reserved Far away places with strange sounding names Far away over the sea Those far away places with strange sounding names Are calling, calling me. { Joan Whitney & Alex Kramer TABLE OF CONTENTS LIST OF FIGURES . vii LIST OF TABLES . ix ACKNOWLEDGMENTS . x ABSTRACT . xi 1 INTRODUCTION . 1 1.1 Exoplanets' Greatest Hits, 1995 - present . 1 1.2 Moving from Discovery to Characterization . 2 1.2.1 Clues from Planetary Atmospheres I: How Do Planets Form? . 2 1.2.2 Clues from Planetary Atmospheres II: What are Planets Like? . 3 1.2.3 Goals for This Work . 4 1.3 Overview of Atmosphere Characterization Techniques . 4 1.3.1 Transmission Spectroscopy . 5 1.3.2 Emission Spectroscopy . 5 1.4 Technical Breakthroughs Enabling Atmospheric Studies . 7 1.5 Chapter Summaries . 10 2 CLOUDS IN THE ATMOSPHERE OF THE SUPER-EARTH EXOPLANET GJ 1214b . 12 2.1 Introduction . 12 2.2 Observations and Data Reduction . 13 2.3 Implications for the Atmosphere . 14 2.4 Conclusions . 18 3 A PRECISE WATER ABUNDANCE MEASUREMENT FOR THE HOT JUPITER WASP-43b . 21 3.1 Introduction . 21 3.2 Observations and Data Reduction . 23 3.3 Analysis . 24 3.4 Results . 27 3.4.1 Constraints from the Emission Spectrum .
    [Show full text]
  • Variable Star Photometry with a DSLR Camera
    Variable star photometry with a DSLR camera Des Loughney Introduction now be studied. I have used the method to create lightcurves of stars with an amplitude of under 0.2 magnitudes. In recent years it has been found that a digital single lens reflex (DSLR) camera is capable of accurate unfiltered pho- tometry as well as V-filter photometry.1 Undriven cameras, Equipment with appropriate quality lenses, can do photometry down to magnitude 10. Driven cameras, using exposures of up to 30 seconds, can allow photometry to mag 12. Canon 350D/450D DSLR cameras are suitable for photome- The cameras are not as sensitive or as accurate as CCD try. My experiments suggest that the cameras should be cameras primarily because they are not cooled. They do, used with quality lenses of at least 50mm aperture. This however, share some of the advantages of a CCD as they allows sufficient light to be gathered over the range of have a linear response over a large portion of their range1 exposures that are possible with an undriven camera. For and their digital data can be accepted by software pro- bright stars (over mag 3) lenses of smaller aperture can be grammes such as AIP4WIN.2 They also have their own ad- used. I use two excellent Canon lenses of fixed focal length. vantages as their fields of view are relatively large. This makes One is the 85mm f1.8 lens which has an aperture of 52mm. variable stars easy to find and an image can sometimes in- This allows undriven photometry down to mag 8.
    [Show full text]
  • Chapter 4 Introduction to Stellar Photometry
    Chapter 4 Introduction to stellar photometry Goal-of-the-Day Understand the concept of stellar photometry and how it can be measured from astro- nomical observations. 4.1 Essential preparation Exercise 4.1 (a) Have a look at www.astro.keele.ac.uk/astrolab/results/week03/week03.pdf. 4.2 Fluxes and magnitudes Photometry is a technique in astronomy concerned with measuring the brightness of an astronomical object’s electromagnetic radiation. This brightness of a star is given by the flux F : the photon energy which passes through a unit of area within a unit of time. The flux density, Fν or Fλ, is the flux per unit of frequency or per unit of wavelength, respectively: these are related to each other by: Fνdν = Fλdλ (4.1) | | | | Whilst the total light output from a star — the bolometric luminosity — is linked to the flux, measurements of a star’s brightness are usually obtained within a limited frequency or wavelength range (the photometric band) and are therefore more directly linked to the flux density. Because the measured flux densities of stars are often weak, especially at infrared and radio wavelengths where the photons are not very energetic, the flux density is sometimes expressed in Jansky, where 1 Jy = 10−26 W m−2 Hz−1. However, it is still very common to express the brightness of a star by the ancient clas- sification of magnitude. Around 120 BC, the Greek astronomer Hipparcos ordered stars in six classes, depending on the moment at which these stars became first visible during evening twilight: the brightest stars were of the first class, and the faintest stars were of the sixth class.
    [Show full text]
  • Basics of Photometry Photometry: Basic Questions
    Basics of Photometry Photometry: Basic Questions • How do you identify objects in your image? • How do you measure the flux from an object? • What are the potential challenges? • Does it matter what type of object you’re studying? Topics 1. General Considerations 2. Stellar Photometry 3. Galaxy Photometry I: General Considerations 1. Garbage in, garbage out... 2. Object Detection 3. Centroiding 4. Measuring Flux 5. Background Flux 6. Computing the noise and correlated pixel statistics I: General Considerations • Object Detection How do you mathematically define where there’s an object? I: General Considerations • Object Detection – Define a detection threshold and detection area. An object is only detected if it has N pixels above the threshold level. – One simple example of a detection algorithm: • Generate a segmentation image that includes only pixels above the threshold. • Identify each group of contiguous pixels, and call it an object if there are more than N contiguous pixels I: General Considerations • Object Detection I: General Considerations • Object Detection Measuring Flux in an Image • How do you measure the flux from an object? • Within what area do you measure the flux? The best approach depends on whether you are looking at resolved or unresolved sources. Background (Sky) Flux • Background – The total flux that you measure (F) is the sum of the flux from the object (I) and the sky (S). F = I + S = #Iij + npix " sky / pixel – Must accurately determine the level of the background to obtaining meaningful photometry ! (We’ll return to this a bit later.) Photometric Errors Issues impacting the photometric uncertainties: • Poisson Error – Recall that the statistical uncertainty is Poisson in electrons rather than ADU.
    [Show full text]
  • REVIEW Doi:10.1038/Nature13782
    REVIEW doi:10.1038/nature13782 Highlights in the study of exoplanet atmospheres Adam S. Burrows1 Exoplanets are now being discovered in profusion. To understand their character, however, we require spectral models and data. These elements of remote sensing can yield temperatures, compositions and even weather patterns, but only if significant improvements in both the parameter retrieval process and measurements are made. Despite heroic efforts to garner constraining data on exoplanet atmospheres and dynamics, reliable interpretation has frequently lagged behind ambition. I summarize the most productive, and at times novel, methods used to probe exoplanet atmospheres; highlight some of the most interesting results obtained; and suggest various broad theoretical topics in which further work could pay significant dividends. he modern era of exoplanet research started in 1995 with the Earth-like planet requires the ability to measure transit depths 100 times discovery of the planet 51 Pegasi b1, when astronomers detected more precisely. It was not long before many hundreds of gas giants were the periodic radial-velocity Doppler wobble in its star, 51 Peg, detected both in transit and by the radial-velocity method, the former Tinduced by the planet’s nearly circular orbit. With these data, and requiring modest equipment and the latter requiring larger telescopes knowledge of the star, the orbital period (P) and semi-major axis (a) with state-of-the-art spectrometers with which to measure the small could be derived, and the planet’s mass constrained. However, the incli- stellar wobbles. Both techniques favour close-in giants, so for many nation of the planet’s orbit was unknown and, therefore, only a lower years these objects dominated the bestiary of known exoplanets.
    [Show full text]
  • The Spherical Bolometric Albedo of Planet Mercury
    The Spherical Bolometric Albedo of Planet Mercury Anthony Mallama 14012 Lancaster Lane Bowie, MD, 20715, USA [email protected] 2017 March 7 1 Abstract Published reflectance data covering several different wavelength intervals has been combined and analyzed in order to determine the spherical bolometric albedo of Mercury. The resulting value of 0.088 +/- 0.003 spans wavelengths from 0 to 4 μm which includes over 99% of the solar flux. This bolometric result is greater than the value determined between 0.43 and 1.01 μm by Domingue et al. (2011, Planet. Space Sci., 59, 1853-1872). The difference is due to higher reflectivity at wavelengths beyond 1.01 μm. The average effective blackbody temperature of Mercury corresponding to the newly determined albedo is 436.3 K. This temperature takes into account the eccentricity of the planet’s orbit (Méndez and Rivera-Valetín. 2017. ApJL, 837, L1). Key words: Mercury, albedo 2 1. Introduction Reflected sunlight is an important aspect of planetary surface studies and it can be quantified in several ways. Mayorga et al. (2016) give a comprehensive set of definitions which are briefly summarized here. The geometric albedo represents sunlight reflected straight back in the direction from which it came. This geometry is referred to as zero phase angle or opposition. The phase curve is the amount of sunlight reflected as a function of the phase angle. The phase angle is defined as the angle between the Sun and the sensor as measured at the planet. The spherical albedo is the ratio of sunlight reflected in all directions to that which is incident on the body.
    [Show full text]
  • An Introduction to Photometry and Photometric Measurements Henry
    An introduction to photometry and photometric measurements Henry Joy McCracken Institut d’Astrophysique de Paris What is photometry? • Photometry is concerned with obtaining quantitative physical measurements of astrophysical objects using electromagnetic radiation. • The challenge is to relate instrumental measurements (like electrons counted in an electronic detector) to physically meaningful quantities like flux and flux density • The ability to make quantitative measurements transformed astronomy from a purely descriptive science to one with great explanative power. To print higher-resolution math symbols, click the Hi-Res Fonts for Printing button on the jsMath control panel. Brightness and Flux Density Astronomers learn about an astronomical source by measuring the strength of its radiation as a function of direction on the sky (by mapping or imaging) and frequency (spectroscopy), plus other quantities (time, polarization) that we ignore for now. We need precise and quantitative definitions to describe the strength of radiation and how it varies with distance between the source and the observer. The concepts of brightness and flux density are deceptively simple, but they regularly trip up experienced astronomers. It is very important to understand them clearly because they are so fundamental. We start with the simplest possible case of radiation traveling from a source through empty space (so there is no absorption, scattering, or emission along the way) to an observer. In the ray-optics approximation, radiated energy flows in straight lines. This approximation is valid only for systems much larger than the wavelength of the radiation, a criterion easily met by astronomical sources. You may find it helpful to visualize electromagnetic radiation as a stream of light particles (photons), essentially bullets that travel in straight lines at the speed of light.
    [Show full text]
  • Physical Characterization of NEA Large Super-Fast Rotator (436724) 2011 UW158
    EPJ manuscript No. (will be inserted by the editor) Physical characterization of NEA Large Super-Fast Rotator (436724) 2011 UW158 A. Carbognani1, B. L. Gary2, J. Oey3, G. Baj4, and P. Bacci5 1 Astronomical Observatory of the Autonomous Region of Aosta Valley (OAVdA), Aosta - Italy 2 Hereford Arizona Observatory (Hereford, Cochise - U.S.A.) 3 Blue Mountains Observatory (Leura, Sydney - Australia) 4 Astronomical Station of Monteviasco (Monteviasco, Varese - Italy) 5 Astronomical Observatory of San Marcello Pistoiese (San Marcello Pistoiese, Pistoia - Italy) Received: date / Revised version: date Abstract. Asteroids of size larger than 0.15 km generally do not have periods smaller than 2.2 hours, a limit known as cohesionless spin-barrier. This barrier can be explained by the cohesionless rubble-pile structure model. There are few exceptions to this “rule”, called LSFRs (Large Super-Fast Rotators), as (455213) 2001 OE84, (335433) 2005 UW163 and 2011 XA3. The near-Earth asteroid (436724) 2011 UW158 was followed by an international team of optical and radar observers in 2015 during the flyby with Earth. It was discovered that this NEA is a new candidate LSFR. With the collected lightcurves from optical observations we are able to obtain the amplitude-phase relationship, sideral rotation period (PS = 0.610752 ± 0.000001 ◦ ◦ ◦ ◦ h), a unique spin axis solution with ecliptic coordinates λ = 290 ± 3 , β = 39 ± 2 and the asteroid 3D model. This model is in qualitative agreement with the results from radar observations. PACS. PACS-key discribing text of that key – PACS-key discribing text of that key 1 Introduction The near-Earth asteroid (436724) 2011 UW158 was discovered on 2011 Oct 25 by the Pan-STARRS 1 Observatory at Haleakala (Hawaii, USA).
    [Show full text]
  • The H and G Magnitude System for Asteroids
    Meetings The BAA Observers’ Workshops The H and G magnitude system for asteroids This article is based on a presentation given at the Observers’ Workshop held at the Open University in Milton Keynes on 2007 February 24. It can be viewed on the Asteroids & Remote Planets Section website at http://homepage.ntlworld.com/ roger.dymock/index.htm When you look at an asteroid through the eyepiece of a telescope or on a CCD image it is a rather unexciting point of light. However by analysing a number of images, information on the nature of the object can be gleaned. Frequent (say every minute or few min- Figure 2. The inclined orbit of (23) Thalia at opposition. utes) measurements of magnitude over periods of several hours can be used to generate a lightcurve. Analysis of such a lightcurve Absolute magnitude, H: the V-band magnitude of an asteroid if yields the period, shape and pole orientation of the object. it were 1 AU from the Earth and 1 AU from the Sun and fully Measurements of position (astrometry) can be used to calculate illuminated, i.e. at zero phase angle (actually a geometrically the orbit of the asteroid and thus its distance from the Earth and the impossible situation). H can be calculated from the equation Sun at the time of the observations. These distances must be known H = H(α) + 2.5log[(1−G)φ (α) + G φ (α)], where: in order for the absolute magnitude, H and the slope parameter, G 1 2 φ (α) = exp{−A (tan½ α)Bi} to be calculated (it is common for G to be given a nominal value of i i i = 1 or 2, A = 3.33, A = 1.87, B = 0.63 and B = 1.22 0.015).
    [Show full text]
  • PHASE CURVE of LUNAR COLOR RATIO. Yu. I. Velikodsky1, Ya. S
    42nd Lunar and Planetary Science Conference (2011) 2060.pdf PHASE CURVE OF LUNAR COLOR RATIO. Yu. I. Velikodsky1, Ya. S. Volvach2, V. V. Korokhin1, Yu. G. Shkuratov1, V. G. Kaydash1, N. V. Opanasenko1, M. M. Muminov3, and B. B. Kahharov3, 1Institute of Astro- nomy, Kharkiv National University, 35 Sumskaya Street, Kharkiv, 61022, Ukraine, [email protected], 2Phy- sical Faculty, Kharkiv National University, 4 Svobody Square, Kharkiv, 61077, Ukraine, 3Andijan-Namangan Sci- entific Center of Uzbekistan Academy of Sciences, 38 Cho'lpon Street, Andijan city, 170020, Uzbekistan. Introduction: The dependence of a color ratio of and "B": 472 nm) in a wide range of phase angles (1.6– the lunar surface on phase angle α is poorly studied. 168°) and zenith distances. The ratio, which is defined as C(λ1/λ2)=A(λ1)/A(λ2), At present time, we have computed radiance factor where A is the radiance factor (apparent albedo), λ is maps in spectral bands "R" and "B" at α in the range the wavelength (λ1>λ2), is believed to increase mono- 3–73° with a resolution of 2 km near the lunar disk tonically in the visible spectral range with increasing α center. Using the radiance factor distributions, we have in the range 0–90° by 10–15% [1,2]. From the ground obtained 22 maps of lunar color ratio C(603/472 nm). based colorimetry [3] it has been found that at α < 40– An example of such a map at α=16° is shown in Fig. 2. 50° the color ratio C(603/472 nm) for lunar highlands Phase curve of color ratio: Using the maps of co- grows with α faster than that of the mare regions.
    [Show full text]